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3 pages, 171 KiB

Open AccessEditorial

Special Issue on “CFD Based Researches and Applications for Fluid Machinery and Fluid Device”

by Jin-Hyuk Kim, Sung-Min Kim, Minsuk Choi, Lei Tan, Bin Huang and Ji Pei

Processes 2021, 9(7), 1137; https://doi.org/10.3390/pr9071137 - 30 Jun 2021

Cited by 1 | Viewed by 1743

Abstract

The demand for computational fluid dynamics (CFD)-based numerical techniques is increasing rapidly with the development of the computing power system [...] Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

Research

Jump to: Editorial

16 pages, 5652 KiB

Open AccessArticle

Effects of Micro-Tab on the Lift Enhancement of Airfoil S-809 with Trailing-Edge Flap

by Jianjun Ye, Shehab Salem, Juan Wang, Yiwen Wang, Zonggang Du and Wei Wang

Processes 2021, 9(3), 547; https://doi.org/10.3390/pr9030547 - 19 Mar 2021

Cited by 2 | Viewed by 2571

Abstract

Recently, the Trailing-Edge Flap with Micro-Tab (TEF with Micro-Tab) has been exploited to enhance the performance of wind turbine blades. Moreover, it can also be used to generate more lift and delay the onset of stall. This study focused mostly on the use [...] Read more.

Recently, the Trailing-Edge Flap with Micro-Tab (TEF with Micro-Tab) has been exploited to enhance the performance of wind turbine blades. Moreover, it can also be used to generate more lift and delay the onset of stall. This study focused mostly on the use of TEF with Micro-Tab in wind turbine blades using NREL’s S-809 as a model airfoil. In particular, the benefits generated by TEF with Micro-Tab may be of great interest in the design of wind turbine blades. In this paper, an attempt was made to evaluate the influence of TEF with Micro-Tab on the performance of NREL’s S-809 airfoils. Firstly, a computational fluid dynamics (CFD) model for the airfoil NREL’s S-809 was established, and validated by comparison with previous studies and wind tunnel experimental data. Secondly, the effects of the flap position (H) and deflection angle (α_F) on the flow behaviors were investigated. As a result, the effect of TEF on air-flow behavior was demonstrated by augmenting the pressure coefficient at the lower surface of the airfoil at flap position 80% chord length (C) and α_F = 7.5°. Thirdly, the influence of TEF with Micro-Tab on the flow behaviors of the airfoil NREL’s S-809 was studied and discussed. Different Micro-Tab positions and constant TEF were examined. Finally, the effects of TEF with Micro-Tab on the aerodynamic characteristics of the S-809 with TEF were compared. The results showed that an increase in the maximum lift coefficient by 25% and a delay in the air-flow stall were accomplished due to opposite sign vortices, which was better than the standard airfoil and S-809 with TEF. Therefore, it was deduced that the benefits of TEF with Micro-Tab were apparent, especially at the lower surface of the airfoil. This particularly suggests that the developed model could be used as a new trend to modify the designs of wind turbine blades. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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18 pages, 6847 KiB

Open AccessArticle

Effect of an Inducer-Type Guide Vane on Hydraulic Losses at the Inter-Stage Flow Passage of a Multistage Centrifugal Pump

by Mohamed Murshid Shamsuddeen, Sang-Bum Ma, Sung Kim, Ji-Hoon Yoon, Kwang-Hee Lee, Changjun Jung and Jin-Hyuk Kim

Processes 2021, 9(3), 526; https://doi.org/10.3390/pr9030526 - 15 Mar 2021

Cited by 7 | Viewed by 5358

Abstract

A multistage centrifugal pump was developed for high head and high flow rate applications. A double-suction impeller and a twin-volute were installed at the first stage followed by an impeller, diffuser and return vanes for the next four stages. An initial design feasibility [...] Read more.

A multistage centrifugal pump was developed for high head and high flow rate applications. A double-suction impeller and a twin-volute were installed at the first stage followed by an impeller, diffuser and return vanes for the next four stages. An initial design feasibility study was conducted using three-dimensional computational fluid dynamics tools to study the performance and the hydraulic losses associated with the design. Substantial losses in head and efficiency were observed at the interface between the first stage volute and the second stage impeller. An inducer-type guide vane (ITGV) was installed at this location to mitigate the losses by reducing the circumferential velocity of the fluid exiting the volute. The ITGV regulated the pre-swirl of the fluid entering the second stage impeller. The pump with and without ITGV is compared at the design flow rate. The pump with ITGV increased the stage head by 63.28% and stage efficiency by 47.17% at the second stage. As a result, the overall performance of the pump increased by 5.78% and 3.94% in head and efficiency, respectively, at the design point. The ITGV has a significant impact on decreasing losses at both design and off-design conditions. An in-depth flow dynamic analysis at the inducer-impeller interface is also presented. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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18 pages, 9075 KiB

Open AccessArticle

Testing the Accuracy of the Cell-Set Model Applied on Vane-Type Sub-Boundary Layer Vortex Generators

by Koldo Portal-Porras, Unai Fernandez-Gamiz, Iñigo Aramendia, Daniel Teso-Fz-Betoño and Ekaitz Zulueta

Processes 2021, 9(3), 503; https://doi.org/10.3390/pr9030503 - 11 Mar 2021

Cited by 9 | Viewed by 2067

Abstract

Vortex Generators (VGs) are applied before the expected region of separation of the boundary layer in order to delay or remove the flow separation. Although their height is usually similar to that of the boundary layer, in some applications, lower VGs are used, [...] Read more.

Vortex Generators (VGs) are applied before the expected region of separation of the boundary layer in order to delay or remove the flow separation. Although their height is usually similar to that of the boundary layer, in some applications, lower VGs are used, Sub-Boundary Layer Vortex Generators (SBVGs), since this reduces the drag coefficient. Numerical simulations of sub-boundary layer vane-type vortex generators on a flat plate in a negligible pressure gradient flow were conducted using the fully resolved mesh model and the cell-set model, with the aim on assessing the accuracy of the cell-set model with Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence modelling techniques. The implementation of the cell-set model has supposed savings of the 40% in terms of computational time. The vortexes generated on the wake behind the VG; vortical structure of the primary vortex; and its path, size, strength, and produced wall shear stress have been studied. The results show good agreements between meshing models in the higher VGs, but slight discrepancies on the lower ones. These disparities are more pronounced with LES. Further study of the cell-set model is proposed, since its implementation entails great computational time and resources savings. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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19 pages, 8082 KiB

Open AccessArticle

Investigation on Dynamic Stresses of Pump-Turbine Runner during Start Up in Turbine Mode

by Funan Chen, Huili Bi, Soo-Hwang Ahn, Zhongyu Mao, Yongyao Luo and Zhengwei Wang

Processes 2021, 9(3), 499; https://doi.org/10.3390/pr9030499 - 10 Mar 2021

Cited by 25 | Viewed by 2247

Abstract

The startup process occurs frequently for pumped storage units. During this process, the rotating rate that changes rapidly and unsteady flow in runner cause the complex dynamic response of runner, sometimes even resonance. The sharp rise of stress and the large-amplitude dynamic stresses [...] Read more.

The startup process occurs frequently for pumped storage units. During this process, the rotating rate that changes rapidly and unsteady flow in runner cause the complex dynamic response of runner, sometimes even resonance. The sharp rise of stress and the large-amplitude dynamic stresses of runner will greatly shorten the fatigue life. Thus, the study of start-up process in turbine mode is critical to the safety operation. This paper introduced a method of coupling one dimensional (1D) pipeline calculation and three-dimensional computational dynamics (3D CFD) simulation to analyze transient unsteady flow in units and to obtain more accurate and reliable dynamic stresses results during start up process. According to the results, stress of the ring near fixed support increased quickly as rotating rate rose and became larger than at fillets of leading edge and band in the later stages of start-up. In addition, it was found that dynamic response can be caused by rotor stator interaction (RSI), but also could even be generated by the severe pressure fluctuation in clearance, which can also be a leading factor of dynamic stresses. This study will facilitate further estimation of dynamic stresses in complex flow and changing rotating rate cases, as well as fatigue analysis of runner during transient operation. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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19 pages, 8431 KiB

Open AccessArticle

Optimization of a Wavy Microchannel Heat Sink with Grooves

by Min-Cheol Park, Sang-Bum Ma and Kwang-Yong Kim

Processes 2021, 9(2), 373; https://doi.org/10.3390/pr9020373 - 18 Feb 2021

Cited by 14 | Viewed by 3300

Abstract

In this study, a wavy microchannel heat sink with grooves using water as the working fluid is proposed for application to cooling microprocessors. The geometry of the heat sink was optimized to improve heat transfer and pressure loss simultaneously. To achieve optimization goals, [...] Read more.

In this study, a wavy microchannel heat sink with grooves using water as the working fluid is proposed for application to cooling microprocessors. The geometry of the heat sink was optimized to improve heat transfer and pressure loss simultaneously. To achieve optimization goals, the average friction factor and thermal resistance were used as the objective functions. Three dimensionless parameters were selected as design variables: the distance between staggered grooves, groove width, and groove depth. A modified Latin hypercube sampling (LHS) method that combines the advantages of conventional LHS and a three-level full factorial method is also proposed. Response surface approximation was used to construct surrogate models, and Pareto-optimal solutions were obtained with a multi-objective genetic algorithm. The modified LHS was proven to have better performance than the conventional LHS and full factorial methods in the present optimization problem. A representative optimal design showed that both the thermal resistance and friction factor improved by 1.55% and 3.00%, compared to a reference design, respectively. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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15 pages, 4944 KiB

Open AccessArticle

Optimization Control on the Mixed Free-Surface-Pressurized Flow in a Hydropower Station

by Xinlong Wang, Honggang Fan and Bing Liu

Processes 2021, 9(2), 320; https://doi.org/10.3390/pr9020320 - 9 Feb 2021

Cited by 3 | Viewed by 2065

Abstract

The mixed free-surface-pressurized flow in the tailrace tunnel of a hydropower station has a great impact on the pressure, velocity, and operation stability of the power station. In the present work, a characteristic implicit method based on the upwind differencing and implicit finite [...] Read more.

The mixed free-surface-pressurized flow in the tailrace tunnel of a hydropower station has a great impact on the pressure, velocity, and operation stability of the power station. In the present work, a characteristic implicit method based on the upwind differencing and implicit finite difference scheme is used to solve the mixed free-surface-pressurized flow. The results of the characteristic implicit method agree well with the experimental results, which validates the accuracy of the method. Four factors that influence the amplitude of pressure fluctuation are analyzed and optimized, and the results show that the relative roughness can influence the maximum pressure in the tailrace tunnel. Additionally, the maximum pressure decreases with the increase of the tunnel’s relative roughness. When the surface relative roughness increases from 0.010 to 0.018, the maximum pressure can decrease by 4.33%. The maximum pressure in the tailrace tunnel can be effectively restrained by setting vent holes in the flat-topped tunnel section (tunnel (4)) and a vent hole at 81.25%L (L is the length of tunnel (4)), which can reduce the maximum pressure by 56.72%. Increasing the vent hole number can also reduce the maximum pressure of the mixed free-surface-pressurized flow in the tailrace tunnel. An optimal set of two ventilation holes 10 m in diameter at 93.75%L and 56.25%L is proposed, which can reduce the maximum pressure by 15.30% in comparison with the single vent case. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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24 pages, 13919 KiB

Open AccessArticle

Development of a Hydropower Turbine Using Seawater from a Fish Farm

by Md Rakibuzzaman, Sang-Ho Suh, Hyoung-Ho Kim, Youngtae Ryu and Kyung Yup Kim

Processes 2021, 9(2), 266; https://doi.org/10.3390/pr9020266 - 30 Jan 2021

Cited by 8 | Viewed by 4921

Abstract

Discharge water from fish farms is a clean, renewable, and abundant energy source that has been used to obtain renewable energy via small hydropower plants. Small hydropower plants may be installed at offshore fish farms where suitable water is obtained throughout the year. [...] Read more.

Discharge water from fish farms is a clean, renewable, and abundant energy source that has been used to obtain renewable energy via small hydropower plants. Small hydropower plants may be installed at offshore fish farms where suitable water is obtained throughout the year. It is necessary to meet the challenges of developing small hydropower systems, including sustainability and turbine efficiency. The main objective of this study was to investigate the possibility of constructing a small hydropower plant and develop 100 kW class propeller-type turbines in a fish farm with a permanent magnet synchronous generator (PMSG). The turbine was optimized using a computer simulation, and an experiment was conducted to obtain performance data. Simulation results were then validated with experimental results. Results revealed that streamlining the designed shape of the guide vane reduced the flow separation and improved the efficiency of the turbine. Optimizing the shape of the runner vane decreased the flow rate, reducing the water power and increasing the efficiency by about 5.57%. Also, results revealed that tubular or cross-flow turbines could be suitable for use in fish farm power plants, and the generator used should be waterproofed to avoid exposure to seawater. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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16 pages, 6773 KiB

Open AccessArticle

Matching Optimization of a Mixed Flow Pump Impeller and Diffuser Based on the Inverse Design Method

by Mengcheng Wang, Yanjun Li, Jianping Yuan and Fareed Konadu Osman

Processes 2021, 9(2), 260; https://doi.org/10.3390/pr9020260 - 29 Jan 2021

Cited by 16 | Viewed by 3053

Abstract

When considering the interaction between the impeller and diffuser, it is necessary to provide logical and systematic guidance for their matching optimization. In this study, the goal was to develop a comprehensive matching optimization strategy to optimize the impeller and diffuser of a [...] Read more.

When considering the interaction between the impeller and diffuser, it is necessary to provide logical and systematic guidance for their matching optimization. In this study, the goal was to develop a comprehensive matching optimization strategy to optimize the impeller and diffuser of a mixed flow pump. Some useful tools and methods, such as the inverse design method, computational fluid dynamics (CFD), design of experiment, surrogate model, and optimization algorithm, were used. The matching optimization process was divided into two steps. In the first step, only the impeller was optimized. Thereafter, CFD analysis was performed on the optimized impeller to get the circulation and flow field distribution at the outlet of the impeller. In the second step of optimization, the flow field and circulation distribution at the inlet of the diffuser were set to be the same as the optimized impeller outlet. The results show that the matching optimization strategy proposed in this study is effective and can overcome the shortcomings of single-component optimization, thereby further improving the overall optimization effect. Compared with the baseline model, the pump efficiency of the optimized model at 1.2Q_des, 1.0Q_des, and 0.8Q_des is increased by 6.47%, 3.68%, and 0.82%, respectively. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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12 pages, 3367 KiB

Open AccessArticle

The Influence of Hydrodynamic Changes in a System with a Pitched Blade Turbine on Mixing Power

by Jacek Stelmach, Czesław Kuncewicz, Szymon Szufa, Tomas Jirout and Frantisek Rieger

Processes 2021, 9(1), 68; https://doi.org/10.3390/pr9010068 - 30 Dec 2020

Cited by 19 | Viewed by 3066

Abstract

This paper presents an analysis of hydrodynamics in a tank with a 45° and 60° pitched blade turbine impeller operating while emptying the mixer and with an axial agitator working during axial pumping-down of water at different water levels above the impeller. Measurements [...] Read more.

This paper presents an analysis of hydrodynamics in a tank with a 45° and 60° pitched blade turbine impeller operating while emptying the mixer and with an axial agitator working during axial pumping-down of water at different water levels above the impeller. Measurements made with the PIV method confirmed the change in direction of pumping liquid after the level dropped below the critical value, with an almost unchanged liquid stream flowing through the mixer. It was found that an increase in the value of the tangential velocity in the area of the impeller took place and the quantity of this increase depended on the angle of the blade pitch and the rotational frequency of the impeller. Change in this velocity component increased the mixing power. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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12 pages, 3940 KiB

Open AccessArticle

New Design of the Reversible Jet Fan

by Miroslav H. Benišek, Đorđe S. Čantrak, Dejan B. Ilić and Novica Z. Janković

Processes 2020, 8(12), 1671; https://doi.org/10.3390/pr8121671 - 17 Dec 2020

Cited by 4 | Viewed by 4499

Abstract

This paper presents two designs of the axial reversible jet fan, with the special focus on the impeller. The intention was to develop a reversible axial jet fan which operates in the same way in both rotating directions while generating thrust as high [...] Read more.

This paper presents two designs of the axial reversible jet fan, with the special focus on the impeller. The intention was to develop a reversible axial jet fan which operates in the same way in both rotating directions while generating thrust as high as possible. The jet fan model with the outer diameter 499.2 ± 0.1 mm and ten adjustable blades is the same, while it is in-built in two different casings. The first construction is a cylindrical casing, while the second one is profiled as a nozzle. Thrust, volume flow rate, consumed power and ambient conditions were measured after the international standard ISO 13350. Results for both constructions are presented for three impeller blade angles: 28°, 31° and 35°, and rotation speed in the interval n = 400 to 2600 rpm. The smallest differences in thrust, depending on the fan rotation direction, as well as the highest thrust are achieved for the first design with the cylindrical casing and blade angle at the outer diameter of 35°. Therefore, it was shown that fan casing significantly influences jet fan characteristics. In addition, the maximum thrust value and its independence of the flow direction is experimentally obtained for the angle of 39° in the cylindrical casing. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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16 pages, 6534 KiB

Open AccessArticle

Numerical and Experimental Study on Waviness Mechanical Seal of Reactor Coolant Pump

by Xiaodong Feng, Wentao Su, Yu Ma, Lei Wang and Heping Tan

Processes 2020, 8(12), 1611; https://doi.org/10.3390/pr8121611 - 7 Dec 2020

Cited by 7 | Viewed by 2957

Abstract

Based on the fluid hydrodynamic lubrication theory, a mathematical model of liquid film lubrication was established for the waviness hydrodynamic mechanical seal of a reactor coolant pump. The influences of the waviness amplitude and pressure on the sealing performance were investigated by the [...] Read more.

Based on the fluid hydrodynamic lubrication theory, a mathematical model of liquid film lubrication was established for the waviness hydrodynamic mechanical seal of a reactor coolant pump. The influences of the waviness amplitude and pressure on the sealing performance were investigated by the numerical simulation. The numerical results showed that the leakage rate increases linearly as the pressure and waviness amplitude increase under the force balance condition. The minimum liquid film thickness decreases first and then increase as the pressure increases. Stationary slide rings with three different waviness amplitudes were processed using the pre-deformation method and tested at different pressure and temperature. The experiments showed that all the three kinds of seal have good stability under different pressure conditions. The experimental results showed that the leakage rate is influenced by the pressure, waviness amplitude, and temperature, and the leakage rate increases as the pressure increases. The comparison between experimental and numerical results showed that both the temperature and pressure affect the seal performance, and tends to a smaller leakage rate, which is quite different from the numerical values. Therefore, the multi-physics coupling effect should be considered in the numerical analysis of seal performance, and this will be studied in the further works. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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19 pages, 13844 KiB

Open AccessArticle

Numerical Investigation of an Open-Design Vortex Pump with Different Blade Wrap Angles of Impeller

by Xiongfa Gao, Ting Zhao, Weidong Shi, Desheng Zhang, Ya Shi, Ling Zhou and Hao Chang

Processes 2020, 8(12), 1601; https://doi.org/10.3390/pr8121601 - 4 Dec 2020

Cited by 7 | Viewed by 3167

Abstract

The blade wrap angle of impeller is an important structural parameter in the hydraulic design of open-design vortex pump. In this paper, taking a vortex pump with a cylindrical blade structure as the research object, two kinds of different blade wrap angle of [...] Read more.

The blade wrap angle of impeller is an important structural parameter in the hydraulic design of open-design vortex pump. In this paper, taking a vortex pump with a cylindrical blade structure as the research object, two kinds of different blade wrap angle of vortex pump impellers are designed. The experiment and numerical simulation research is carried out, and the results of external characteristics and internal flow field are obtained under different flow rate. The results show that when ensuring that other main structural parameters remain unchanged, the efficiency and head of open-design vortex pump increase with the blade wrap angle decreases. In the case of blade wrap angle increasing, the length of rotating reflux back from lateral cavity to inlet is longer. For the same type of vortex pump, the length of rotating reflux to inlet decreases with the increase of flow rate. At the inlet area of impeller front face, there is an area where liquid flows back to the lateral cavity. The volute section shows that after passing through the impeller and lateral cavity, the liquid is discharged to the pump outlet with strong spiral strength. It is found that the blade wrap angle decreases and the shaft power increases, while the pump efficiency increases. The impeller blade wrap angle of vortex pump can be considered to select a smaller value. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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17 pages, 8415 KiB

Open AccessArticle

The Effect of Root Clearance on Mechanical Energy Dissipation for Axial Flow Pump Device Based on Entropy Production

by Yanjun Li, Yunhao Zheng, Fan Meng and Majeed Koranteng Osman

Processes 2020, 8(11), 1506; https://doi.org/10.3390/pr8111506 - 20 Nov 2020

Cited by 18 | Viewed by 2660

Abstract

The axial flow pump is a low head, high discharge pump usually applicable in drainage and irrigation facilities. A certain gap should be reserved between the impeller blade root and the impeller hub to ensure the blade adjustability to broaden the high-efficiency area. [...] Read more.

The axial flow pump is a low head, high discharge pump usually applicable in drainage and irrigation facilities. A certain gap should be reserved between the impeller blade root and the impeller hub to ensure the blade adjustability to broaden the high-efficiency area. The pressure difference between its blade surface induces leakage flow in the root clearance region, which decreases hydraulic performance and operational stability. Therefore, this study was carried out to investigate the effect of root clearance on mechanical energy dissipation using numerical simulation and entropy production methods. The numerical model was validated with an external characteristics test, and unsteady flow simulations were conducted on the axial flow pump under four different root clearance radii. The maximum reductions of 15.5% and 6.8% for head and hydraulic efficiency are obtained for the largest root clearance of 8 mm, respectively. The dissipation based on entropy theory consists of indirect dissipation and neglectable direct dissipation. The leakage flow in the root clearance led to the distortion of the impeller’s flow pattern, and the indirect dissipation rate and overall dissipation of the impeller increased with increasing root clearance radius. The inflow pattern in the diffuser was also distorted by leakage flow. The diffuser’s overall dissipation, indirect dissipation rate on the blade surface, and indirect dissipation rate near inlet increased with increasing root clearance radius. The research could serve as a theoretical reference for the axial flow pump’s root clearance design for performance improvement and operational stability. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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17 pages, 7206 KiB

Open AccessFeature PaperArticle

Effect of Clearance and Cavity Geometries on Leakage Performance of a Stepped Labyrinth Seal

by Min Seok Hur, Soo In Lee, Seong Won Moon, Tong Seop Kim, Jae Su Kwak, Dong Hyun Kim and Il Young Jung

Processes 2020, 8(11), 1496; https://doi.org/10.3390/pr8111496 - 19 Nov 2020

Cited by 15 | Viewed by 4996

Abstract

This study evaluated the leakage characteristics of a stepped labyrinth seal. Experiments and computational fluid dynamics (CFD) analysis were conducted for a wide range of pressure ratios and clearance sizes, and the effect of the clearance on the leakage characteristics was analyzed by [...] Read more.

This study evaluated the leakage characteristics of a stepped labyrinth seal. Experiments and computational fluid dynamics (CFD) analysis were conducted for a wide range of pressure ratios and clearance sizes, and the effect of the clearance on the leakage characteristics was analyzed by determining the performance of the seal using a dimensionless parameter. It was observed from the analysis that the performance parameter of the seal decreases as the clearance size increases, but it tends to increase when the clearance size exceeds a certain value. In other words, it was revealed that there exists a specific clearance size (S_min) which minimizes the performance parameter of the seal. To identify the cause of this tendency change, a flow analysis was conducted using CFD. It was confirmed that the leakage characteristics of the stepped seal are affected by the size of the cavity, which is the space between the teeth. Therefore, a parametric study was conducted on the design parameters related to the cavity size (tooth height and pitch). The results show that the performance parameter decreases as the tooth height and pitch decreases. Moreover, S_min increases as the tooth height increases and the pitch decreases. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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20 pages, 10684 KiB

Open AccessArticle

Influence of Tip Clearance on Flow Characteristics of Axial Compressor

by Moru Song, Hong Xie, Bo Yang and Shuyi Zhang

Processes 2020, 8(11), 1445; https://doi.org/10.3390/pr8111445 - 11 Nov 2020

Cited by 6 | Viewed by 3005

Abstract

This paper studies the influence of tip clearance on the flow characteristics related to the performance. Based on full-passage numerical simulation with experimental validation, several clearance models are established and the performance curves are obtained. It is found that there exists an optimum [...] Read more.

This paper studies the influence of tip clearance on the flow characteristics related to the performance. Based on full-passage numerical simulation with experimental validation, several clearance models are established and the performance curves are obtained. It is found that there exists an optimum clearance for the stable working range. By analyzing the flow field in tip region, the role of the tip leakage flow is illustrated. In the zero-clearance model, the separation and blockage along the suction side is the main reason for rotating stall. As the tip clearance is increased to the optimum value, the separation is suppressed by the tip leakage flow. However, with the continuing increasing of the tip clearance, the scale and strength of the tip clearance vortex is increased correspondingly. When the tip clearance is larger than the optimum value, the tip clearance vortex gradually dominates the flow field in the tip region, which can increase the unsteadiness in the tip region and trigger forward spillage in stall onset. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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17 pages, 10334 KiB

Open AccessFeature PaperArticle

Large Eddy Simulation of Film Cooling with Triple Holes: Injectant Behavior and Adiabatic Film-Cooling Effectiveness

by Seung Il Baek and Joon Ahn

Processes 2020, 8(11), 1443; https://doi.org/10.3390/pr8111443 - 11 Nov 2020

Cited by 6 | Viewed by 2439

Abstract

This study investigated the effect of adding two sister holes placed downstream the main hole on film cooling by employing large eddy simulation. Here, film-cooling flow fields from a triple-hole system inclined by 35° to a flat plate at blowing ratios of M [...] Read more.

This study investigated the effect of adding two sister holes placed downstream the main hole on film cooling by employing large eddy simulation. Here, film-cooling flow fields from a triple-hole system inclined by 35° to a flat plate at blowing ratios of M = 0.5 and unity were simulated. Each sister hole supplies a cooling fluid at a flow rate that is a quarter of that for the main hole. The simulations were conducted using the Smagorinsky–Lilly model as the subgrid-scale model, and the results were compared with those for a single-hole system for the same amount of total cooling air and same cross-sectional area of the holes. Relative to the single-hole system, the spanwise-averaged film-cooling effectiveness in the triple-hole configuration at M = 1.0 increased by as much as 345%. The subsequent proper orthogonal decomposition analysis showed that the kinetic energy of a counter-rotating vortex pair in the triple-hole system dropped by 30–40% relative to that of the single-hole system. This indicates that the additional sister holes promoted the suppression of the mixing of the coolant jet with the mainstream flow, thus keeping the temperature of the latter low. Cross-sectional views of the root-mean-square temperature contours were also analyzed; with the results confirming that the effect of the sister holes on the jet trajectory greatly contributes in promoting film-cooling effectiveness as compared to the effect of the reduced mixing. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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28 pages, 14785 KiB

Open AccessArticle

Experimental and Comparative RANS/URANS Investigations on the Effect of Radius of Volute Tongue on the Aerodynamics and Aeroacoustics of a Sirocco Fan

by Xiaocheng Rui, Limin Lin, Junkui Wang, Xinxue Ye, Haijiang He, Wei Zhang and Zuchao Zhu

Processes 2020, 8(11), 1442; https://doi.org/10.3390/pr8111442 - 11 Nov 2020

Cited by 7 | Viewed by 2647

Abstract

The geometry of volute tongue is crucial in the design of Sirocco fans. The size of the volute tongue determines its relative position and distance from the impeller which affects the local flow characteristics and thus the aerodynamic and aeroacoustic performances of the [...] Read more.

The geometry of volute tongue is crucial in the design of Sirocco fans. The size of the volute tongue determines its relative position and distance from the impeller which affects the local flow characteristics and thus the aerodynamic and aeroacoustic performances of the fan. In this work, we performed experimental and numerical investigations on the effect of volute tongue radius on the aerodynamic and aeroacoustic characteristics of a Sirocco fan. The internal flow characteristics are analyzed and discussed in terms of the spatial distribution and temporal variation of pressure and streamlines, the pulsating behaviors of pressure both in the impeller and on the volute surface with emphasis in the volute tongue region, the variation of passage flow with the rotation of impeller and the aeroacoustic features of the fan. We conducted numerical simulations using both steady Reynolds-Averaged Navier-Stokes (RANS) and unsteady Reynolds-Averaged Navier-Stokes (URANS) approaches with realizable k-ε turbulence model with rotation effect correction and the results are compared against the experimental data to assess the prediction capability and accuracy in qualitative and quantitative manners. Experimental and numerical results show that as the volute tongue radius increases, the static pressure rises as well as the far-field noise of the fan and pronounced fluctuation of flow is observed within the whole impeller and volute; the reversed flow in the passage of the impeller is reduced and the high-pressure region is found to be moving towards the outlet of the volute. The decreasing radius also enlarges the size of the adverse pressure gradient (APG) region on the volute tongue which contributes to the formation of recirculating flow. The comparative RANS and URANS simulations reveal that both approaches produce generally consistent results regarding the time-averaged flow although the URANS data are much closer to those of the experimental ones. However, the fluctuating flow which is not capable to be modeled by RANS still dominates for the present configuration and thus URANS is necessary for the accurate prediction of the flow details. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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14 pages, 7013 KiB

Open AccessArticle

The Influence of the Blade Outlet Angle on the Flow Field and Pressure Pulsation in a Centrifugal Fan

by Hongchang Ding, Tao Chang and Fanyun Lin

Processes 2020, 8(11), 1422; https://doi.org/10.3390/pr8111422 - 8 Nov 2020

Cited by 21 | Viewed by 6111

Abstract

This paper takes centrifugal fan as the research object and establishes five impeller models with different blade outlet angles. By means of computational fluid dynamics (CFD), the external characteristics of the centrifugal fan and the internal characteristics, including the velocity, pressure, and turbulent [...] Read more.

This paper takes centrifugal fan as the research object and establishes five impeller models with different blade outlet angles. By means of computational fluid dynamics (CFD), the external characteristics of the centrifugal fan and the internal characteristics, including the velocity, pressure, and turbulent energy distribution, at the middle span plane of the impeller or fan were obtained and compared. In addition, the pressure fluctuations surrounding the impeller outlet were also analyzed. The results showed that the change of the blade outlet angle of the centrifugal fan had a great influence on the performance; the total pressure and efficiency of the fan were the highest when the outlet angle of the blade was increased to 29.5° under the design flow rate; and the influence of the outlet angle on the fan performance was different in off-design conditions. On the other hand, at different flow rates, the change of the internal flow field with the increase of the outlet angle was different. For the pressure fluctuation of the fan, by increasing the blade outlet angle properly under high flow conditions, the fluctuation amplitude of the fan at the blade frequency and its frequency multiplication could be reduced, which is conducive to decreasing the impeller noise. The research results have good guiding significance regarding the design of the pneumatic performance and noise reduction performance of centrifugal fans. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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22 pages, 9008 KiB

Open AccessFeature PaperArticle

A CFD-Based Shape Design Optimization Process of Fixed Flow Passages in a Francis Hydro Turbine

by Ujjwal Shrestha and Young-Do Choi

Processes 2020, 8(11), 1392; https://doi.org/10.3390/pr8111392 - 31 Oct 2020

Cited by 14 | Viewed by 4226

Abstract

In recent times, optimization began to be popular in the turbomachinery field. The development of computational fluid dynamics (CFD) analysis and optimization technology provides the opportunity to maximize the performance of hydro turbines. The optimization techniques are focused mainly on the rotating components [...] Read more.

In recent times, optimization began to be popular in the turbomachinery field. The development of computational fluid dynamics (CFD) analysis and optimization technology provides the opportunity to maximize the performance of hydro turbines. The optimization techniques are focused mainly on the rotating components (runner and guide vane) of the hydro turbines. Meanwhile, fixed flow passages (stay vane, casing, and draft tube) are essential parts for the proper flow uniformity in the hydro turbines. The suppression of flow instabilities in the fixed flow passages is an inevitable process to ensure the power plant safety by the reduction of vortex-induced vibration and pressure pulsation in the hydro turbines. In this study, a CFD-based shape design optimization process is proposed with response surface methodology (RSM) to improve the flow uniformity in the fixed flow passages of a Francis hydro turbine model. The internal flow behaviors were compared between the initial and optimal shapes of the stay vane, casing, and the draft tube with J-Groove. The optimal shape design process for the fixed flow passages proved its remarkable effects on the improvement of flow uniformity in the Francis hydro turbine. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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12 pages, 8014 KiB

Open AccessArticle

Aerodynamic Performance of an Octorotor SUAV with Different Rotor Spacing in Hover

by Yao Lei, Yuhui Huang and Hengda Wang

Processes 2020, 8(11), 1364; https://doi.org/10.3390/pr8111364 - 28 Oct 2020

Cited by 8 | Viewed by 2495

Abstract

To study the aerodynamic performance of hovering octorotor small unmanned aerial vehicles (SUAV) with different rotor spacing, the computational fluid dynamics (CFD) method is applied to analyze the flow field of an octorotor SUAV in detail. In addition, an experimental platform is built [...] Read more.

To study the aerodynamic performance of hovering octorotor small unmanned aerial vehicles (SUAV) with different rotor spacing, the computational fluid dynamics (CFD) method is applied to analyze the flow field of an octorotor SUAV in detail. In addition, an experimental platform is built to measure the thrust and power of the rotors with rotor spacing ratios L/D of 1.0, 1.2, 1.4, 1.6, and 1.8, sequentially. According to the theory of momentum, rotor aerodynamic performance is obtained with qualitative analysis. Further analysis with numerical simulation is presented with the flow field of the octorotor SUAV, the vorticity distribution, velocity distribution, pressure distribution, and streamline. The results show that the aerodynamic performance varies with the rotor spacing. Specifically, the aerodynamic performance is poor at L/D = 1.0, which is accompanied with strong interaction of wake and tip vortexes and interaction with each other. However, the aerodynamic efficiency is much improved with a larger rotor spacing, especially achieving the highest at L/D = 1.8, which is considered to be the best rotor spacing ratio for this kind of octorotor SUAV. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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14 pages, 4251 KiB

Open AccessArticle

Effect of Rotor Spacing and Duct Diffusion Angle on the Aerodynamic Performances of a Counter-Rotating Ducted Fan in Hover Mode

by Woo-Yul Kim, Santhosh Senguttuvan and Sung-Min Kim

Processes 2020, 8(11), 1338; https://doi.org/10.3390/pr8111338 - 23 Oct 2020

Cited by 8 | Viewed by 3906

Abstract

The aerodynamic performance of a counter-rotating ducted fan in hover mode is numerically analyzed for different rotor spacings and duct diffusion angles. The design of the counter-rotating fan is inspired by a custom-designed single rotor ducted fan used in a previous study. The [...] Read more.

The aerodynamic performance of a counter-rotating ducted fan in hover mode is numerically analyzed for different rotor spacings and duct diffusion angles. The design of the counter-rotating fan is inspired by a custom-designed single rotor ducted fan used in a previous study. The numerical model to predict the aerodynamic performance of the counter-rotating ducted fan is developed by adopting the frozen rotor approach for steady-state incompressible flow conditions. The relative angle between the front and the rear rotor is examined due to the usage of the frozen rotor model. The results show that the variation of thrust for the different relative angles is extremely low. The aerodynamic performances are evaluated by comparing the thrust, thrust coefficient, power coefficient, and figure of merit (FOM). The thrust, thrust coefficient, and FOM slightly increase with increasing rotor spacing up to 200 mm, regardless of the duct diffusion angle, and reduce on further increase in the rotor spacing. The duct diffusion angle of 0° generates about 9% higher thrust and increases the FOM by 6.7%, compared with the 6° duct diffusion angle. The duct diffusion angle is highly effective in improving the thrust and FOM of the counter-rotating ducted fan, rather than the rotor spacing. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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15 pages, 7214 KiB

Open AccessArticle

Thermal Performance of T-shaped Obstacles in a Solar Air Heater

by Seung-Yong Ahn and Kwang-Yong Kim

Processes 2020, 8(10), 1305; https://doi.org/10.3390/pr8101305 - 17 Oct 2020

Cited by 6 | Viewed by 2985

Abstract

This paper proposes T-shaped ribs as obstacles attached to the heat absorber plate in a rectangular solar air heater to promote heat transfer. The thermal and aerodynamic performance of the solar heater was numerically evaluated using three-dimensional Reynolds-averaged Navier–Stokes equations with the shear [...] Read more.

This paper proposes T-shaped ribs as obstacles attached to the heat absorber plate in a rectangular solar air heater to promote heat transfer. The thermal and aerodynamic performance of the solar heater was numerically evaluated using three-dimensional Reynolds-averaged Navier–Stokes equations with the shear stress transport turbulence model. A parameter study was performed using the ratios of rib height to channel height, rib width to channel width, and rib width to rib height. The area-averaged Nusselt number and friction factor were selected as the performance parameters of the solar air heater to evaluate the heat transfer and friction loss, respectively. In addition, the performance factor was defined as the ratio of the area-averaged Nusselt number to the friction factor. The maximum area-averaged Nusselt number was found at h/e = 0.83 for a fixed rib area. Compared with triangular ribs, the T-shaped ribs showed up to a 65 % higher area-averaged Nusselt number and up to a 49.7% higher performance factor. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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17 pages, 6163 KiB

Open AccessArticle

Study on the Transient Characteristics of the Centrifugal Pump during the Startup Period with Assisted Valve

by Qiao Li, Xiang Ma, Peng Wu, Shuai Yang, Bin Huang and Dazhuan Wu

Processes 2020, 8(10), 1241; https://doi.org/10.3390/pr8101241 - 2 Oct 2020

Cited by 19 | Viewed by 3094

Abstract

The startup period, one of several transient operations in a centrifugal pump, takes note of some problems with these devices. Sometimes a transient high pressure and high flow rate over a very short period of time are required at the startup process. The [...] Read more.

The startup period, one of several transient operations in a centrifugal pump, takes note of some problems with these devices. Sometimes a transient high pressure and high flow rate over a very short period of time are required at the startup process. The pump^’s dynamic response is delayed because of the rotational inertia of the pump and motor. Our research focuses on how to get a large flow in a short time when the pump cannot meet the requirements alone without a large power driver. To achieve a strong response in the startup process, a ball valve is installed downstream of the pump. The pump^’s transient behavior during such transient operations is important and requires investigation. In this study, the external transient hydrodynamic performance and the internal flow of the pump during the transient startup period are studied by experiments and simulations. In order to find an appropriate matching method, different experiments were designed. The content and results of this paper are meaningful for performance prediction during the transient pump-valve startup period. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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15 pages, 8188 KiB

Open AccessArticle

Numerical Simulation of Axial Vortex in a Centrifugal Pump as Turbine with S-Blade Impeller

by Xiaohui Wang, Kailin Kuang, Zanxiu Wu and Junhu Yang

Processes 2020, 8(9), 1192; https://doi.org/10.3390/pr8091192 - 20 Sep 2020

Cited by 21 | Viewed by 4271

Abstract

Pump as turbines (PATs) are widely applied for recovering the dissipated energy of high-pressure fluids in several hydraulic energy resources. When a centrifugal pump operates as turbine, the large axial vortex occurs usually within the impeller flow passages. In view of the structure [...] Read more.

Pump as turbines (PATs) are widely applied for recovering the dissipated energy of high-pressure fluids in several hydraulic energy resources. When a centrifugal pump operates as turbine, the large axial vortex occurs usually within the impeller flow passages. In view of the structure and evolution of the vortex, and its effect on pressure fluctuation and energy conversion of the machine, a PAT with specific-speed 9.1 was analyzed based on detached eddy simulation (DES), and the results showed that vortices generated at the impeller inlet region, and the size and position of detected vortices, were fixed as the impeller rotated. However, the swirling strength of vortex cores changed periodically with double rotational frequency. The influence of vortices on pressure fluctuation of PAT was relatively obvious, deteriorating the operating stability of the machine evidently. In addition, the power loss near impeller inlet region was obviously heavy as the impact of large axial vortices, which was much more serious in low flow rate conditions. The results are helpful to realize the flow field of PAT and are instructive for blade optimization design. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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18 pages, 7582 KiB

Open AccessFeature PaperArticle

Optimization Design of a Two-Vane Pump for Wastewater Treatment Using Machine-Learning-Based Surrogate Modeling

by Sang-Bum Ma, Sung Kim and Jin-Hyuk Kim

Processes 2020, 8(9), 1170; https://doi.org/10.3390/pr8091170 - 17 Sep 2020

Cited by 16 | Viewed by 4418

Abstract

This paper deals with three-objective optimization, using machine-learning-based surrogate modeling to improve the hydraulic performances of a two-vane pump for wastewater treatment. For analyzing the internal flow field in the pump, steady Reynolds-averaged Navier-Stokes equations were solved with the shear stress transport turbulence [...] Read more.

This paper deals with three-objective optimization, using machine-learning-based surrogate modeling to improve the hydraulic performances of a two-vane pump for wastewater treatment. For analyzing the internal flow field in the pump, steady Reynolds-averaged Navier-Stokes equations were solved with the shear stress transport turbulence model as a turbulence closure model. The radial basis neural network model, which is an artificial neural network, was used as the surrogate model and trained to improve prediction accuracy. Three design variables related to the geometry of blade and volute were selected to optimize concurrently the objective functions with the total head and efficiency of the pump and size of the waste solids. The optimization results obtained by using the model showed highly accurate prediction values, and compared with the reference design, the optimum design provided improved hydraulic performances. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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19 pages, 6971 KiB

Open AccessArticle

Applications of an Improved Aerodynamic Optimization Method on a Low Reynolds Number Cascade

by Shuyi Zhang, Bo Yang, Hong Xie and Moru Song

Processes 2020, 8(9), 1150; https://doi.org/10.3390/pr8091150 - 14 Sep 2020

Cited by 9 | Viewed by 2607

Abstract

The effect of cascade aerodynamic optimization on turbomachinery design is very significant. However, for most traditional cascade optimization methods, aerodynamic parameters are considered as boundary conditions and rarely directly used as the optimization variables to realize optimization. Given this problem, this paper proposes [...] Read more.

The effect of cascade aerodynamic optimization on turbomachinery design is very significant. However, for most traditional cascade optimization methods, aerodynamic parameters are considered as boundary conditions and rarely directly used as the optimization variables to realize optimization. Given this problem, this paper proposes an improved cascade aerodynamic optimization method in which an incidence angle and nine geometric parameters are used to parameterize the cascade and one modified optimization algorithm is adopted to find the cascade with the optimal aerodynamic performance. The improved parameterization approach is based on the Non-Uniform Rational B-Splines (NURBS) method, the camber line superposing thickness distribution molding (CLSTDM) method, and the plane cascade design method. To rapidly and effectively find the cascade with the largest average lift-drag ratio within a certain range of incidence angles, modified particle swarm optimization combined with the modified very fast simulated annealing algorithm (PSO-MVFSA) is adopted. To verify the feasibility of the method, a cascade with NACA4412 and a practical cascade are optimized. It is found that the average lift-drag ratios of two optimal performance cascades are respectively increased by 13.38% and 15.21% in comparison to those of two original cascades. Meanwhile, through optimizing the practical cascade of the Blade D500, under different volume flow rates, the pressure coefficient of the optimized cascade is increased by an average of more than 6.12% compared to that of the prototype, and the average efficiency is increased by 11.15%. Therefore, this improved aerodynamic optimization method is reliable and feasible for the performance improvement of cascades with a low Reynolds number. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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20 pages, 7536 KiB

Open AccessArticle

Multi-Condition Optimization of Cavitation Performance on a Double-Suction Centrifugal Pump Based on ANN and NSGA-II

by Wenjie Wang, Yanpin Li, Majeed Koranteng Osman, Shouqi Yuan, Benying Zhang and Jun Liu

Processes 2020, 8(9), 1124; https://doi.org/10.3390/pr8091124 - 10 Sep 2020

Cited by 19 | Viewed by 3166

Abstract

Double-suction centrifugal pumps form an integral part of power plant systems in maintaining operational stability. However, there has been a common problem of achieving a better cavitation performance over a wider operating range because the traditional approach for impeller design often leads to [...] Read more.

Double-suction centrifugal pumps form an integral part of power plant systems in maintaining operational stability. However, there has been a common problem of achieving a better cavitation performance over a wider operating range because the traditional approach for impeller design often leads to the design effect not meeting the operational needs at off-design conditions. In addressing the problem, an optimization scheme was designed with the hub and shroud inlet angles of the double-suction impeller to minimize the suction performance at non-design flow conditions. A practical approach that speeds up the cavitation simulation process was applied to solve the experimental design, and a multi-layer feed forward artificial neural network (ANN) was combined with the non-dominated sorting genetic algorithm II to solve the multi-objective problem into three-dimensional (3D) Pareto optimal solutions that meet the optimization objective. At the design point, the suction performance was improved by 6.9%. At non-design flow conditions, the cavitation performance was improved by 3.5% at 1.2Q_d overload condition, 4% at 0.8Q_d, and 5% at 0.6Q_d. Additionally, there was significant reduction in the attached cavity distribution in the impeller and suction domains when the optimized model was compared to the original model at off-design points. Finally, the optimization established a faster method for a three-objective optimization of cavitation performance using ANN and 3D Pareto solutions. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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23 pages, 13767 KiB

Open AccessArticle

Research on the Application of Partial Similarity for a 1-1/2 Axial Compressor

by Hong Xie, Moru Song and Bo Yang

Processes 2020, 8(9), 1121; https://doi.org/10.3390/pr8091121 - 9 Sep 2020

Cited by 2 | Viewed by 2765

Abstract

In this paper, a method based on the partial similarity principle is presented to improve the aerodynamic design with low cost and high accuracy for a 1-1/2 axial compressor. By means of this method, during the process of a similar design, the machine [...] Read more.

In this paper, a method based on the partial similarity principle is presented to improve the aerodynamic design with low cost and high accuracy for a 1-1/2 axial compressor. By means of this method, during the process of a similar design, the machine Mach number and flowrate coefficient are maintained. The flow similarity between the prototype and its large-scaled alternative was observed, according to a detailed analysis of flow fields of rotor and stator. As well, the relative discrepancies of isentropic efficiency and pressure ratio between two models are 1.25% and 0.4% at design point, respectively. Besides, their performance curves agreed very well in the whole operating range. Moreover, it was also found that the flow similarity between the two models can be maintained under unsteady working conditions. Thereafter, in order to investigate the impact of stability optimization method on the similarity principle, casing treatment with single circumferential groove was applied to these two models. The flow similarity was still maintained and the flowrate near the stall was reduced about 1.1% with negligible deterioration of the overall performance. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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13 pages, 5039 KiB

Open AccessArticle

Numerical Study on the Influence of Step Casing on Cavitating Flows and Instabilities in Inducers with Equal and Varying Pitches

by Lu Yu, Haochen Zhang, Hui Chen, Zhigang Zuo and Shuhong Liu

Processes 2020, 8(9), 1103; https://doi.org/10.3390/pr8091103 - 4 Sep 2020

Cited by 5 | Viewed by 2110

Abstract

It is known that cavitating flow characteristics and instabilities in inducers can greatly impact the safety and stability of a liquid rocket. In this paper, step casing optimization design (Model OE and Model AE) was carried out for two three-bladed inducers with an [...] Read more.

It is known that cavitating flow characteristics and instabilities in inducers can greatly impact the safety and stability of a liquid rocket. In this paper, step casing optimization design (Model OE and Model AE) was carried out for two three-bladed inducers with an equal (Model O) and a varying pitch (Model A), respectively. The unsteady cavitation flow field and accompanied instabilities were studied via numerical simulations. Reductions of the cavity size and fluctuation were observed in cases with a step casing. A significant difference in cavity structures was seen as well. Referring to the pressure distributions on the blades and details of the flow field, the mechanism of cavitation suppression was revealed. This work provides a feasible and convenient method in engineering practice for optimizing the characteristic of the cavitating flow field and instabilities for the inducer. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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20 pages, 4664 KiB

Open AccessArticle

Research on the Dynamic Characteristics of Mechanical Seal under Different Extrusion Fault Degrees

by Yin Luo, Yakun Fan, Yuejiang Han, Weqi Zhang and Emmanuel Acheaw

Processes 2020, 8(9), 1057; https://doi.org/10.3390/pr8091057 - 30 Aug 2020

Cited by 7 | Viewed by 4888

Abstract

In order to explore the dynamic characteristics of the mechanical seal under different fault degrees, this paper selected the upstream pumping mechanical seal as the object of study. The research established the rotating ring-fluid film-stationary ring 3D model, which was built to analyze [...] Read more.

In order to explore the dynamic characteristics of the mechanical seal under different fault degrees, this paper selected the upstream pumping mechanical seal as the object of study. The research established the rotating ring-fluid film-stationary ring 3D model, which was built to analyze the fault mechanism. To study extrusion fault mechanism and characteristics, different dynamic parameters were used in the analysis process. Theoretical analysis, numerical simulation, and comparison were conducted to study the relationship between the fault degree and dynamic characteristics. It is the first time to research the dynamic characteristics of mechanical seals in the specific extrusion fault. This paper proved feasibility and effectiveness of the new analysis method. The fluid film thickness and dynamic characteristics could reflect the degree of the extrusion fault. Results show that the fluid film pressure fluctuation tends to be more intensive under the serious extrusion fault condition. The extrusion fault is more likely to occur when the fluid film thickness is too large or too small. Results illustrate the opening force is affected with the fluid film lubrication status and seal extrusion fault degrees. The fluid film stiffness would not always increase with the rotating speed growth. The seal fault would occur with the increasing of rotating speeds, and the leakage growth fluctuations could reflect the fault degree. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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11 pages, 2778 KiB

Open AccessArticle

Flow and Noise Characteristics of Centrifugal Fan in Low Pressure Environment

by Xilong Zhang, Yongliang Zhang and Chenggang Lu

Processes 2020, 8(8), 985; https://doi.org/10.3390/pr8080985 - 13 Aug 2020

Cited by 12 | Viewed by 5591

Abstract

The influence of low-pressure environment on centrifugal fan’s flow and noise characteristics was studied experimentally and numerically. A testbed was established to conduct the experimental test on the performance of a centrifugal fan, and the characteristic curve and power consumption curve of the [...] Read more.

The influence of low-pressure environment on centrifugal fan’s flow and noise characteristics was studied experimentally and numerically. A testbed was established to conduct the experimental test on the performance of a centrifugal fan, and the characteristic curve and power consumption curve of the fan under different pressure were obtained. Then the simulation model of the centrifugal fan was established, which was used to simulate the working process of centrifugal fan under different negative pressures. The results showed that the total pressure and static pressure of the fan decrease with the decrease of the ambient pressure. The total and static pressures of the fan under 60 kPa pressure condition decreased by 42.3% and 38.3%, respectively, compared with those of fan under the normal pressure. The main reason for this phenomenon is that the decrease of the environmental pressure leads to the decrease of air density. Besides, with the drop of environmental pressure, the sound pressure and sound power of the fan noise decreases. Full article

(This article belongs to the Special Issue CFD Based Researches and Applications for Fluid Machinery and Fluid Device)

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