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Complex Flow in Fluid Machinery

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J: Thermal Management".

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 17874

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Special Issue Editors

Dr. Ning Zhang

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Guest Editor

School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China
Interests: complex flow in pumps; flow-induced pressure pulsations; multiphase flow

Prof. Dr. Bin Huang

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Guest Editor

Ocean College, Zhejiang University, Zhoushan 316021, China
Interests: fluid machinery; tidal turbine; ocean energy exploitation
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Yibin Li

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Guest Editor

School of Energy and Power Engineering, Lanzhou University of Technology, Lanzhou 730050, China
Interests: nuclear coolant reactor pump; unsteady flow in fluid machinery; gear pump

Special Issue Information

Dear Colleagues,

Fluid machineries, such as pumps, turbines and fans, are widely used in the industrial field, and it is difficult to imagine a modern society without them. Safe operation of fluid machinery is critical to ensure the entire industrial system is performing correctly. The stable operation of fluid machinery is closely related to the complex internal flow. An unsteady flow will induce pressure pulsation, alternative force acting on the shat, vibration and noise, so it is important to develop a deep understanding of the complex flow in fluid machinery.

This Special Issue aims to present and disseminate the most recent advances related to the complex flow of fluid machinery. These include, in particular, but not exclusively:

Flow instability;
Cavitation;
Flow control;
Pressure pulsations;
Flow-induced noise;
Multiphase flow;
Optimal design of fluid machinery.

Dr. Ning Zhang
Dr. Bin Huang
Prof. Dr. Yibin Li
Guest Editors

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Keywords

fluid machinery
complex flow
flow instability

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Published Papers (11 papers)

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Research

18 pages, 17062 KiB

Open AccessArticle

Research on Cavitation Performance of Bidirectional Integrated Pump Gate

by Huahuang Lai, Haoshu Wang, Zhen Zhou, Rongsheng Zhu and Yun Long

Energies 2023, 16(19), 6784; https://doi.org/10.3390/en16196784 - 23 Sep 2023

Cited by 2 | Viewed by 1132

Abstract

A pump gate is a device that controls the flow of water. It can stop the flood when it comes, drain the ponding gathered in the city, and improve the water circulation of the city. Traditional pumping stations require a large land area, and their pump houses and gates need to be designed separately. Furthermore, the construction period of traditional pumping stations is lengthy, and the maintenance costs are high. It can no longer meet the needs of modern cities for water environment management. Therefore, it is imperative to design a new type of pump gate. The integrated pump gate introduced in this paper is an integrated construction of gates and pumps to achieve automatic control and bidirectional operation. The research mainly consists of three parts: design of pumping station, theoretical analysis, and numerical calculation. By studying the unstable flow inside the integrated pump, the characteristics and the degree of cavitation occurrence are predicted. This can provide a reference basis for the optimal design and stability operation of the integrated pump gate. To investigate cavitation in an integrated pump gate, numerical simulations were performed for multiple operating conditions using the SST turbulence model. Constant numerical simulations of cavitation through numerical calculation, the characteristic curves of the integrated pump gate under forward and reverse operation at different flow points were obtained, and flow field analysis was performed for the model pump at 1.0 Q. The location and degree of cavitation occurrence were predicted. In this study, a preliminary analysis was conducted to investigate the influence of cavitation on the internal flow characteristics of integrated gate pumps. The research collected data related to cavitation characteristics, streamline patterns, and blade pressures. Additionally, the study explored the characteristics of cavitation phenomena, laying the foundation for the optimization of the design of bidirectional operation in integrated sluice gate pumps for future practical engineering applications. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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21 pages, 7490 KiB

Open AccessArticle

Analysis of the Complex Three-Dimensional Flow Structure in the Circulation Pump of the Flow-Making System Based on Delayed Detached Eddy Simulation

by Zhong Li, Lei Ding, Weifeng Gong, Dan Ni, Cunzhi Ma and Yanna Sun

Energies 2023, 16(15), 5643; https://doi.org/10.3390/en16155643 - 27 Jul 2023

Viewed by 1003

Abstract

As the core component of the flow-making system, the circulating pump has differences in its internal flow structure under different operating conditions, which affects the flow quality of the environmental simulation test area and the authenticity of marine environmental simulation. To explore the internal flow characteristics and outlet evolution characteristics of the circulating pump, this paper uses the DDES (delayed detached eddy simulation) method for numerical simulation. This paper combines BVF (boundary vorticity flow) diagnosis and the limit streamline method to analyze the evolution characteristics of the unstable flow area on the blade surface; it uses the Q criterion to identify the vortex structure inside the pump and analyze its evolution and development laws. Additionally, a quantitative analysis of the flow state of the circulating pump using flow uniformity indexes is performed. The results show that the surface of impeller blades is uniform under 1.0 Q_N. At 0.7 Q_N, the evolution process of the blade suction surface BVF is periodic, with a corresponding period of about 2/9 T (0.02 s). At 1.0 Q_N, the strength and scale of the separated vortices inside the guide vanes are minimized compared to other flow rates, and the scale and strength of the vortices show a decreasing trend along the outer normal direction. The evolution period of the separation vortex on the pressure surface of the guide vane is about 1/3 T (0.033 s) under 1.1 Q_N and the evolution period of the suction surface of the guide vane is about 2/3 T (0.067 s) under 0.7 Q_N. The flow uniformity indexes value downstream of the pump outlet under 1.0 Q_N are very close to the ideal value; with a corresponding value of Ϛ_i = 0.023,

\bar{θ}

= 89.94°, γ = 0.95, λ = 97.9%, the outflow can be approximately regarded as axial uniform flow. The research results can provide theoretical support for the further optimization design of circulating pumps and lay the foundation for the implementation of real systems. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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17 pages, 14113 KiB

Open AccessArticle

Numerical Simulation on Transient Pressure Pulsations and Complex Flow Structures of a Ultra-High-Speed Centrifugal Pump at Stalled Condition

by Zhenhua Zhou, Huacong Li, Jinbo Chen, Delin Li and Ning Zhang

Energies 2023, 16(11), 4476; https://doi.org/10.3390/en16114476 - 1 Jun 2023

Cited by 2 | Viewed by 1244

Abstract

A high-speed centrifugal pump is the key facility to deliver oil in an aero-engine. The stable operation is quite important to the safety of the engine. High-speed pump stability is essentially caused by the transient pressure pulsations excited by the complex flow within the pump, which needs to be clarified, especially for the pump under a rotating stall condition. In the current research, unsteady pressure pulsation and the corresponding flow distribution of the high-speed centrifugal pump are analyzed using the delayed detached-eddy simulation (DDES) method. Pressure signals within the pump are extracted by monitoring points. Results show that the dominant components in the pressure spectrum exhibit a significant difference at various flow rates, which locates at the blade passing frequency f_BPF under the rated working condition and deviates to five times the shaft frequency (5f_n) at the stalled condition. Such phenomenon is not observed in the normal centrifugal pump with low speed when using numerical and experiment methods, and usually the amplitude at f_BPF reaches the maximum. Under the stalled condition, the component at 0.2f_n is generated and considered as the rotating stall frequency, which is the same at different stalled flow rates. From velocity distribution, it is found that several blade channels are stalled as characterized by the large-scale separation bubbles, which are induced and triggered by the volute tongue. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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21 pages, 16348 KiB

Open AccessArticle

Experimental Study on PIV Measurement and CFD Investigation of the Internal Flow Characteristics in a Reactor Coolant Pump

by Dan Ni, Hongzhong Lu, Shiyuan Huang, Sheng Lu and Yang Zhang

Energies 2023, 16(11), 4345; https://doi.org/10.3390/en16114345 - 26 May 2023

Cited by 2 | Viewed by 1374

Abstract

The nuclear reactor coolant pump (RCP) is the core piece of equipment of a nuclear power plant (NPP). The energy performance and internal flow characteristics of RCPs are revealed by effective measurement methods, which are helpful to understand the flow mechanism of RCPs. The present work is intended to conduct an integrated study based on the energy performance test and Particle Image Velocimetry (PIV) flow-field non-contact measurement of the RCP. In addition, the prediction results of different turbulence models are compared with experimental results in detail. Through energy performance measurement and numerical calculation analysis, it can be found that various turbulence models have the ability to predict the performance of RCPs in engineering applications. At 0.8~1.2 Φ_d operating conditions, the maximum error is less than 10% and the minimum error is less than 0.1% by analyzing the energy performance of numerical calculations and experimental results. The PIV results show that the velocity of the discharge nozzle varies greatly from right (outlet of diffuser channel 2) to left (outlet of diffuser channel 12) due to different flow structures. Through the qualitative and quantitative comparison of the internal flow field, it can be concluded that, except for the low flow rate, compared with other computational models, the Realizable k-ε model can better predict the internal flow field of an RCP. The reasons for the experimental error and numerical calculation error are analyzed in detail, and the results can provide a reference for forecasting an RCP internal flow field with a special and complex structure. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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14 pages, 13639 KiB

Open AccessArticle

Investigation into Dynamic Pressure Pulsation Characteristics in a Centrifugal Pump with Staggered Impeller

by Dan Ni, Jinbo Chen, Feifan Wang, Yanjuan Zheng, Yang Zhang and Bo Gao

Energies 2023, 16(9), 3848; https://doi.org/10.3390/en16093848 - 29 Apr 2023

Cited by 5 | Viewed by 1784

Abstract

For the centrifugal pump, the rotor–stator interaction (RSI) induces high-energy pressure pulsation, which directly affects the stability of systems and equipment. Therefore, this work proposes a new staggered impeller structure to suppress high-energy pressure pulsation in centrifugal pumps. The original impeller blade is divided into two layers and is staggered at 10°, 20° and 30° to form a staggered impeller. The dynamic pressure pulsation characteristics of both the original impeller and the staggered impeller are predicted using large eddy simulation (LES). The results indicate that the uniform staggered arrangement of blades can significantly reduce the pressure pulsation energy in the pump by 54.69% under the design conditions, while also achieving the best performance. Even under off-design conditions, the pressure pulsation energy can still be effectively suppressed by the staggered blades. The study of the time–frequency domain of the monitoring points near the tongue found that the phase difference in the pressure fluctuation caused by the RSI between the staggered impeller and the tongue prevents the superposition of pressure pulsation energy and efficiently suppresses it in the pump. The results can provide a reference for optimizing low-vibration-noise pump impellers in engineering applications. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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20 pages, 9847 KiB

Open AccessArticle

Research on Cavitation Wake Vortex Structures Near the Impeller Tip of a Water-Jet Pump

by Yun Long, Mingyu Zhang, Zhen Zhou, Jinqing Zhong, Ce An, Yong Chen, Churui Wan and Rongsheng Zhu

Energies 2023, 16(4), 1576; https://doi.org/10.3390/en16041576 - 4 Feb 2023

Cited by 6 | Viewed by 1831

Abstract

Cavitation can cause noise in the water-jet pump. If cavitation occurs in the water-jet pump, the hydraulic components in the pump are prone to erosion. The surface erosion reduces energy delivery efficiency and increases maintenance costs. The decline in pump performance will lead to the instability of the entire energy system. In this paper, the cavitation flow structure of the water-jet pump is studied by the method of numerical simulation and experiment, which provides a reference for the prediction and improvement of cavitation. Based on the closed test platform, in order to reveal the physical process of cavitation evolution, high-speed photography is used to capture the complex cavitation flow phenomenon in the pump. After that, the cavitation vortex structure was further explored by numerical simulation. Through the simulation of the impeller blade tip leakage flow and the Tip Leakage Vortex Cavitation (TLVC) characteristics under different cavitation conditions, the flow mechanism of the impeller blade tip leakage flow and the separation vortex induced by the cavitation region under different cavitation conditions were revealed. The main factors affecting the development of the cavitation wake vortex structures were summarized. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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20 pages, 5931 KiB

Open AccessArticle

Multi-Parameter Optimization Analysis of Hydrodynamic Performance for Rim-Driven Thruster

by Yuanzhe Nie, Wu Ouyang, Zhuo Zhang, Gaoqiang Li and Ruicong Zheng

Energies 2023, 16(2), 891; https://doi.org/10.3390/en16020891 - 12 Jan 2023

Cited by 11 | Viewed by 2100

Abstract

The efficiency of rim-driven thrusters (RDT) has always been the focus of attention in the context of energy conservation and environmental protection. A multi-parameter collaborative optimization framework is proposed to improve the efficiency of RDT based on the response surface method (RSM). The common structural parameters of RDT, including pitch ratio, disk ratio and rake angle, are selected as design variables to carry out the Box–Behnken experimental design combined with the simulation data obtained through CFD calculations. The response surface second-order model is employed to evaluate the extent to which different parameters can affect the target variable and obtain the optimal hydraulic efficiency. The results show that the established model has high precision, good reproducibility and strong anti-interference ability. The influence of the pitch ratio, rake angle and disk ratio on open water efficiency decreases in sequence. Compared with the prototype RDT, the maximum efficiency of the optimized RDT is increased by 13.8%, and the surface pressure distribution and flow field characteristics are also significantly modified. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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20 pages, 8395 KiB

Open AccessArticle

Spatiotemporal Evolution and Fluctuation Characteristics of a Centrifugal Compressor under Near-Stall Conditions and High Mass-Flow Rate

by Kang Xiao, Zhengdao Wang, Hui Yang and Yikun Wei

Energies 2023, 16(1), 84; https://doi.org/10.3390/en16010084 - 21 Dec 2022

Viewed by 1629

Abstract

Spatiotemporal evolution and fluctuation characteristics of a centrifugal compressor are investigated by numerical simulation under near-stall conditions and with a high mass-flow rate. The large-eddy simulation (LES) for unsteady computations is implemented in the numerical simulation of unsteady flow. The internal flow physical mechanism of the centrifugal compressor is presented at a high mass-flow rate (1.1 Qn) and low mass-flow rate (0.8 Qn, near-stall). The spatiotemporal evolution of the velocity and streamline for the internal flow of the centrifugal compressor demonstrates that a lot of large-scale eddies near the tongue are transformed into small-scale ones at high mass-flow rates. High mass-flow rate resulted in excessive fluid velocity in the impeller. A large amount of impact loss massive backflow appears near the tip clearance, and boundary layer separation of the suction surface emerges firstly and at a low mass-flow rate. Considerable flow loss occurs in the centrifugal compressor at the two non-designed operating flow rates. Several pressure and velocity fluctuations in the key position of the compressor are presented by the two deviations from design conditions. The analysis of the fast Fourier transform (FFT) and amplitude spectrum show that the starting point of flow instability in the impeller is different for the two deviations from design-condition flow rates. Understanding the spatiotemporal evolution and spatiotemporal characteristics of pressure and velocity fluctuations can provide insight into the unsteady internal flow of centrifugal compressors at high mass-flow rates (1.1 Qn) and near-stall conditions (0.8 Qn). Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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21 pages, 19760 KiB

Open AccessArticle

Unsteady Study on the Influence of the Angle of Attack of the Blade on the Stall of the Impeller of the Double-Suction Centrifugal Pump

by Hao Wang, Yibin Li, Yunshan Kong, Shengfu Zhang and Teng Niu

Energies 2022, 15(24), 9528; https://doi.org/10.3390/en15249528 - 15 Dec 2022

Cited by 2 | Viewed by 1611

Abstract

In order to clearly show the influence on the rotating stall of the impeller of a double-suction centrifugal pump, this paper, using the numerical simulation method of Shear Stress Transform (SST), analyzes the effects of different inlet angles of the blade on hydraulic performance, internal flow field and pressure pulsation in the impeller. The results show that the small angle of attack of the blade inlet scheme can effectively suppress the impeller rotation stall and that the design point head and efficiency are increased by 6.4% and 5.7% respectively. This paper, using turbulence intensity to determine the generation of rotating stall, proposed that the average of turbulence intensity exceeding 2% is a necessary condition for the generation of rotating stall and discovered that the standard deviation of the big angle of attack of the scheme is always greater than that of the small angle being analyzed by the impeller pressure pulsation. The basic critical frequencies of blade inlet pressure pulsation with components of a low frequency is dominated by the impeller rotating frequency F₀ and its harmonic frequencies 2F₀, and 3F₀, but the basic critical frequencies of blade outlet pressure pulsation is governed by Blade Passing Frequency (BPF). The research results can provide some theoretical support for stall research and hydraulic performance optimization of a double-suction pump. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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25 pages, 9770 KiB

Open AccessArticle

Numerical Study on the Unsteady Flow Field Characteristics of a Podded Propulsor Based on DDES Method

by Ziyi Mei, Bo Gao, Ning Zhang, Yuanqing Lai and Guoping Li

Energies 2022, 15(23), 9117; https://doi.org/10.3390/en15239117 - 1 Dec 2022

Cited by 3 | Viewed by 1460

Abstract

The podded propulsor has gradually become an important propulsion device for high technology ships in recent years because of its characteristics of high maneuverability, high efficiency, low noise, and vibration. The performance of podded propulsor is closely related to its flow field. To study the unsteady flow field characteristics of podded propulsor, the DDES (delayed detached eddy simulation) method was used to carry out high-precision transient numerical simulations. Results showed that the pod has a significant influence on the unsteady flow field. The rotor–stator interaction between the propeller and pod can be observed, leading to the periodic fluctuation of thrust on the propeller. On the surface of pod, pressure distribution changes with time, leading to the difference of local lateral force. In the spatial region affected by the propeller wake flow, pressure distribution presents a spiral characteristic, both in the region far away from the pod, and in the region of the wake flow of strut and fin. The vortex structures of podded propulsor are complex since the interference of the pod. In addition to the tip, root and hub vortex, strut and fin vortices also occur. The vortices generated by the effect of mutual inductance between vortices are also discussed. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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15 pages, 7922 KiB

Open AccessArticle

Experimental Investigation on the Effect of the Staggered Impeller on the Unsteady Pressure Pulsations Characteristic in a Pump

by Dan Ni, Feifan Wang, Bo Gao, Yang Zhang and Shiyuan Huang

Energies 2022, 15(23), 8912; https://doi.org/10.3390/en15238912 - 25 Nov 2022

Cited by 3 | Viewed by 1470

Abstract

High−energy pressure pulsation induced by rotor−stator interaction (RSI) is the primary source of flow−induced vibration noise in the pump, affecting the pump’s stability and system operation. In order to find an effective method to suppress the pressure pulsation in the pump caused by RSI, a new staggered impeller is proposed in this paper, which can significantly suppress the pressure pulsation energy. The unsteady pressure pulsation characteristic of the original impeller and the staggered impeller scheme are measured and analyzed under different working flow conditions. The results show that although the hydraulic performance of the model pump decreases to a certain extent when the staggered impeller is used, the pressure pulsation energy in the pump decreases significantly. Under 0.8Q_N–1.2Q_N working flow conditions, the energy suppression effect of the blade passing frequency (f_bpf) amplitude is higher than 80% with the staggered impeller scheme. The Root Mean Square (RMS) values for distribution of pressure pulsation in different frequency bands varies greatly, and the pressure pulsation energy near the tongue is prominent. On a broader frequency band (0–6 f_bpf), the pressure pulsation energy of the staggered impeller scheme is smaller than that of the original impeller scheme. With the expansion of the frequency band, the pressure pulsation energy decreased steadily, with a minimum decrease of 37.33%. Full article

(This article belongs to the Special Issue Complex Flow in Fluid Machinery)

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