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A special issue of Fluids (ISSN 2311-5521). This special issue belongs to the section "Mathematical and Computational Fluid Mechanics".

Deadline for manuscript submissions: closed (31 August 2024) | Viewed by 16591

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Special Issue Editors

Dr. Ling Zhou

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Guest Editor

China National Research Center of Pumps, Jiangsu University, Zhenjiang 212013, China
Interests: high-efficiency, high-lift submersible oil/submersible pump numerical simulation, optimization design and hydraulic model development; experimental measurement and control methods of pressure pulsation and axial force of multi-stage pumps; two-phase flow and abrasion and wear of fluid machinery

Dr. Wei Li

E-Mail Website
Co-Guest Editor

China National Research Center of Pumps, Jiangsu University, Zhenjiang 212013, China
Interests: design and optimization of fluid machinery; computational fluid dynamics (CFD); cavitation of pump; unsteady flow and control; flow measurements and experimental techniques
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Computational fluid dynamics (CFD) is widely used in the manufacturing of aerospace aircraft, petroleum, chemical, aerospace, water conservancy, agricultural irrigation and other industrial fields. However, the applications of CFD vary due to the diversity of their operating environments, which also have many problems, including multiphase flow, chemical reactions, heat transfer, etc. In the past several decades, more advanced computational models and appropriate methods to solve these problems have been the pursuit of scientists and engineers. Prof. Ramesh Agarwal is an outstanding representative, and developed the Wray–Agarwal turbulence model.

To celebrate the contributions of Prof. Ramesh Agarwal, we have created a new Special Issue. This Special Issue seeks high-quality original research articles with a focus on recent advances in computational research on aerospace design and fluid dynamics. Original research and review articles are welcome.

Potential topics include but are not limited to the following:

Airfoil;
Aerospace materials;
Control of unsteady flow in fluid machinery;
Application of new turbulence models, such as the Wray–Agarwal model;
Multi-phase flow in fluid machinery;
Turbulence in fluid machinery;
Rotating stall;
Fluid–solid interaction;
Drag reduction;
Incompressible and compressible fluids;
Other relevant topics.

Dr. Ling Zhou
Dr. Wei Li
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

fluid machinery
computational fluid dynamics
turbulent flow

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Published Papers (11 papers)

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Research

15 pages, 2451 KiB

Open AccessArticle

A Review of Biomechanical Studies of Heart Valve Flutter

by Lu Chen, Zhuo Zhang, Tao Li and Yu Chen

Fluids 2024, 9(11), 254; https://doi.org/10.3390/fluids9110254 - 29 Oct 2024

Viewed by 429

Abstract

This paper reviews recent biomechanical studies on heart valve flutter. The function of the heart valves is essential for maintaining effective blood circulation. Heart valve flutter is a kind of small vibration phenomenon like a flag fluttering in the wind, which is related to many factors such as a thrombus, valve calcification, regurgitation, and hemolysis and material fatigue. This vibration phenomenon is particularly prevalent in valve replacement patients. The biomechanical implications of flutter are profound and can lead to micro-trauma of valve tissue, accelerating its degeneration process and increasing the risk of thrombosis. We conducted a systematic review along with a critical appraisal of published studies on heart valve flutter. In this review, we summarize and analyze the existing literature; discuss the detection methods of frequency and amplitude of heart valve flutter, and its potential effects on valve function, such as thrombosis and valve degeneration; and discuss some possible ways to avoid flutter. These findings are important for optimizing valve design, diagnosing diseases, and developing treatment strategies. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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30 pages, 8574 KiB

Open AccessArticle

Finite Element Analysis and Computational Fluid Dynamics for the Flow Control of a Non-Return Multi-Door Reflux Valve

by Xolani Prince Hadebe, Bernard Xavier Tchomeni Kouejou, Alfayo Anyika Alugongo and Desejo Filipeson Sozinando

Fluids 2024, 9(10), 238; https://doi.org/10.3390/fluids9100238 - 9 Oct 2024

Viewed by 769

Abstract

This paper presents a comprehensive analysis of a multi-door check valve using computational fluid dynamics (CFD) and finite element analysis (FEA) to evaluate flow performance under pressure test conditions, with an emphasis on its ability to prevent backflow. Check valves are essential components in various industries, ensuring fluid flow in one direction only while preventing reverse flow. The non-return multi-door reflux valve is increasingly preferred due to its superior backflow prevention, fluid control, and effective flow regulation. Rigorous testing under varying pressure conditions is essential to ensure that these valves perform optimally. This study uses CFD and FEA simulations to evaluate the structural integrity and flow characteristics of the valve, including pressure drop, flow velocity, backflow prevention effectiveness, and flow coefficient. A high-fidelity 3D model was created to simulate the valve’s behavior under various conditions, analyzing the effects of parameters such as the number of doors, their orientation, geometry, and operating conditions. The CFD results demonstrated a significant reduction in backflow and pressure drop across the valve. However, localized turbulence and flow separation near the valve doors, particularly under partially open conditions, have raised concerns about potential wear. The velocity profiles indicated a uniform distribution at full opening with laminar velocity profiles and minimal resistance to flow. The results of the FEA showed that the stresses induced by the fluid forces were below critical levels, with the highest stress concentrations observed around the hinge points of the valve doors. Although the valve structure remained intact under normal operating conditions, some areas may have required reinforcement to ensure long-term durability. Combined CFD and FEA analyses demonstrated that the valve effectively preserves system integrity, prevents backflow, and maintains consistent performance under various pressure and flow conditions. These findings provide valuable insights into design improvements, performance optimization, and enhancing the efficiency and reliability of reflux valve systems in industrial applications. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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20 pages, 6955 KiB

Open AccessArticle

Flow Performance Analysis of Non-Return Multi-Door Reflux Valve: Experimental Case Study

by Xolani Prince Hadebe, Bernard Xavier Tchomeni Kouejou, Alfayo Anyika Alugongo and Desejo Filipeson Sozinando

Fluids 2024, 9(9), 213; https://doi.org/10.3390/fluids9090213 - 12 Sep 2024

Cited by 1 | Viewed by 764

Abstract

Non-return multi-door reflux valves are essential in fluid control systems to prevent reverse flow and maintain system integrity. This study experimentally analyzes the flow performance of multi-door check valves under different operating conditions, focusing on pressure testing and evaluating their effectiveness in preventing backflow. A wide-ranging experimental setup was designed and implemented to simulate real-world scenarios, facilitating accurate measurement of flow rates, pressure differences, and valve response times. The collected experimental data were analyzed to evaluate the valve’s performance in terms of flow capacity, pressure drop, and hydraulic efficiency. Additionally, the effects of factors such as valve size, valve configuration, and fluid properties (water) on performance were considered. It was found that the non-return multi-door reflux valve has been proven effective and reliable in preserving system integrity and maintaining unidirectional flow at the same time during pressure testing. It exhibits no backflow, remains stable and constant across varied flow conditions, and demonstrates a low pressure drop and high flow capacity, making it suitable for critical pressure testing applications. The response curve revealed that valve opening takes longer to reach higher flow rates than closing, indicating pressure instability during transition periods. This non-linear relationship indicates possible irregularities in pressure drop response to flow rate changes, highlighting potential areas for further investigation. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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28 pages, 15256 KiB

Open AccessArticle

A Computational Analysis of Turbocharger Compressor Flow Field with a Focus on Impeller Stall

by Deb K. Banerjee, Ahmet Selamet and Pranav Sriganesh

Fluids 2024, 9(7), 162; https://doi.org/10.3390/fluids9070162 - 17 Jul 2024

Viewed by 762

Abstract

Understanding the flow instabilities encountered by the turbocharger compressor is an important step toward improving its overall design for performance and efficiency. While an experimental study using Particle Image Velocimetry was previously conducted to examine the flow field at the inlet of the turbocharger compressor, the present work complements that effort by analyzing the flow structures leading to stall instability within the same impeller. Experimentally validated three-dimensional computational fluid dynamics predictions are carried out at three discrete mass flow rates, including 77 g/s (stable, maximum flow condition), 57 g/s (near peak efficiency), and 30 g/s (with strong reverse flow from the impeller) at a fixed rotational speed of 80,000 rpm. Large stationary stall cells were observed deep within the impeller at 30 g/s, occupying a significant portion of the blade passage near the shroud between the suction surface of the main blades and the pressure surface of the splitter blades. These stall cells are mainly created when a substantial portion of the inlet core flow is unable to follow the impeller’s axial to radial bend against the adverse pressure gradient and becomes entrained by the reverse flow and the tip leakage flow, giving rise to a region of low-momentum fluid in its wake. This phenomenon was observed to a lesser extent at 57 g/s and was completely absent at 77 g/s. On the other hand, the inducer rotating stall was found to be most dominant at 57 g/s. The entrainment of the tip leakage flow by the core flow moving into the impeller, leading to the generation of an unstable, wavy shear layer at the inducer plane, was instrumental in the generation of rotating stall. The present analyses provide a detailed characterization of both stationary and rotating stall cells and demonstrate the physics behind their formation, as well as their effect on compressor efficiency. The study also characterizes the entropy generation within the impeller under different operating conditions. While at 77 g/s, the entropy generation is mostly concentrated near the shroud of the impeller with the core flow being almost isentropic, at 30 g/s, there is a significant increase in the area within the blade passage that shows elevated entropy production. The tip leakage flow, its interaction with the blades and the core forward flow, and the reverse flow within the impeller are found to be the major sources of irreversibilities. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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27 pages, 5143 KiB

Open AccessArticle

Computational Fluid Dynamics Prediction of External Thermal Loads on Film-Cooled Gas Turbine Vanes: A Validation of Reynolds-Averaged Navier–Stokes Transition Models and Scale-Resolving Simulations for the VKI LS-94 Test Case

by Simone Sandrin, Lorenzo Mazzei, Riccardo Da Soghe and Fabrizio Fontaneto

Fluids 2024, 9(4), 91; https://doi.org/10.3390/fluids9040091 - 15 Apr 2024

Cited by 1 | Viewed by 1684

Abstract

Given the increasing role of computational fluid dynamics (CFD) simulations in the aerothermal design of gas turbine vanes and blades, their rigorous validation is becoming more and more important. This article exploits an experimental database obtained by the von Karman Institute (VKI) for Fluid Dynamics for the LS-94 test case. This represents a film-cooled transonic turbine vane, investigated in a five-vane linear cascade configuration under engine-like conditions in terms of the Reynolds number and Mach number. The experimental characterization included inlet freestream turbulence measured with hot-wire anemometry, aerodynamic performance assessed with a three-hole pressure probe in the downstream section, and vane convective heat transfer coefficient distribution determined with thin-film thermometers. The test matrix included cases without any film-cooling injection, pressure-side injection, and suction-side injection. The CFD simulations were carried out in Ansys Fluent, considering the impact of mesh sizing and steady-state Reynolds-Averaged Navier-Stokes (RANS) transition modelling, as well as more accurate transient scale-resolving simulations. This work provides insight into the advantages and drawbacks of such approaches for gas turbine hot-gas path designers. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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21 pages, 6496 KiB

Open AccessArticle

Characterization of Oscillatory Response of Light-Weight Wind Turbine Rotors under Controlled Gust Pulses

by Fernando Ponta, Alayna Farrell, Apurva Baruah and North Yates

Fluids 2024, 9(4), 83; https://doi.org/10.3390/fluids9040083 - 26 Mar 2024

Viewed by 1307

Abstract

Given the industry-wide trend of continual increases in the size of utility-scale wind turbines, a point will come where reductions will need to be made in terms of the weight of the turbine’s blades to ensure they can be as long as needed without sacrificing structural stability. One such technique that may be considered is to decrease the material used for the shell and spar cap. While this will solve the weight issue, it creates a new one entirely—less material for the shell and spar cap will in turn create blades that are more flexible than what is currently used. This article aims to investigate how the oscillatory response of light-weight wind turbine rotors is affected by these flexibility changes. The object of our study is the Sandia National Lab National Rotor Testbed (SNL-NRT) wind turbine, which the authors investigated in the course of a research project supported by SNL. Using a reduced-order characterization (ROC) technique based on controlled gust pulses, introduced by the authors in a previous work, the aeroelastic dynamics of the NRT’s original baseline blade design and several of its flexible variations were studied via numerical simulations employing the CODEF multiphysics suite. Results for this characterization are presented and analyzed, including a generalization of the ROC of the SNL-NRT oscillatory dynamics to larger machines with geometrical similarity. The latter will prove to be valuable in terms of extrapolating results from the present investigation and other ongoing studies to the scale of current and future commercial machines. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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18 pages, 7764 KiB

Open AccessArticle

Numerical Approach Based on Solving 3D Navier–Stokes Equations for Simulation of the Marine Propeller Flow Problems

by Andrey Kozelkov, Vadim Kurulin, Andrey Kurkin, Andrey Taranov, Kseniya Plygunova, Olga Krutyakova and Aleksey Korotkov

Fluids 2023, 8(11), 293; https://doi.org/10.3390/fluids8110293 - 31 Oct 2023

Cited by 1 | Viewed by 1921

Abstract

The report presents the approach implemented in the Russian LOGOS software package for the numerical simulation of the marine propeller flow problems using unstructured computational meshes automatically generated by the mesh generator. This approach includes a computational model based on the Navier–Stokes equation system and written with respect to the physical process: the turbulent nature of flow with transient points is accounted using the Reynolds Averaged Navier–Stokes method and the k–ω SST model of turbulence by Menter along with the γ–Re_θ (Gamma Re Theta) laminar-turbulent transition model; the Volume of Fluid method supplemented with the Schnerr–Sauer cavitation model is used to simulate the cavitation processes; a rotating propeller is simulated by a moving computational mesh and the GGI method to provide conformity of the solutions on adjacent boundaries of arbitrarily-shaped unstructured meshes of the two domains. The specific features of the numerical algorithms in use are described. The method validation results are given; they were obtained because of the problems of finding the performance curves of model-scale propellers in open water, namely the problems of finding the performance of propellers KP505 and IB without consideration of cavitation and the performance of propellers VP1304 and C5 under cavitation conditions. The paper demonstrates that the numerical simulation method presented allows for obtaining sufficiently accurate results to predict the main hydrodynamic characteristics for most modes of operation of the propellers. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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20 pages, 3488 KiB

Open AccessArticle

Numerical Simulation of the Conjugate Heat Transfer of a “Fluid–Solid Body” System on an Unmatched Grid Interface

by Aleksey Korotkov, Andrey Kozelkov, Andrey Kurkin, Robert Giniyatullin and Sergey Lashkin

Fluids 2023, 8(10), 266; https://doi.org/10.3390/fluids8100266 - 27 Sep 2023

Cited by 1 | Viewed by 1482

Abstract

Recently, when modeling transient problems of conjugate heat transfer, the independent construction of grid models for fluid and solid subdomains is increasingly being used. Such grid models, as a rule, are unmatched and require the development of special grid interfaces that match the heat fluxes at the interface. Currently, the most common sequential approach to modeling problems of conjugate heat transfer requires the iterative matching of boundary conditions, which can significantly slow down the process of the convergence of the solution in the case of modeling transient problems with fast processes. The present study is devoted to the development of a direct method for solving conjugate heat transfer problems on grid models consisting of inconsistent grid fragments on adjacent boundaries in which, in the general case, the number and location of nodes do not coincide. A conservative method for the discretization of the heat transfer equation by the direct method in the region of inconsistent interface boundaries between liquid and solid bodies is proposed. The proposed method for matching heat fluxes at mismatched boundaries is based on the principle of forming matched virtual boundaries, proposed in the GGI (General Grid Interface) method. A description of a numerical scheme is presented, which takes into account the different scales of cells and the sharply different thermophysical properties at the interface between liquid and solid media. An algorithm for constructing a conjugate matrix, the form of matrix coefficients responsible for conjugate heat transfer, and methods for calculating them are described. The operability of the presented method is demonstrated by the example of calculating conjugate heat transfer problems, the grid models of which consist of inconsistent grid fragments. The use of the direct conjugation method makes it possible to effectively solve both stationary and non-stationary problems using inconsistent meshes, without the need to modify them in the conjugation region within a single CFD solver. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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15 pages, 7207 KiB

Open AccessArticle

Modelling of Peristaltic Pumps with Respect to Viscoelastic Tube Material Properties and Fatigue Effects

by Marco Hostettler, Raphael Grüter, Simon Stingelin, Flavio De Lorenzi, Rudolf M. Fuechslin, Cyrill Jacomet, Stephan Koll, Dirk Wilhelm and Gernot K. Boiger

Fluids 2023, 8(9), 254; https://doi.org/10.3390/fluids8090254 - 19 Sep 2023

Viewed by 2575

Abstract

Peristaltic pump technology is widely used wherever relatively low, highly accurately dosed volumetric flow rates are required and where fluid contamination must be excluded. Thus, typical fields of application include food, pharmaceuticals, medical technology, and analytics. In certain cases, when applied in conjunction with polymer-based tubing material, supplied peristaltic flow rates are reported to be significantly lower than the expected set flow rates. Said flow rate reductions are related to (i) the chosen tube material, (ii) tube material fatigue effects, and (iii) the applied pump frequency. This work presents a fast, dynamic, multiphysics, 1D peristaltic pump solver, which is demonstrated to capture all qualitatively relevant effects in terms of peristaltic flow rate reduction within linear peristaltic pumps. The numerical solver encompasses laminar fluid dynamics, geometric restrictions provided by peristaltic pump operation, as well as viscoelastic tube material properties and tube material fatigue effects. A variety of validation experiments were conducted within this work. The experiments point to the high degree of quantitative accuracy of the novel software and qualify it as the basis for elaborating an a priori drive correction. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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26 pages, 14053 KiB

Open AccessArticle

Improving Pump Characteristics through Double Curvature Impellers: Experimental Measurements and 3D CFD Analysis

by Alfredo M. Abuchar-Curi, Oscar E. Coronado-Hernández, Jairo Useche, Verónica J. Abuchar-Soto, Argemiro Palencia-Díaz, Duban A. Paternina-Verona and Helena M. Ramos

Fluids 2023, 8(8), 217; https://doi.org/10.3390/fluids8080217 - 27 Jul 2023

Viewed by 1895

Abstract

The outlet angle and shape of impeller blades are important parameters in centrifugal pump design. There is a lack of detailed studies related to double curvature impellers in centrifugal pumps in the current literature; therefore, an experimental and numerical analysis of double curvature impellers was performed. Six impellers were made and then assessed in a centrifugal pump test bed and simulated via 3D CFD simulation. The original impeller was also tested and simulated. One of the manufactured impellers had the same design as the original, and the other five impellers had a double curvature. Laboratory tests and simulations were conducted with three rotation speeds: 1400, 1700, and 1900 RPM. Head and performance curve equations were obtained for the pump–engine unit based on the flow of each impeller for the three rotation speeds. The results showed that a double curvature impeller improved pump head by approximately 1 m for the range of the study and performance by about 2% when compared to basic impeller. On the other hand, it was observed that turbulence models such as k-ε and SST k-ω reproduced similar physical and numerical results. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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24 pages, 5981 KiB

Open AccessArticle

Two-Fluid Large-Eddy Simulation of Two-Phase Flow in Air-Sparged Hydrocyclone

by Mustafa Bukhari, Hassan Fayed and Saad Ragab

Fluids 2023, 8(5), 139; https://doi.org/10.3390/fluids8050139 - 25 Apr 2023

Cited by 1 | Viewed by 1787

Abstract

The two-fluid (Euler–Euler) model and large-eddy simulation are used to compute the turbulent two-phase flow of air and water in a cyclonic flotation device known as an Air-Sparged Hydrocyclone (ASH). In the operation of ASH, air is injected through a porous cylindrical wall. The study considers a 48 mm diameter hydrocyclone and uses a block-structured fine mesh of 10.5 million hexagonal elements. The air-to-water injection ratio is 4, and a uniform air bubble diameter of 0.5 mm is specified. The flow field in ASH was investigated for the inlet flow rate of water of 30.6 L/min at different values of underflow exit pressure. The current simulations quantify the effects of the underflow exit pressure on the split ratio and the overall flow physics in ASH, including the distribution of the air volume fraction, water axial velocity, tangential velocity, and swirling-layer thickness. The loci of zero-axial velocity surfaces were determined for different exit pressures. The water split ratio through the overflow opening varies with underflow exit pressure as 6%, 8%, 16%, and 26% for 3, 4, 5, and 6 kPa, respectively. These results indicate that regulating the pressure at the underflow exit can be used to optimize the ASH’s performance. Turbulent energy spectra in different regions of the hydrocyclone were analyzed. Small-scale turbulence spectra at near-wall points exhibit

f^{- 4}

law, where f is frequency. Whereas for points at the air-column interface, the energy spectra show an inertial subrange

f^{- 5 / 3}

followed by a dissipative range of

f^{- 7}

law. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)

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