Special Issue "Turbomachinery: Theory, Design and Application"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 10317

Special Issue Editors

Prof. Minsuk Choi
E-Mail Website
Guest Editor
Department of Mechanical Engineering, Myongji University, Yongin 17058, Korea
Interests: turbomachinery; piezoelectric fan; synthetic jet; CFD
Special Issues, Collections and Topics in MDPI journals
Dr. Jin-Hyuk Kim
E-Mail Website
Guest Editor
1. Principal Researcher, Clean Energy R&D Department, Research Institute of Clean Manufacturing System, Korea Institute of Industrial Technology (KITECH), Chungcheongnam-do 31056, Korea
2. Associate Professor, Industrial technology (Green Process and Energy System Engineering), University of Science & Technology, Korea (UST), Daejeon 34113, Korea
Interests: design and optimization of fluid machinery; computational fluid dynamics (CFD); steady and unsteady numerical analyses; cavitation of hydraulic machines; flow measurements and experimental techniques
Special Issues, Collections and Topics in MDPI journals
Prof. Dazhuan Wu
E-Mail Website
Guest Editor
College of Energy Engineering, Zhejiang University, Hangzhou 310027, China
Interests: fluid machinery; pumps; fans; propeller

Special Issue Information

Dear Colleagues,

Turbomachinery is an essential part of the industrial field, and it is usually used for transporting fluids, extracting energy from flows, and cooling heated surfaces in many industrial sites and inside machines. Therefore, it is our pleasure to organize a Special Issue on turbomachinery in the prestigious journal Applied Sciences.

The title of this Special Issue is “Turbomachinery: Theory, Design and Application”, and all topics related to turbomachinery such as fans, compressors, pumps, turbines, wind turbines, etc. are within its scope. This Special Issue aims to present recent novel research trends and new innovative types of turbomachinery. Experiments and numerical simulations for turbomachinery are of course included in this Issue, and manuscripts for designing any type of turbomachinery are especially welcome. The following topics are examples of what this Issue will present.

  • Experiments and numerical simulations for turbomachinery;
  • Design and optimization of any type of turbomachinery;
  • Theoretical analysis for turbomachinery.

We hope you will consider participating in this Special issue.

Prof. Minsuk Choi
Prof. Dr. Jin-Hyuk Kim
Prof. Dazhuan Wu
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2300 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • turbomachinery
  • fan
  • compressor
  • pump
  • turbine
  • wind turbine

Published Papers (13 papers)

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Research

Article
Time-Marching Throughflow Analysis of Centrifugal Compressors with Boundary Conditions Based on Newton’s Method
Appl. Sci. 2022, 12(13), 6576; https://doi.org/10.3390/app12136576 - 29 Jun 2022
Viewed by 235
Abstract
The meridional distribution of the flow parameters inside the centrifugal compressor is of great importance to its overall performance, as well as its matching performance under a thermal cycle. A time-marching throughflow method for the off-design performance analysis of the centrifugal compressor is [...] Read more.
The meridional distribution of the flow parameters inside the centrifugal compressor is of great importance to its overall performance, as well as its matching performance under a thermal cycle. A time-marching throughflow method for the off-design performance analysis of the centrifugal compressor is described. The method is based on the strictly conservative throughflow-governing equations, and an improved method of boundary-condition enforcement is developed based on Newton’s method to achieve a robust and fast throughflow simulation. An inviscid blade force model was adopted to obtain the flow deflection inside the blade passage. Empirical loss models were integrated into the throughflow model to simulate the viscous force effects in the real three-dimensional flow. Two test cases are presented to validate the throughflow method by comparisons with the experimental data or CFD results, including the NASA low-speed centrifugal compressor (LSCC) and the Allison high-performance centrifugal compressor (HPCC). The simulation indicated that the developed enforcement method for the inlet and outlet boundary conditions significantly improves the computational robustness. For both the LSCC and HPCC cases, reasonable flow-parameter distribution was obtained and accurate overall characteristics were also predicted under the off-design conditions. The results indicated that the developed time-marching throughflow method is effective and efficient for the performance analysis of centrifugal compressors. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Analysis of Erosion Minimization for a Slurry Pump Using Discrete Phase Model Simulations
Appl. Sci. 2022, 12(3), 1597; https://doi.org/10.3390/app12031597 - 02 Feb 2022
Viewed by 407
Abstract
A slurry pump is a device used to transport slurry, which is a mixture of solids and liquids. The slurry pump is subjected to physical erosion, generally resulting from erosion by friction between the solid and liquid particles. This study aimed to analyze [...] Read more.
A slurry pump is a device used to transport slurry, which is a mixture of solids and liquids. The slurry pump is subjected to physical erosion, generally resulting from erosion by friction between the solid and liquid particles. This study aimed to analyze the effects of process parameters on the erosion wear of a throat bush, which is the main component of a slurry pump. The erosion rate density (E) was analyzed based on the process parameters, that is, the slurry particle diameter, rotation speed of the impeller, and gap between the impeller and the throat bush. The discrete phase model (DPM) of the slurry pump was simulated using the process parameters. These parameters were optimized to minimize the erosion rate density. The optimization method using design of experiments (DOE) to derive a specific location with the greatest influence of the design variables through the one-way layout method and optimize the response value at that location is a method that efficiently analyzes a large number of cases. The optimization results confirmed that the erosion rate density was reduced in the optimization model compared with the earlier model. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Influence of the Flexible Tower on Aeroelastic Loads of the Wind Turbine
Appl. Sci. 2021, 11(19), 8876; https://doi.org/10.3390/app11198876 - 24 Sep 2021
Cited by 1 | Viewed by 491
Abstract
The finite element discretization of a tower system based on the two-node Euler-Bernoulli beam is carried out by taking the cubic Hermite polynomial as the form function of the beam unit, calculating the structural characteristic matrix of the tower system, and establishing the [...] Read more.
The finite element discretization of a tower system based on the two-node Euler-Bernoulli beam is carried out by taking the cubic Hermite polynomial as the form function of the beam unit, calculating the structural characteristic matrix of the tower system, and establishing the wind turbine-nacelle-tower multi-degree-of-freedom finite element numerical model. The equation for calculating the aerodynamic load for any nacelle attitude angle is derived. The effect of the flexible tower vibration feedback on the aerodynamic load of the wind turbine is studied. The results show that, when the stiffness of the tower is large, the effect of having tower vibration feedback or not on the aeroelastic load of the wind turbine is small. For the more flexible tower system, wind-induced vibration time-varying feedback will cause larger aeroelastic load variations, especially the top of the tower overturning moment, thus causing a larger impact on the dynamic behavior of the tower downwind and crosswind. As the flexibility of the tower system increases, the interaction between tower vibration and pneumatic load is also gradually increasing. Taking into account the influence of flexible towers on the aeroelastic load of a wind turbine can help predict the pneumatic load of a wind turbine more accurately and improve the efficiency of wind energy utilization on the one hand and analyze the dynamic behavior of the flexible structure of a wind turbine more accurately on the other hand, which is extremely beneficial to the structural optimization of wind turbine. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Impact of Using Chevrons Nozzle on the Acoustics and Performances of a Micro Turbojet Engine
Appl. Sci. 2021, 11(11), 5158; https://doi.org/10.3390/app11115158 - 02 Jun 2021
Viewed by 1049
Abstract
This paper presents a study regarding the noise reduction of the turbojet engine, in particular the jet noise of a micro turbojet engine. The results of the measurement campaign are presented followed by a performances analysis which is based on the measured data [...] Read more.
This paper presents a study regarding the noise reduction of the turbojet engine, in particular the jet noise of a micro turbojet engine. The results of the measurement campaign are presented followed by a performances analysis which is based on the measured data by the test bench. Within the tests, beside the baseline nozzle other two nozzles with chevrons were tested and evaluated. First type of nozzle is foreseen with eight triangular chevrons, the length of the chevrons being L = 10 percentages from the equivalent diameter and an immersion angle of I = 0 deg. For the second nozzle the length and the immersion angle were maintained, only the chevrons number were increased at 16. The micro turbojet engine has been tested at four different regimes of speed. The engine performances were monitored by measuring the fuel flow, the temperature in front of the turbine, the intake air flow, the compression ratio, the propulsion force and the temperature before the compressor. In addition, during the testing, the vibrations were measured on axial and radial direction which indicate a normal functioning of the engine during the chevron nozzles testing. Regarding the noise, it was concluded that at low regimes the noise doesn’t presents any reduction when using the chevron nozzles, while at high regimes an overall noise reduction of 2–3 dB(A) was achieved. Regarding the engine performances, a decrease in the temperature in front of the turbine, compression ratio and the intake air and fuel flow was achieved and also a drop of few percent of the propulsion force. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Transient Analysis of Flow Unsteadiness and Noise Characteristics in a Centrifugal Compressor with a Novel Vaned Diffuser
Appl. Sci. 2021, 11(7), 3191; https://doi.org/10.3390/app11073191 - 02 Apr 2021
Cited by 4 | Viewed by 720
Abstract
The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor [...] Read more.
The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor on the flow-field unsteadiness and noise generation are investigated by solving the compressible, three-dimensional, transient Navier–Stokes equations. Diffuser vanes with various inclination angles of the leading edge from shroud-to-hub and hub-to-shroud are numerically modeled. The results show that the hub-to-shroud inclined leading edge improves the compressor performance (2.6%), and the proper inclination angle is effective to increase the stall margin (3.88%). In addition, in this study, the transient pressure variations and radiated noise prediction at the design operating point of the compressor are emphasized. The influences of the inclined leading edges on the pressure waves were captured in time/space domain with different convective velocities. The pressure fluctuation spectra are calculated to investigate the tonal blade passing frequency (BPF) noise, and it is shown that the applied inclination angles in the diffuser blades are effective, not only to improve the aerodynamic performance and stall margin, but also to reduce the BPF noise (7.6 dB sound pressure level reduction). Moreover, it is found that the diffuser vanes with inclination angles could suppress the separation regions and eddy structures inside the passages of the diffuser, which results in reduction of the overall sound pressure level and the broadband noise radiated from the compressor. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
3D Cavitation Shedding Dynamics: Cavitation Flow-Fluid Vortex Formation Interaction in a Hydrodynamic Torque Converter
Appl. Sci. 2021, 11(6), 2798; https://doi.org/10.3390/app11062798 - 21 Mar 2021
Cited by 4 | Viewed by 699
Abstract
Recent experiments have shown interactions between the cavitation and fluid vortex formation in a hydrodynamic torque converter. This study aimed to clarify the unsteady cavitation trigger mechanism and flow-induced vibration caused by turbulence–cavitation interactions. The mass transfer cavitation model and modified Reynolds-averaged Navier–Stokes [...] Read more.
Recent experiments have shown interactions between the cavitation and fluid vortex formation in a hydrodynamic torque converter. This study aimed to clarify the unsteady cavitation trigger mechanism and flow-induced vibration caused by turbulence–cavitation interactions. The mass transfer cavitation model and modified Reynolds-averaged Navier–Stokes k–ω model were used with a local density correction for turbulent eddy viscosity to investigate the cavitation structure in a hydrodynamic torque converter under various operating conditions. The model results were then validated against test data. The multi-block structured gridding technique was used to develop an orthogonally structured grid of a three-dimensional full-flow passage as an alternative analysis method for the cavitation flow. The results indicated that the re-entrant jet is the main cause of the shedding cavitation and breaking O-type cavitation. The re-entrant jet is driven by the reverse pressure gradient to move upstream towards the stator nose, and it lifts and splits the attached cavitation, which periodically induces shedding cavitation. When the cavitation was considered, the prediction error of the capacity constant was reduced from 13.23% to <5%. This work provides an insight into the cavitation–vortex interactions in a hydrodynamic torque converter, which can be used to improve the prediction accuracy of the hydrodynamic performance. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Flow Control of Radial Inlet Chamber and Downstream Effects on a Centrifugal Compressor Stage
Appl. Sci. 2021, 11(5), 2168; https://doi.org/10.3390/app11052168 - 01 Mar 2021
Cited by 1 | Viewed by 739
Abstract
Radial inlet chambers are widely used in various multistage centrifugal compressors, although they induce extra flow loss and inlet distortions. In this paper, the detailed flow characteristics inside the radial inlet chamber of an industrial centrifugal compressor have been numerically investigated for flow [...] Read more.
Radial inlet chambers are widely used in various multistage centrifugal compressors, although they induce extra flow loss and inlet distortions. In this paper, the detailed flow characteristics inside the radial inlet chamber of an industrial centrifugal compressor have been numerically investigated for flow control and performance improvement. First, the numerical results are validated against the experimental data, and flow conditions inside the inlet chambers with different structures are compared. They indicate that, in the non-guide vane scheme, sudden expansions, tangential flows and flow separations in the spiral and annular convergent channels are the major causes of flow loss and distortions, while using guide vanes could introduce additional flow impacts, separations and wakes. Based on the flow analysis, structure improvements have been carried out on the radial inlet chamber, and an average increase of 4.97% has been achieved in the inlet chamber efficiencies over different operating conditions. However, the results further reveal that the increases in the performance and overall flow uniformity just in the radial inlet chamber do not necessarily mean a performance improvement in the downstream components, and the distribution of the positive tangential velocity at the impeller inlet might be a more essential factor for the efficiency of the whole compressor. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Flow Field Analysis and Feasibility Study of a Multistage Centrifugal Pump Designed for Low-Viscous Fluids
Appl. Sci. 2021, 11(3), 1314; https://doi.org/10.3390/app11031314 - 01 Feb 2021
Cited by 3 | Viewed by 1100
Abstract
A multistage centrifugal pump is designed for pumping low-viscosity, highly volatile and flammable chemicals, including hydrocarbons, for high head requirements. The five-stage centrifugal pump consists of a double-suction impeller at the first stage followed by a twin volute. The impellers for stages two [...] Read more.
A multistage centrifugal pump is designed for pumping low-viscosity, highly volatile and flammable chemicals, including hydrocarbons, for high head requirements. The five-stage centrifugal pump consists of a double-suction impeller at the first stage followed by a twin volute. The impellers for stages two through five are single-suction impellers followed by diffuser vanes and return channel vanes. The analytical performance is calculated initially in the design stage by applying similarity laws to an existing scaled-down pump model designed for low flow rate applications. The proposed pump design is investigated using computational fluid dynamics tools to study its performance in design and off-design conditions for water as the base fluid. The design feasibility of the centrifugal pump is tested for other fluids, such as water at a high temperature and pressure, diesel and debutanized diesel. The pump design is found to be suitable for a variety of fluids and operating ranges. The losses in the pump are analyzed in each stage at the best efficiency point. The losses in efficiency and head are observed to be higher in the second stage than in other stages. The detailed flow behavior at the second stage is studied to identify the root cause of the losses. Design modifications are recommended to diminish the losses and improve the overall performance of the pump. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Influence of Spanwise Distribution of Impeller Exit Circulation on Optimization Results of Mixed Flow Pump
Appl. Sci. 2021, 11(2), 507; https://doi.org/10.3390/app11020507 - 06 Jan 2021
Cited by 4 | Viewed by 721
Abstract
The spanwise distribution of impeller exit circulation (SDIEC) has an important influence on the performance of the impeller. To quantitatively study the influence of SDIEC on optimization results, a comprehensive optimization system composed of the computational fluid dynamics, inverse design method, design of [...] Read more.
The spanwise distribution of impeller exit circulation (SDIEC) has an important influence on the performance of the impeller. To quantitatively study the influence of SDIEC on optimization results, a comprehensive optimization system composed of the computational fluid dynamics, inverse design method, design of experiment, surrogate model, and optimization algorithm was used to optimize a mixed flow pump impeller in two different cases. In the first case, the influence of SDIEC was ignored, while in the second case, the influence of SDIEC was considered. The result shows that the optimization upper limit can be further improved when the influence of SDIEC is considered in the optimization process. The pump efficiency of the preferred optimized impeller F1 obtained in the first case at 1.2Qdes, 1.0Qdes, and 0.8Qdes are increased by 6.48%, 2.41%, and 0.06%, respectively, over the baseline model. Moreover, the pump efficiency of the preferred optimized impeller S2 obtained in the second case further increased by 0.76%, 1.24%, and 1.21%, respectively, over impeller F1. Furthermore, the influence of SDIEC on the performance of the mixed flow pump is clarified by a comparative analysis of the internal flow field. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
A Coupled Effect Model of Two-Position Local Geometric Deviations on Subsonic Blade Aerodynamic Performance
Appl. Sci. 2020, 10(24), 8976; https://doi.org/10.3390/app10248976 - 16 Dec 2020
Cited by 1 | Viewed by 516
Abstract
The coupled aerodynamic performance influence of multiple deviations in the blade profile is a complex phenomena. In this paper, a high-pressure compressor rotor blade mid-span profile is studied with the design of experiments (DOE), numerical simulation and surrogate model to analyze the influence [...] Read more.
The coupled aerodynamic performance influence of multiple deviations in the blade profile is a complex phenomena. In this paper, a high-pressure compressor rotor blade mid-span profile is studied with the design of experiments (DOE), numerical simulation and surrogate model to analyze the influence of the deviations on the blade aerodynamic performance. The purpose of this work is to provide a new rapid evaluation approach for the blade aerodynamic performance under multiple geometric deviations influence. First, the Hicks-Henne function was used to model the local geometric deviations of the blade profile, and the blade aerodynamic performance was calculated by using the computational fluid dynamics tools. By analyzing the calculation results, the momentum thickness of the boundary layer, the deviations height and the distance between the deviations are combined into a coupled effect model. Then, the coupled effect model was used to rapidly evaluate the blade aerodynamic performance when the two-position local geometric deviations exist on the blade surface. Finally, the evaluated performance were compared with the results predicted by a high-precision surrogate model, which verifies the high accuracy of the coupled effect model in evaluating the positive incidence range of the blade profile. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Large Eddy Simulation of Film Cooling with Bulk Flow Pulsation: Comparative Study of LES and RANS
Appl. Sci. 2020, 10(23), 8553; https://doi.org/10.3390/app10238553 - 29 Nov 2020
Cited by 3 | Viewed by 969
Abstract
The effects of bulk flow pulsations on film cooling in gas turbine blades were investigated by conducting large eddy simulation (LES) and Reynolds-averaged Navier–Stokes simulation (RANS). The film cooling flow fields under 32 Hz pulsation in the mainstream from a cylindrical hole inclined [...] Read more.
The effects of bulk flow pulsations on film cooling in gas turbine blades were investigated by conducting large eddy simulation (LES) and Reynolds-averaged Navier–Stokes simulation (RANS). The film cooling flow fields under 32 Hz pulsation in the mainstream from a cylindrical hole inclined 35° to a flat plate at the average blowing ratio of M = 0.5 were numerically simulated. The LES results were compared to the experimental data of Seo, Lee, and Ligrani (1998) and Jung, Lee, and Ligrani (2001). The credibility of the LES results relative to the experimental data was demonstrated through a comparison of the time-averaged adiabatic film cooling effectiveness, time- and phase-averaged temperature contours, Q-criterion contours, time-averaged velocity profiles, and time- and phase-averaged Urms profiles with the corresponding RANS results. The adiabatic film cooling effectiveness predicted using LES agreed well with the experimental data, whereas RANS highly overpredicted the centerline effectiveness. RANS could not properly predict the injectant topology change in the streamwise normal plane, but LES reproduced it properly. In the case of the injectant trajectory, which greatly influences film cooling effectiveness, RANS could not properly predict the changes in the streamwise velocity peak due to flow pulsation, but they were predicted well with LES. RANS greatly underpredicted the streamwise velocity fluctuations, which determine the mixing of main flow and injectant, whereas LES prediction was close to the experimental data. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Design, Plant Test and CFD Calculation of a Turbocharger for a Low-Speed Engine
Appl. Sci. 2020, 10(23), 8344; https://doi.org/10.3390/app10238344 - 24 Nov 2020
Cited by 4 | Viewed by 758
Abstract
Various approaches and techniques are used to design centrifugal compressors. These are engineering one-dimensional and quasi-three-dimensional programs, as well as CFD Computational Fluid Dynamics (CFD) programs. The final judgment about the effectiveness of the design is given by testing the compressor or its [...] Read more.
Various approaches and techniques are used to design centrifugal compressors. These are engineering one-dimensional and quasi-three-dimensional programs, as well as CFD Computational Fluid Dynamics (CFD) programs. The final judgment about the effectiveness of the design is given by testing the compressor or its model. A centrifugal compressor for an internal combustion engine turbocharger was designed jointly by the Research Laboratory “Gas Dynamics of Turbomachines” of Peter the Great St. Petersburg Polytechnic University (SPbPU) and RPA (Research and Production Association) “Turbotekhnika”. To check its dimensionless characteristics, the compressor was tested with two geometrically similar impellers with a diameter of 175 (TKR 175E) and 140 mm (TKR 140E). The mathematical model of the Universal Modeling Method calculates the efficiency in the design mode for all tests of both compressors with an error of 0.89%, and the efficiency for the entire characteristic with an error of 1.55%. The characteristics of the TKR 140E compressor were calculated using the ANSYS commercial CFD software. For TKR-140E, a significant discrepancy in the value of the efficiency was obtained, but a good agreement in the area of operation, which was not achieved in previous calculations. According to the calculation, the work coefficient is overestimated by 9%, which corresponds to the results of previous calculations by the authors. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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Article
Evolution Characteristics of Separated Vortices and Near-Wall Flow in a Centrifugal Impeller in an Off-Designed Condition
Appl. Sci. 2020, 10(22), 8209; https://doi.org/10.3390/app10228209 - 19 Nov 2020
Cited by 2 | Viewed by 714
Abstract
Flow separation is undesirable and lowers the efficiency of centrifugal impellers. In this study, the evolution characteristics of separated vortices in a centrifugal impeller are studied under the off-designed flow rate condition. Unsteady Reynolds-Averaged Navier–Stokes (URANS) with standard k-ε turbulent model [...] Read more.
Flow separation is undesirable and lowers the efficiency of centrifugal impellers. In this study, the evolution characteristics of separated vortices in a centrifugal impeller are studied under the off-designed flow rate condition. Unsteady Reynolds-Averaged Navier–Stokes (URANS) with standard k-ε turbulent model is applied to simulate the alternating stall in the six-blade centrifugal impeller. We present and analyze the distributions of pressure gradient (either adverse or favorable) and skin friction coefficients on both sides of the blade for the stalled and unstalled passages to study the relationship between pressure gradient and separation of boundary layer flow. The evolution of skin friction coefficient is also presented at various axial cross sections. Numerical results reveal that, for the stalled passage, the increase in adverse pressure gradient on the pressure surface near the middle of the blade (S/S0 = 0.4) is much larger than that of the suction surface during a vortex formation cycle. The skin friction coefficient on the pressure surface also increases in magnitude sharply and the variation shows a peak-valley trend, while the coefficient on the suction surface increases slowly. Comparing the distribution of skin friction coefficient on the pressure surface of the same blade at different axial cross sections, it is found that the skin friction coefficient notably increases at S/S0 = 0.6 on the middle axial cross section (Z/b2 = 0.5). For the unstalled passage, both the pressure and suction surfaces produce favorable pressure gradients. The skin friction coefficient on the pressure surface shows an increasing trend around S/S0 = 0.5, and a large vortex can be seen at the exit of the impeller. The variation of skin friction coefficient on the suction surface is relatively mild; thus, the flow is relatively stable. It is clarified that the effect of adverse pressure gradient and wall shear stress jointly cause separation of the boundary layer; thus, the separated vortices are generated in the rotating impeller and deteriorate the performance of the impeller. Full article
(This article belongs to the Special Issue Turbomachinery: Theory, Design and Application)
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