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An axisymmetric characteristic model for enhancing prediction of centrifugal compressor characteristics

Chinese Journal of Aeronautics 2024年第4期37卷 203-215页

作者： Peng REN Xiangjun FANG Zeyu JIAO Ying HAN School of Energy and Power Engineering Beihang UniversityBeijing 100191China Guangdong Key Laboratory of Modern Control Technology Institute of Intelligent ManufacturingGuangdong Academy of SciencesGuangzhou 510070China

Rapid and accurate determination of compressor characteristic maps is essential for the initial design of centrifugal compressors in aircraft power systems. The accuracy of existing methodologies, which rely on combinations of loss models, varies significantly depending on the compressor's geometry and operational range. This variance necessitates substantial experimental or Computational Fluid Dynamics(CFD) data for coefficient calibration. To address this challenge, this study presents an axisymmetric characteristic model for compressor performance assessment. This model incorporates the factors of blade angle, meridional passage area, and the radial deflection angle of meridional streamlines of the compressor. These factors are derived from fundamental aerodynamic equations encompassing mass, momentum, and energy conservation of the compressor. In contrast to conventional one-dimensional approaches, the proposed method reduces the number of loss coefficients and more effectively accounts for the impact of geometric alterations on centrifugal compressor properties. Furthermore, the model reduces dependence on experimental and CFD data. Efficacy of the model is validated using experimental data from four distinct types of centrifugal compressors. Correlation analysis reveals that the model's coefficients can be expressed as functions of the ratio of the Reynolds number to the impeller tip speed. This ratio serves as a characteristic parameter for the design and optimization of centrifugal compressors. Consequently, the proposed method offers an efficient and accurate means for the quick computation of centrifugal compressor characteristics. This is of great significance for improving the efficiency of centrifugal compressors and reducing energy consumption.

关键词： centrifugal compressor Positive problem Characteristic prediction Aerodynamic characteristic Axisymmetric model

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Flow Loss Mechanism in a Supercritical Carbon Dioxide centrifugal compressor at Low Flow Rate Conditions

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Journal of Thermal Science 2024年第1期33卷 114-125页

作者： YANG Zimu JIANG Hongsheng ZHUGE Weilin CAI Ruikai YANG Mingyang CHEN Haoxiang QIAN Yuping ZHANG Yangjun State Key Laboratory of Automotive Safety and Energy Tsinghua UniversityBeijing 100084China School of Mechanical Engineering Shanghai Jiao Tong UniversityShanghai 200240China

With the advantages of high efficiency and compact structure,supercritical carbon dioxide(sC02)Brayton cycles have bright prospects for development in energy conversion field.As one of the core components of the power cycle,the centrifugal compressor tends to operate near the critical point(304.13 K,7.3773 MPa).Normally,the compressor efficiency increases as the inlet temperature decreases.When the inlet temperature is close to the critical point,the density increases sharply as the temperature decreases,which results in quickly decreasing of volume flow rate and efficiency reducing.The flow loss mechanism of the sCO_(2) compressor operating at low flow rate is studied in this paper.Computational fluid dynamics(CFD) simulations for sCO_(2)compressor were carried out at various inlet temperatures and various mass flow rates.When the sCO_(2)compressor operates at low volume flow rate,the flow loss is generated mainly on the suction side near the trailing edge of the blade.The flow loss is related to the counterclockwise vortexes generated on the suction side of the main blade.The vortexes are caused by the flow separation in the downstream region of the impeller passage,which is different from air compressors operating at low flow rates.The reason for this flow separation is that the effect of Coriolis force is especially severe for the sCO_(2) fluid,compared to the viscous force and inertial force.At lower flow rates,with the stronger effect of Coriolis force,the direction of relative flow velocity deviates from the direction of radius,resulting in its lower radial component.The lower radial relative flow velocity leads to severe flow separation on the suction side near the trailing edge of the main blade.

关键词： supercritical CO_(2) centrifugal compressor flow loss mechanism Coriolis force

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Stall Evolution Mechanism of a centrifugal compressor with a Wide-Long Vaneless Diffuser

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Journal of Thermal Science 2024年第3期33卷 899-913页

作者： ZHANG Lei KANG Jiacheng LANG Jinhua AN Guangyao ZHANG Qian WANG Longyao WANG Qifang Department of Power Engineering North China Electric Power UniversityBaoding071003China Hebei Key Laboratory of Low Carbon and High Efficiency Power Generation Technology North China Electric Power UniversityBaoding071003China

The rotating stall mechanism is of high importance for the stability of centrifugal compressors and thermal power cycles.The majority of research concerning this topic has concentrated on the initial stall phase.However,the evolution of stall cells in wide-long diffusers has not been comprehensively studied.In this paper,the causes of rotating stall in the wide-long diffuser and the three-dimensional evolution mechanism of stall cells during the stall process were thoroughly analyzed.During the stall induction phase,an annulus vortex structure was found in the reverse-flow zone near the hub side of the diffuser outlet,which was the initial form of stall cells.The whole evolution process of stall cells was divided into three phases as the flow rate decreased.During the initial stall phase,the dynamic equilibrium was built under effects of the impeller wake and the adverse pressure gradient.As a result,the number of stall cells was kept at seven and the size of stall cells remained constant.During the transition phase,the flow in the diffuser became unstable.Stall cells extended to the impeller outlet,and the effect of the wake flow was strengthened significantly.Stall cells started integrating and separating regularly.As a result,the number and propagation speed of stall cells varied periodically at a constant mass flow rate.During the deep stall phase,the size of stall cells remained unchanged,and the number of stall cells kept at one.This study has important practical guidance and engineering value for the high-efficiency design and safe operation of centrifugal compressors.

关键词： centrifugal compressor wide-long vaneless diffuser stall evolution mechanism wake flow

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Behavior of Vaneless Diffuser Stall in a centrifugal compressor

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Journal of Thermal Science 2022年第1期31卷 3-12页

作者： AGARI Yuki YAMAO Yoshifumi FUJISAWA Nobumichi OHTA Yutaka Department of Applied Mechanics and Aerospace Engineering Waseda UniversityTokyo 169-8555Japan

The rotating stall in a centrifugal compressor with a vaneless diffuser was investigated both experimentally and numerically with focus on the effect of the internal flow field within the impeller on the diffuser stall.Through numerical analysis,the boundary layer separation at the impeller outlet was found to play an important role in the expansion and rotation processes of the diffuser stall.In particular,the expanded boundary layer separation near the hub side at the outlet of the main blade(M.B.)suction surface passage was considered to be the main cause of the expansion and rotation processes.A longitudinal vortex existed at the throat of the M.B.passage,and the mass flow rate in the M.B.passage was significantly reduced by the blockage effect.In addition,the longitudinal vortex induced the rolling up flow near the hub side at the impeller exit.Thus,the boundary layer separation expanded.

关键词： centrifugal compressor vaneless diffuser pressure and velocity measurement CFD rotating stall

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Experimental investigation of characteristics of instability evolution in a centrifugal compressor

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Chinese Journal of Aeronautics 2023年第4期36卷 174-189页

作者： Hanzhi ZHANG Ce YANG Ben ZHAO Wei ZHAO Chenxing HU Wenli WANG Jianbing GAO Shijun SUN School of Mechanical Engineering Beijing Institute of TechnologyBeijing 100081China Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing 100190China School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China

The stable range of operation for the centrifugal compressor significantly influences the dynamic,economic,and environment-friendly characteristics of power systems.A deep understand-ing of the characteristics of instability evolution is necessary to improve the compressor stability.A centrifugal compressor equipped with a vaneless diffuser is experimentally investigated using high-response static-pressure measurements.The results obtained indicate that three typical rotational-speed ranges exist based on the different instability evolution characteristics,which reveals the var-ious impeller–diffuser matching behaviors over the entire speed range.At low-speed ranges((40%–75%)N_(max),N_(max)is the maximum rotational speed),the compressor exhibits stable,Rotating Insta-bility(RI),impeller stall(diffuser stall),and surge modes.The impeller stall mode is induced by RI and propagates downstream,resulting in the diffuser stall and compressor surge modes.In the medium-speed range((75%–85%)N_(max)),the compressor exhibits stable,diffuser stall,RI,and surge modes.In the high-speed range((85%–100%)N_(max)),the compressor exhibits stable,diffuser stall,and surge modes.The dominant instability position is shifted from the impeller to the diffuser as the rotational speed increases.Both the impeller and diffuser stall present an irregular sawtooth static-pressure wave and exhibit broadband frequency spectrum patterns.

关键词： centrifugal compressor Impellers Pressure measurement Rotating instability Stability Stall

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Applications of Additively Manufactured Adjustable Vaned Diffusers in centrifugal compressor

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Journal of Thermal Science 2022年第2期31卷 273-284页

作者： LIN Zhihua ZUO Zhitao LIANG Qi HOU Hucan GUO Wenbin CHEN Haisheng Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China National Energy Large Scale Physical Energy Storage Technologies R&D Center(Bijie) Bijie 551712China Nanjing Institute of Future Energy System IETCASNanjing 211135China

As a variable-condition adjustment technology,the adjustable vaned diffusers(AVDs)can expand the working flow range of the compressor in the compressed air energy storage(CAES)system and improve its aerodynamic performance.In order to investigate the regulatory mechanism of AVDs and capture the details of vane loading distribution for the diffuser design optimization,additively manufactured AVDs for testing in a centrifugal compressor closed test facility are designed and implemented.Firstly,the regulation law of AVDs was summarized by numerical analysis and experimental support,and the corresponding vane loading data was extracted for the distribution law.Then,based on the distribution characteristics,3D diffuser models were designed suitably for the adjustable components.Then,the laser selective melting(SLM)technology and die steel material 1.2709 were selected for metal printing according to the actual operating environment.Finally,performance testing and accuracy detection were performed on the finished test pieces,almost all inlet hole’s deviations were within the 0.3 mm tolerance.The research results indicated that additive manufacturing can significantly improve the accessibility of the internal flow channels of the diffuser,and derive the load of the blade on the pressure surface and suction surface in detail,also provide adjustable functions for variable operating conditions.It can not only break through the traditional processing bottleneck of the complicated internal flow channels of AVDs but also improve the design matching degree with adjustable components;simultaneously,it ensures high performance with high precision and effectively shortens the long lead time.

关键词： additive manufacturing centrifugal compressor adjustable vaned diffusers vane loading

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Numerical Investigation of a centrifugal compressor with a Pre-Compression Wedge Diffuser under High Subsonic Conditions

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Journal of Thermal Science 2020年第4期29卷 945-954页

作者： WANG Yi LI Qingkuo BAI Huan ZHOU Xueqi LU Xin’gen School of Aeronautics and Astronautics Central South UniversityChangsha 410083China AECC Hunan Aviation Powerplant Research Institute Hunan Key Laboratory of Turbomachinery on Small and Medium Areo-EngineZhuzhou 412002China Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing 100190China

As the total pressure ratio of centrifugal compressors increases, the diffuser inlet flow becomes highly subsonic or even supersonic, which causes additional shock loss. The shock loss leads the stage performance to drop greatly. Pre-compression is an efficient method for reducing shock loss and improving the stage performance. To study the effect of wedge diffusers with pre-compression blades on centrifugal compressor performance, wedge diffusers with various pre-compression angles, divergence angles and numbers of blades were designed and investigated via a numerical method. As a result, it is found that the compressor stage achieves high peak efficiency when the pre-compression angle ranges from 2.5° to 5.5° and when the divergence angle ranges from 7° to 9°. As the number of blades increases, the total pressure ratio and adiabatic efficiency of the compressor stage increase slightly, whereas the surge margin of the stage decreases.

关键词： wedge diffuser pre-compression high Subsonic centrifugal compressor

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Numerical Simulation Study on Influence of Equation of State on Internal Flow Field and Performance of S-CO_(2)compressor

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Journal of Thermal Science 2024年第3期33卷 888-898页

作者： ZHANG Lei YANG Zhenyu SUN Enhui ZHANG Qian AN Guangyao YUAN Wei Hebei Key Laboratory of Low Carbon and High Efficiency Power Generation Technology North China Electric Power UniversityBaoding071003China School of Energy Power&Mechanical EngineeringNorth China Electric Power UniversityBaoding071028China

The low power consumption of the near-critical compressor is the key factor for the high efficiency of supercritical CO_(2)Brayton cycle.In the numerical simulation of the compressor,the rapid changes in the thermophysical properties of the CO_(2)near the critical point make it difficult to capture the condensation phenomenon.This paper investigates the influence of fluid physical properties on the condensation phenomenon.Firstly,the differences in the physical properties of CO_(2)in the SRK EOS(equation of state),PR EOS,and SW EOS are compared.Then,the simulation of nozzles and compressors were carried out and discussed.Results show that the condensation positions predicted by the three EOSs are basically the same.Compared with SW EOS,the disparities between the maximum condensation mass fraction predicted by the PR and SRK EOSs is5.7%and 11.5%,and that of total pressure ratio is 0.3%and 3.8%,respectively.The results show that PR EOS can be considered for numerical simulation in engineering practice.Since its physical property calculation results are closer to the actual physical properties while the physical properties change more gently,it has considerable accuracy and numerical stability.

关键词： supercritical carbon dioxide equation of state centrifugal compressor numerical simulation condensation

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Numerical Investigation of the centrifugal compressor Stability Improvement by Half Vaned Low Solidity Diffusers

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Journal of Thermal Science 2021年第2期30卷 696-706页

作者： CHEN Siyue ZUO Shuguang WEI Kaijun School of Automotive Studies Tongji UniversityShanghai 201804China

centrifugal compressors for the fuel cell vehicles often operate near the surge line compared with the turbocharger compressors.Low solidity and half vaned diffusers are recognized as good ways to improve the stability of the centrifugal compressor.The presented work investigated four diffuser configurations (i.e.,the vaneless diffuser (VLD),full-height low solidity vaned diffuser (LSVD),hub-side half vaned diffuser (HVD) and shroud-side half vaned diffuser (SVD)) through steady-state and unsteady numerical simulations.The results show that the best performance is achieved by the LSVD,HVD and SVD at the design,surge and choke conditions.The flow rate at the surge operating point of the HVD has decreased by 15.53% compared with the LSVD,and 9.21% compared with the VLD.At near surge operating point,a longitudinal suction side passage vortex is formed on the hub of the LSVD and rotates as circumferential stall cells.A hairpin vortex is formed along the leading edge and is dragged by the main flow along the suction side as a local vortex shedding.The mechanism of the stability improvement by half vaned diffusers is that the tip leakage vortex migrates from the clearance side to the vane mounting side and replenishes the low-momentum zone on the mounting side.The best position where the half vaned diffuser should be mounted is based on the impeller outlet flow conditions,namely,the location of the wake region,where the meridional velocity and relative stagnation pressure is low.

关键词： centrifugal compressor low solidity diffuser half vaned diffuser flow control numerical simulation

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Influence of Tip Clearance on centrifugal compressor IGV Regulation and Improvement

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Journal of Thermal Science 2021年第3期30卷 1025-1033页

作者： SUN Qi WANG Huishe ZHU Junqiang JI Chunjun LI Chunyang YAO Ka Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing 100190China School of Energy and Power Engineering Dalian University of TechnologyDalian 116024China

In order to avoid collision with the end wall of the casing when the guide vane rotates around its own rotating axis in a centrifugal compressor,a circular gap will be left at the top of guide vane.Part of the gas flow through the clearance cannot be effectively regulated,and the tip clearance leakage vortex is formed,which has an impact on the mainstream and makes the compressor performance decline.In order to solve this problem,in this paper,three improved schemes of guide vane channel structure,including rectangular channel,cambered channel,and globular channel,were put forward,which can effectively improve the regulation ability of guide vane.Comparing these three improved channels with the original one,the stable operating range of the compressor was enlarged;the power consumption of the compressor was reduced and the efficiency of the compressor was improved.By comprehensive comparison,the cambered channel has better performance and is easier to process,which has potential to be widely used in practice.

关键词： centrifugal compressor inlet guide vane tip clearance

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