This study presents a numerical simulation of the stall and surge in a centrifugal compressor and presents a description of the stall development in two different cases.The first case is for a compressor with vaneless...This study presents a numerical simulation of the stall and surge in a centrifugal compressor and presents a description of the stall development in two different cases.The first case is for a compressor with vaneless diffuser and the second is for a compressor with vaned diffuser of the vane island shape.The main aim of this study is to compare the flow characteristics and behavior for the two compressors near the surge operating condition and provide further understanding of the diffuser role when back flow occurs at surge.Results showed that for a location near the diffuser entrance,the amplitude of the static pressure fluctuations for the vaneless diffuser case is higher than that for the vaned diffuser case near surge condition.These pressure fluctuations in the case of the vaneless diffuser appear with a gradual decrease of the mean pressure value as a part of the surge cycle.While for the case of the vaned diffuser,the pressure drop during surge occurs faster than the case of the vaneless diffuser.Also,results indicated that during surge in the case of vaneless diffuser,there is a region with low velocity and back flow that appears as a layer connecting all impeller passages near shroud surface and this layer develops in size with time.On the other hand,for the case of vaned diffuser during surge,the low velocity regions appear in random locations in some passages and these regions expand with time towards the shroud surface.Results showed that during stall,the impeller passages are exposed to identical impact from stall cells in the case of vaneless diffuser while the stall effect varies from passage to another in the case of the vaned diffuser.展开更多
An effective method for delaying the dynamic stall of helicopter retreating blade by using the trailing edge flap has been established in this paper.The aerodynamic loads of blade section are calculated by using the L...An effective method for delaying the dynamic stall of helicopter retreating blade by using the trailing edge flap has been established in this paper.The aerodynamic loads of blade section are calculated by using the Leishman-Beddoes unsteady two-dimensional dynamic stall model and the aerodynamic loads of the trailing edge flap section are calculated by using the Hariharan-Leishman unsteady two-dimensional subsonic model.The analytical model for dynamic stall of elastic blade with the stiff trailing edge flap has been established.Adopting the aeroelastic analytical method and the Galerkin's method combined with numerical integration,the aeroelastic responses of rotor system in high-speed and high-load forward flight are solved.The mechanism for control of dynamic stall of retreating blade by using trailing edge flap has been presented.The numerical results indicate that the reasonably controlled swing of trailing edge flap can delay the dynamic stall of retreating blade under the same flight conditions.展开更多
The unsteady flow structure between rotor blade-to-blade passages in a three-stage axial flow compressor is experimentally investigated by detailed measurements of unsteady performance characteristics,casing wall pres...The unsteady flow structure between rotor blade-to-blade passages in a three-stage axial flow compressor is experimentally investigated by detailed measurements of unsteady performance characteristics,casing wall pressure fluctuations and their wavelet analyses.The main feature of the test compressor is a capacity tank facility connected in series to the compressor outlet in order to supply compression and/or expansion waves from downstream of the compressor.Research attention is focused on the post-stall characteristics of the surge and rotating stall which occur simultaneously.The influence of the compressor operating point on the unsteady performance curve shows that the surge cycle changes irregularly depending on the steady-state resistance characteristics,and the results of the wavelet analyses of the wall pressure fluctuations suggest that the surge cycle may selectively be determined by the rotating stall cell structure within the rotor cascade.展开更多
基金NPRP grant No.4-651-2-242 from the Qatar National Research Fund (a member of Qatar Foundation)
文摘This study presents a numerical simulation of the stall and surge in a centrifugal compressor and presents a description of the stall development in two different cases.The first case is for a compressor with vaneless diffuser and the second is for a compressor with vaned diffuser of the vane island shape.The main aim of this study is to compare the flow characteristics and behavior for the two compressors near the surge operating condition and provide further understanding of the diffuser role when back flow occurs at surge.Results showed that for a location near the diffuser entrance,the amplitude of the static pressure fluctuations for the vaneless diffuser case is higher than that for the vaned diffuser case near surge condition.These pressure fluctuations in the case of the vaneless diffuser appear with a gradual decrease of the mean pressure value as a part of the surge cycle.While for the case of the vaned diffuser,the pressure drop during surge occurs faster than the case of the vaneless diffuser.Also,results indicated that during surge in the case of vaneless diffuser,there is a region with low velocity and back flow that appears as a layer connecting all impeller passages near shroud surface and this layer develops in size with time.On the other hand,for the case of vaned diffuser during surge,the low velocity regions appear in random locations in some passages and these regions expand with time towards the shroud surface.Results showed that during stall,the impeller passages are exposed to identical impact from stall cells in the case of vaneless diffuser while the stall effect varies from passage to another in the case of the vaned diffuser.
基金supported by the National Natural Science Foundation of China (Grant No. 5107520)the Fundamental Research Funds for the Central Universities (Grant No. NP2011057)
文摘An effective method for delaying the dynamic stall of helicopter retreating blade by using the trailing edge flap has been established in this paper.The aerodynamic loads of blade section are calculated by using the Leishman-Beddoes unsteady two-dimensional dynamic stall model and the aerodynamic loads of the trailing edge flap section are calculated by using the Hariharan-Leishman unsteady two-dimensional subsonic model.The analytical model for dynamic stall of elastic blade with the stiff trailing edge flap has been established.Adopting the aeroelastic analytical method and the Galerkin's method combined with numerical integration,the aeroelastic responses of rotor system in high-speed and high-load forward flight are solved.The mechanism for control of dynamic stall of retreating blade by using trailing edge flap has been presented.The numerical results indicate that the reasonably controlled swing of trailing edge flap can delay the dynamic stall of retreating blade under the same flight conditions.
基金supported by a Grant-in-Aid for Scientific Research through grant number 20560171from Japanese Society for the Promotion of Science
文摘The unsteady flow structure between rotor blade-to-blade passages in a three-stage axial flow compressor is experimentally investigated by detailed measurements of unsteady performance characteristics,casing wall pressure fluctuations and their wavelet analyses.The main feature of the test compressor is a capacity tank facility connected in series to the compressor outlet in order to supply compression and/or expansion waves from downstream of the compressor.Research attention is focused on the post-stall characteristics of the surge and rotating stall which occur simultaneously.The influence of the compressor operating point on the unsteady performance curve shows that the surge cycle changes irregularly depending on the steady-state resistance characteristics,and the results of the wavelet analyses of the wall pressure fluctuations suggest that the surge cycle may selectively be determined by the rotating stall cell structure within the rotor cascade.
