The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines. The compressor is composed of inlet guide vanes, a backswept splittered un- ...The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines. The compressor is composed of inlet guide vanes, a backswept splittered un- shrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes. Previous numerical simulations revealed a particular S-shape pressure rise characteristic at partial rotation speed and predicted an alternate flow pattern in the vaned radial diffuser at low mass flow rate. This alternate flow pattern involves two adjacent vane passages. One passage exhibits very low momentum and a low pressure recovery, whereas the adjacent passage has very high momentum in the passage inlet and diffuses efficiently. Experimental measurements confirm the S-shape of the pressure rise characteristic even if the stability limit experimentally occurs at higher mass flow than numerically predicted. At low mass flow the alternate stall pattern is confirmed thanks to the data obtained by high-frequency pressure sensors. As the compressor is throttled the path to instability has been registered and a f＇wst scenario of the surge inception is given. The compressor first experiences a steady alternate stall in the dif- fuser. As the mass flow decreases, the alternate stall amplifies and triggers the mild surge in the vaned diffuser. An unsteady behavior results from the interaction of the alternate stall and the mild surge. Finally, when the pres- sure gradient becomes too strong, the alternate stall blows away and the compressor enters into deep surge.展开更多
The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence...The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence of flow instability such as stall and surge. The paper experimentally examines the developing process of surge and stall occurring in a centrifugal compressor to advance the understanding on flow mechanism of flow instability. It is found that three types of pressure fluctuation can be observed at low flowrate region. At the critical point, the local stall firstly occurs in some specific diffuser passages and the enlarged local diffuser stall eventually induces the mild surge of compression system indicated by the sinusoidal pressure fluctuation. At lower mass flow rate, the diffuser stall cell begins to circumferentially propagate along the impeller rotating direction at 11% of rotor speed with the existence of mild surge. In comparative analysis of IGV pre-swirl angle on the occurrence of mild surge, the mild surge still occurs at the operating condition when the slope of the characteristic map of test stage is still obviously negative, in which the compression system is supposed to be stable in previous study. And a new suggested criterion for the prediction of mild surge is demonstrated that the occurrence of mild surge depends on the destabilization effect of downstream components about diffuser and volute. Combined with the experimental data, the streamwise distribution characteristic of diffuser stall can be used to develop the simplified model of lumped parameters for the analysis on the generation mechanism of the diffuser rotating stall. The quantitative investigation on the relation between the pressure-rise characteristic of subcomponents and the occurrence of mild surge and diffuser rotating stall not only advances the prediction of stability limit but also lays the theoretic foundation for controlling these unsteady behaviors to improve the operating range.展开更多
基金funding from the European Union Seventh Framework Program(FP7)through the ENOVAL project under grant agreement n°604999
文摘The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines. The compressor is composed of inlet guide vanes, a backswept splittered un- shrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes. Previous numerical simulations revealed a particular S-shape pressure rise characteristic at partial rotation speed and predicted an alternate flow pattern in the vaned radial diffuser at low mass flow rate. This alternate flow pattern involves two adjacent vane passages. One passage exhibits very low momentum and a low pressure recovery, whereas the adjacent passage has very high momentum in the passage inlet and diffuses efficiently. Experimental measurements confirm the S-shape of the pressure rise characteristic even if the stability limit experimentally occurs at higher mass flow than numerically predicted. At low mass flow the alternate stall pattern is confirmed thanks to the data obtained by high-frequency pressure sensors. As the compressor is throttled the path to instability has been registered and a f＇wst scenario of the surge inception is given. The compressor first experiences a steady alternate stall in the dif- fuser. As the mass flow decreases, the alternate stall amplifies and triggers the mild surge in the vaned diffuser. An unsteady behavior results from the interaction of the alternate stall and the mild surge. Finally, when the pres- sure gradient becomes too strong, the alternate stall blows away and the compressor enters into deep surge.
基金supported by the National Key R&D Program of China(Grant No. 2018YFB0606102)National Science&Technology Major Project (Grant No. 2017-II-0004-0016)National Natural Science Foundation of China (Grant No. 51790512)。
文摘The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence of flow instability such as stall and surge. The paper experimentally examines the developing process of surge and stall occurring in a centrifugal compressor to advance the understanding on flow mechanism of flow instability. It is found that three types of pressure fluctuation can be observed at low flowrate region. At the critical point, the local stall firstly occurs in some specific diffuser passages and the enlarged local diffuser stall eventually induces the mild surge of compression system indicated by the sinusoidal pressure fluctuation. At lower mass flow rate, the diffuser stall cell begins to circumferentially propagate along the impeller rotating direction at 11% of rotor speed with the existence of mild surge. In comparative analysis of IGV pre-swirl angle on the occurrence of mild surge, the mild surge still occurs at the operating condition when the slope of the characteristic map of test stage is still obviously negative, in which the compression system is supposed to be stable in previous study. And a new suggested criterion for the prediction of mild surge is demonstrated that the occurrence of mild surge depends on the destabilization effect of downstream components about diffuser and volute. Combined with the experimental data, the streamwise distribution characteristic of diffuser stall can be used to develop the simplified model of lumped parameters for the analysis on the generation mechanism of the diffuser rotating stall. The quantitative investigation on the relation between the pressure-rise characteristic of subcomponents and the occurrence of mild surge and diffuser rotating stall not only advances the prediction of stability limit but also lays the theoretic foundation for controlling these unsteady behaviors to improve the operating range.
