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
Full annulus simulations of the flow which develops in a transonic centrifugal compressor are performed at two stable operating points （peak efficiency and near surge） and during the path to surge. At stable conditi...Full annulus simulations of the flow which develops in a transonic centrifugal compressor are performed at two stable operating points （peak efficiency and near surge） and during the path to surge. At stable conditions, the flow field properties are analyzed by comparisons with experimental data and numerical simulations using a phase lagged approach previously carried out. Regarding the stage overall performance, an excellent agreement is obtained between the numerical results （both with time lagged approach and full-annulus calculation） and the ex- periments. From the full-annnlus simulations, the change in flow pattern from peak efficiency to surge is found to be perfectly similar to that obtained from the simulations using the time lagged approach. In particular, pro- vided that the operating point is stable, the flow proves to be chorochronic. The full-annulus simulations were continued after a unique small change in the throttle law applied at the exit of the numerical domain. The mass flow, pressure ratio and efficiency then significantly drop all the more the time progresses. The simulation becomes unstable and the surge inception well underway. The path to surge is found to be due to the enlargement of the boundary layer separation on the suction side of the diffuser vanes in accordance with the conclusions drawn from the chorochronic simulations and experiments. But as the time progresses, the flow loses its chorochronic character. Stall cells rotating at around 7% of the rotor speed develop and lead to surge in around 5 revolutions.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the HPC resources of CINES under the allocation 2012- 2a6356 and 2013-2a6356
文摘Full annulus simulations of the flow which develops in a transonic centrifugal compressor are performed at two stable operating points （peak efficiency and near surge） and during the path to surge. At stable conditions, the flow field properties are analyzed by comparisons with experimental data and numerical simulations using a phase lagged approach previously carried out. Regarding the stage overall performance, an excellent agreement is obtained between the numerical results （both with time lagged approach and full-annulus calculation） and the ex- periments. From the full-annnlus simulations, the change in flow pattern from peak efficiency to surge is found to be perfectly similar to that obtained from the simulations using the time lagged approach. In particular, pro- vided that the operating point is stable, the flow proves to be chorochronic. The full-annulus simulations were continued after a unique small change in the throttle law applied at the exit of the numerical domain. The mass flow, pressure ratio and efficiency then significantly drop all the more the time progresses. The simulation becomes unstable and the surge inception well underway. The path to surge is found to be due to the enlargement of the boundary layer separation on the suction side of the diffuser vanes in accordance with the conclusions drawn from the chorochronic simulations and experiments. But as the time progresses, the flow loses its chorochronic character. Stall cells rotating at around 7% of the rotor speed develop and lead to surge in around 5 revolutions.
