This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based...This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing treatment configuration reveal an important modification of the vortex topology at the rotor tip clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is proposed.展开更多
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
This paper presents the unsteady data acquisition system used to measure the pressure field in high speed compressors.Details and electronic sketches are given for the conditioners developed in-house that have been us...This paper presents the unsteady data acquisition system used to measure the pressure field in high speed compressors.Details and electronic sketches are given for the conditioners developed in-house that have been used to amplify and to filter the pressure signal with the aim of acquiring data up to 150 kHz.A discussion of the experimental results carried out in a centrifugal compressor is proposed.Through different processing of the pressure signals and a comparison with URANS simulations,the excitation of the pressure transducers by the pressure waves generated by shock waves that occur between the impeller and the diffuser is highlighted.The levels of pressure fluctuations measured when entering into surge are also presented and reveal very repetitive behaviour of the flow instabilities.展开更多
文摘This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing treatment configuration reveal an important modification of the vortex topology at the rotor tip clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is proposed.
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 company Turbomeca which supports the centrifugal compressor research program
文摘This paper presents the unsteady data acquisition system used to measure the pressure field in high speed compressors.Details and electronic sketches are given for the conditioners developed in-house that have been used to amplify and to filter the pressure signal with the aim of acquiring data up to 150 kHz.A discussion of the experimental results carried out in a centrifugal compressor is proposed.Through different processing of the pressure signals and a comparison with URANS simulations,the excitation of the pressure transducers by the pressure waves generated by shock waves that occur between the impeller and the diffuser is highlighted.The levels of pressure fluctuations measured when entering into surge are also presented and reveal very repetitive behaviour of the flow instabilities.
