The temporal behaviour of a flow separation in the hub-suction side comer of a transonic diffuser is studied thanks to unsteady numerical simulations based on the phase-lagged approach. The validity of the numerical r...The temporal behaviour of a flow separation in the hub-suction side comer of a transonic diffuser is studied thanks to unsteady numerical simulations based on the phase-lagged approach. The validity of the numerical re- sults is confn＇med by comparison with experimental unsteady pressure measurements. An analysis of the instan- taneous skin-friction pattern and particles trajectories is presented. It highlights the topology of the separation and its temporal behaviour. The major result is that, despite of a highly time-dependent core flow, the separation is found to be a ＂fixed unsteady separation＂ characterized by a fixed location of the main saddle of the separation but an extent of the stall region modulated by the pressure waves induced by the impeller-diffuser interaction.展开更多
We report an unusual non-storm erosion event of outer zone MeV electron distribution during three successive solar wind number density enhancements(SWDEs)on November 27-30,2015.Loss of MeV electrons and energy-depende...We report an unusual non-storm erosion event of outer zone MeV electron distribution during three successive solar wind number density enhancements(SWDEs)on November 27-30,2015.Loss of MeV electrons and energy-dependent narrowing of electron pitch angle distributions(PAD)first developed at L^(*)=5.5 and then moved down to L^(*)<4.According to the evolution of the electron phase space density(PSD)profile,losses of electrons with small pitch angles at L^(*)>4 during SWDE1 are mainly due to outward radial diffusion.However during SWDE2&3,scattering loss due to EMIC waves is dominant at 4<L^(*)<5.As for electrons with large pitch angles,outward radial diffusion is the primary loss mechanism throughout all SWDEs which is consistent with the incursion of the Last Closed Drift Shell(LCDS).The inner edge of EMIC wave activity moved from L^(*)~5 to L^(*)~4 and from L~6.4 to L~4.2 from SWDE1 to SWDE2&3,respectively,observed by Van Allen Probes and by ground stations.This is consistent with the inward penetration of anisotropic energetic protons from L^(*)=4.5 to L^(*)=3.5,suggesting that the inward extension of EMIC waves may be driven by the inward injection of anisotropic energetic protons from the dense plasma sheet.展开更多
Aerodynamic test rigs are necessary for experimental testing of turbomachines and investigation of possible ways to improve machine performance.Existing instal-lations give higher losses and do not work efficiently at...Aerodynamic test rigs are necessary for experimental testing of turbomachines and investigation of possible ways to improve machine performance.Existing instal-lations give higher losses and do not work efficiently at off-design operating modes.An operating part with an adjustable radial diffuser was designed in order to deter-mine the characteristics of turbine annular cascades.Experimental studies and computational verifications showed satisfactory results at various operating modes.The regulated backwall of the radial diffuser ensured supersonic velocity values behind the cascade and overall stable operation in a wide range of Mach numbers up to 1.3 when using compressors of comparatively small capacity.The optimum positions of the regulated backwall were determined,which provided a deep vacuum behind the cascade,as well as 1.5 times Mach number increase compared to the turbine cascade without a diffuser.Changing the inlet channel geometry at supersonic modes leads to an increase in the diffuser efficiency.Additionally,it was determined that the use of the turbine vane cascade in the test rig flow path is not necessary during calculation studies,but instead an axisymmetric vaneless converging area can be applied and give satisfactory results as well as reduce the time spent on calculations.The computational model can be used to optimize the design of an aerodynamic tunnel outlet area.展开更多
文摘The temporal behaviour of a flow separation in the hub-suction side comer of a transonic diffuser is studied thanks to unsteady numerical simulations based on the phase-lagged approach. The validity of the numerical re- sults is confn＇med by comparison with experimental unsteady pressure measurements. An analysis of the instan- taneous skin-friction pattern and particles trajectories is presented. It highlights the topology of the separation and its temporal behaviour. The major result is that, despite of a highly time-dependent core flow, the separation is found to be a ＂fixed unsteady separation＂ characterized by a fixed location of the main saddle of the separation but an extent of the stall region modulated by the pressure waves induced by the impeller-diffuser interaction.
基金supported by NSFC grants 41474139,41731068,and 41674164the support from the China Postdoctoral Science Foundation through grant 2019 M650316。
文摘We report an unusual non-storm erosion event of outer zone MeV electron distribution during three successive solar wind number density enhancements(SWDEs)on November 27-30,2015.Loss of MeV electrons and energy-dependent narrowing of electron pitch angle distributions(PAD)first developed at L^(*)=5.5 and then moved down to L^(*)<4.According to the evolution of the electron phase space density(PSD)profile,losses of electrons with small pitch angles at L^(*)>4 during SWDE1 are mainly due to outward radial diffusion.However during SWDE2&3,scattering loss due to EMIC waves is dominant at 4<L^(*)<5.As for electrons with large pitch angles,outward radial diffusion is the primary loss mechanism throughout all SWDEs which is consistent with the incursion of the Last Closed Drift Shell(LCDS).The inner edge of EMIC wave activity moved from L^(*)~5 to L^(*)~4 and from L~6.4 to L~4.2 from SWDE1 to SWDE2&3,respectively,observed by Van Allen Probes and by ground stations.This is consistent with the inward penetration of anisotropic energetic protons from L^(*)=4.5 to L^(*)=3.5,suggesting that the inward extension of EMIC waves may be driven by the inward injection of anisotropic energetic protons from the dense plasma sheet.
文摘Aerodynamic test rigs are necessary for experimental testing of turbomachines and investigation of possible ways to improve machine performance.Existing instal-lations give higher losses and do not work efficiently at off-design operating modes.An operating part with an adjustable radial diffuser was designed in order to deter-mine the characteristics of turbine annular cascades.Experimental studies and computational verifications showed satisfactory results at various operating modes.The regulated backwall of the radial diffuser ensured supersonic velocity values behind the cascade and overall stable operation in a wide range of Mach numbers up to 1.3 when using compressors of comparatively small capacity.The optimum positions of the regulated backwall were determined,which provided a deep vacuum behind the cascade,as well as 1.5 times Mach number increase compared to the turbine cascade without a diffuser.Changing the inlet channel geometry at supersonic modes leads to an increase in the diffuser efficiency.Additionally,it was determined that the use of the turbine vane cascade in the test rig flow path is not necessary during calculation studies,but instead an axisymmetric vaneless converging area can be applied and give satisfactory results as well as reduce the time spent on calculations.The computational model can be used to optimize the design of an aerodynamic tunnel outlet area.
