关键词: 二次流；流向涡；边界层；小扰动分析；进气道

Abstract: In order to investigate the mechanics of the formation of the secondary flows induced by the isentropic sidewall compression in the supersonic flat-plate boundary layers，a simplified flow model was proposed. Based on the small perturbation approach and numerical study，the nonuniformity of Mach number distribution of the inflow was investigated to illustrate its importance for the formation of the secondary flows. The results show that，the secondary flows induced by the sidewall compression are the characteristics of the mean flow-field and independent of the instantaneous interaction between the disturbances and the vortexes. Due to the different characteristics of propagation of compression waves in the main stream and the boundary layer，the flows are compressed non-uniformly by the sidewall，resulting in the cross-movement of the fluid in the boundary layer compared to that in the mainstream. The distinction of direction between density gradient and pressure gradient or barocliny is one of the important factors leading to the formation and development of the streamwise vortex.

Key words: Secondary-flow；Streamwise vortex；Boundary layer；Small perturbation approach；Inlet