The three dimensional Reynolds-averaged N-S equations and the standard k-ε turbulent model were adopted to simulate numerically the flow field of the three-dimensional flow-path of the supersonic expander under three kinds of strake wall section shapes at the design point. It's found that the suction surface of supersonic expander with rectangle strake wall section shape has high air velocity

low flow losses after the shock waves

and thus higher adiabatic isentropic efficiency can be obtained; the supersonic expander with positive trapezoid strake wall section shape has high outlet averaged Mach number

static pressure ratio and expansion ratio

its comprehensive performance is relatively optimal; the main sources of flow losses at outlet include low-speed air caused by corner boundary layer separation and backflow as well as pressurization process of high-speed air after oblique shock waves. The comprehensive performance of supersonic expander could be further enhanced by optimizing the structure of strake wall in radial direction.