Abstract: To examine the influences of some typical design parameters(the inlet flow condition,blade number,and vane loading distribution) on the performances of the return vanes in a two-stage centrifugal compressor,a series of return vanes were designed and analyzed numerically by 3-D viscous code.It was found that the secondary flows in the return vane were usually very strong;however,improving the inlet flow uniformity,increasing the blade number and optimizing the vane loading distribution could weaken the secondary flows.Among these approaches,the effect of changing the vane loading distribution was most significant.Generally,the forward loading return vane could achieve higher total pressure recovery coefficient and much more uniform discharge flow than the backward loading return vane.