The effect of axial-flow swirling generator and drainage structure with diversion cone on separation performance is very important to supersonic separators. But there is in the absence of experimental studies on separation characteristics of above-mentioned structure. In this paper, both experimental and numerical methods are utilized to investigate the influences of swirling generator and drainage structure. Good agreements are achieved between experimental data and high-order numerical simulation. The results demonstrate that the rotation strength decreases as the outlet angle of the swirler increases. The rotational flow causes the inconsistency of the radial distribution of the fluid in the nozzle and the inconsistency is more noticeable with the increase of rotation intensity. So the blade angle of swirling generator should be determined to find the balance between the expansion characteristic and swirling flow. Comparing two types of drainage structures, the internal extension structure has seriously damaged the supersonic flow in the nozzle, while the flush type drainage port has less influence on fluid. And the smaller outlet angle of drainage port can reduce the effect of drainage port on supersonic flow. When the pressure ratio is 1.4 for the flush type drainage structure, the optimal structural parameter is that the outlet angle of swirler is 55 and the inclination of the drainage structure is 22. Under the optimum conditions, the ethanol removal rate is 57.06%. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.