Design and performance analysis of an exhaust system for an over-under turbine based combined cycle operating at Mach 0–6

Abstract

The present study focuses on the design and performance analysis of an exhaust system for an over-under turbine based combined cycle (TBCC) operating at Mach 0–6. The computational fluid dynamics (CFD) approach is employed to obtain the flowfield and performance of the exhaust system. The single expansion ramp nozzle (SERN) considering geometric constraints at the cruise condition is designed by a new method based on maximum thrust theory, and the initial expansion angle on the cowl is set at 0.37 rad. The lower cowl is sliding as well as rotating around a fixed point to satisfy the adjustment requirement of the high-speed flowpath, and shifting the location of the fixed point forward has a positive effect on the performance of the exhaust system. In order to eliminate the adjustment interaction between the low-speed and high-speed flowpaths and decreases the expansion ratio of the low-speed flowpath, the splitter location is shifted backward, and the optimal location and top contour angle of the splitter are set to 220 mm and 20°, respectively. The flowfield structure is relatively simple at the separate operation, while it is obviously complex at the parallel operation, with the flow interaction between the turbine exhaust jet and rocket ejector plume. With the increase in the flight Mach number, the axial thrust coefficient is increased rapidly at the separate operation of the turbine, while it increases firstly and then decreases at the parallel operation. For the separate operation of the high-speed flowpath, the axial thrust coefficient maintains above 0.96 and also increases firstly and then decreases gradually as the increase in the flight Mach number.