Thrust loss analysis of a turbine-based combined cycle nozzle

In this study, a parallel turbine based combined cycle (TBCC) combined nozzle is designed and investigated. Two-dimensional computational fluid dynamics are conducted using the SST k-ω two-equation model. The basic single expansion ramp nozzle (SERN) contours at the design point are designed using a new method based on maximum thrust theory. The forces contributions from different SERN segments are statistically analyzed. Losses due to non-full and non-isentropic expansion are compared across different contours, with the cowl’s initial expansion angle set at 0.31 rad. The adjustment scheme of the combined nozzle includes a splitter to form the turbojet nozzle throat and a hydraulic cylinder to form the ramjet nozzle throat. According to the geometric relationship, the turbojet flow-path inlet height (H_i,tur) and the splitter length (L_spl) are selected as optimization parameters of this adjustment scheme. The influence of H_i,tur and L_spl on the performance trend for the same configuration under different working conditions, as well as the relative magnitude for different configurations under the same working condition are analyzed. Exit height constraint loss determines the upper limit of nozzle performance, while nozzle design loss and non-isentropic expansion loss determine the specific numerical value of nozzle performance. Analysis of geometric parameters influence on expansion process and estimation of different kinds of thrust losses can improve design efficiency, and enable nozzle performance prediction during geometric selection stage.