The Experimental and Numerical Study of the Over-Under TBCC Exhaust System

Based on the previous research on the design method and numerical simulation of an over/under turbine based combined cycle(TBCC) exhaust system, which was consisted of a turbojet exhaust nozzle and ramjet exhaust nozzle, the experimental study was further conducted to evaluate the performance of TBCC exhaust nozzle. The main objectives of the study were as followings: (1) To identify any interactions between the two exhaust jet streams dur ing the mode transition phase and its effect on the whole flowfield structure; (2) To determine and v erify the aerodynamic performance of the over/under TBCC exhaust nozzle; (3) To validate the simula tion ability of the CFD Software according to the experiment condition. Test was conducted using a 9 percent scale model representing a single module of a TBCC exhaust nozzle. The static pressure taps and Schlieren apparatus were employed to obtain the wall pressure distributions and fl owfield structures. Steady-state tests were performed with the ramjet nozzle cowl at six different positio ns, at which the turbine flowpath were half closed and fully opened respectively. To fully understand the flow of the TBCC exhaust system during the mode transition, methods of computational fluid dynamics were applied to simulate the aerodynamics within the turbine flowpath and ramjet flowpath under the same test conditions. Results indicated that the flow structure was complicated because the two exh aust jet streams interacted with each other during the exhaust system mode transition. The exhau st system thrust ratio varied from 0.9288 to 0.9657 during the exhaust system mode transit ion. From the comparison of experimental data and simulation results, it was shown that the simulat ions compared well with the test data, CFD method was proved an affective way to evaluate the aerodynamic perf ormance of the TBCC exhaust system during the exhaust system mode transition.