Research On Design Method And Flow Characteristics Of TBCC Exhaust System

With the increasing requirement of long-range and high speed flight vechile, the research on scramjet engines and the future reusable combined cycle engines(e.g. Turbine Based Combined Cycle, TBCC) has become a global focus. An effective propulsion system is one of the key technologies for hypersonic vehicles, and the single expansion ramp nozzle(SERN) is an essential component of the propulsion system.In this paper, the design methods and flow characteristics for the two dimensional SERN with realistic inflow condition, the three dimensional SERN which highly integrated into the aircraft and the over/under TBCC exhaust system were studied by using a combination of theoretical analysis, numerical simulation and experimental method.Firstly, a method of characteristics computer program has been developed for designing asymmetric scramjet nozzles, including the effects of nozzle nonuniform inflow and the influences of nonuniform inflow profiles of Mach number, temperature and pressures on the nozzle designing was investigated. The results indicate that the Mach number inflow profile has a most influence on the design results. Compared with the nozzle design with uniform inflow, the improvement of axial thrust coefficient in the nozzle design with nonuniform inflow is approximately 1 % at the design point. Moreover, the benefits on lift coefficient of the nozzle design with non-uniform inflow is approximately 6% at the design point, and the improvement of the pitching moment coefficient is also notable.Secondly, for the nonequilibrium flow in the nozzle at high Mach number, a method of characteristics computer program including the effects of finite-rate chemical reaction has been developed for designing scramjet nozzle. And numerical studies was performed to investigate the performance of scramjet nozzle designed by using method of characteristics including chemical nonequilibrium effects for a Mach 10 flight condition. Then it was compared with the nozzle which was designed with frozen flow assumption. The performance increment obtained by this method was about 3.2% for thrust and 3.6% for lift.Thirdly, a quasi-two-dimensional method of characteristics has been developed to design the three dimensional nozzle with lateral expansion. The design approach has been validated against the results of optimization design with high-fidelity computational fluid dynamics. The results show that the differences in axial forces for the quasi-two dimensional method of characteristics design and optimization design are quite low(less than 1%), and the differences in lift are not beyond 5% for the nozzle with lateral expansion contours. However, the computational time of this nozzle design could reduced from a few days to a few minutes by using this design approach.Finally, a novel method for optimizing the three dimensional section controllable scramjet nozzle is proposed. To generate the shape of the nozzle, the streamline tracing technique is utilized based on an annular optimum thrust nozzle flowfield calculated using the method of characteristics. In comparison with a conventional thrust optimized model, the proposed nozzle designed by streamline tracing technique obtains an increase of thrust by 1.0%, lift by 92.5% and the pitching moment by 19.7% under the same condition.Based on the above design results of the asymmetric nozzles, the design method of over/under TBCC exhaust system was investigated, and the optimization analysis on the arrangement between the turbine nozzle and the ramjet nozzle and the designing point of the TBCC exhaust system was conducted. The results showed that there is a optimal arrangement between the turbine nozzle and ramjet nozzle. During the whole flight corridor, the exhaust system performance were relatively poor at the transonic zone, and reducing the design point of the exhaust system is a effective way for improving the thrust performance at transonic.Further, cold flow tests on TBCC exhaust system at the low nozzle pressure ratios and during the transition mode are conducted, the flow characteristics and the pressure distributions of the nozzle are obtained, and the accuracy of the numerical methods are validated.