| With the increasing demand for space transportation,the requirements for high-speed aircraft are also increasing,which promotes the research of combined-cycle power system by scholars in the industry.The turbine-based-combined-cycle engine(TBCC),which combines turbine engine and ramjet,has the advantages of wide flight range,high specific impulse in each flight range,horizontal take-off and landing,reusable and so on.As the inlet part of TBCC engine,the two-dimensional external over/under TBCC inlet studied in this paper mainly undertakes the flow distribution of ram channel and turbine channel and the switching of two channels in the process of mode transition.In addition,for the two-dimensional external over/under TBCC inlet,the two channels are independent of each other,and also have the advantages of small interference,easy design of adjustment mechanism and relatively simple adjustment scheme.In this paper,the transient numerical simulation of the mode transition of the two-dimensional external over/under TBCC inlet is carried out,and the starting characteristics and performance changes of the inlet during the mode transition are studied.Firstly,the corresponding experimental model is designed,and the design process is introduced and summarized.Secondly,under the condition of incoming flow Ma3,through steady numerical simulation,explore the incoming flow attack angle when the ram channel was not started by the splitter fully closed,and then carried out transient numerical simulation on the forward and reverse mode transition of TBCC inlet in the range of unstart incoming flow attack angle,so as to study the starting characteristics of ram channel under the condition of large attack angle.The results show that when the angle of attack is greater than 4 °,the ram channel will not start in the forward mode transition,and the ram channel can be restarted in the process of reverse mode transition,and there is hysteresis in the unstart / restart of ram channel in this process;The parameters at the outlet of the ram channel form a hysteresis loop;The reason for the hysteresis is that the ICR of the stamping channel passes through the isentropic limit and Kantrowitz limit,and their values are inconsistent.Thirdly,the starting characteristics of the stamping channel was studied,when different back pressure was applied to the stamping channel and fixed back pressure was applied.Then applied the back pressure to the turbine channel to carry out mode transition,the starting characteristics of the turbine channel and its influence to the ram channel were studied respectively.The results show that the unstart / restart boundary of ram channel caused by back pressure is basically consistent with the boundary obtained by changing the position of splitter plate,and the double solution region of back pressure is larger than that of splitter plate.The back pressure will reduce the outlet Mach number and total pressure recovery coefficient of the inlet,but the outlet mass flow coefficient will not decrease before the inlet is unstarts,and the ram channel will not be affected before the turbine channel unstarts.When the turbine channel is not started,the ram channel will unstart immediately.Finally,the transient numerical simulation of the coupling motion of the splitter plate and the crow plate was carried out,and the starting characteristics of the ram channel at different speeds and starting times of the crow plate were studied.The results show that when the rotating speed of the splitter plate is fixed,the faster the rotating speed of the crow plate,the more forward the starting time of rotation,and the less easy it is for the stamping channel unstart in the process of modal transition.The more forward the splitter plate is,the bigger the ICR si,when the ram channel does not start.By adjusting the crow plate motion scheme,the outlet performance of the ram channel can be as higher as possible. |
