Research On Boundary-layer Flow Control For Hypersonic Inlet

The resistance to backpressure of hypersonic inlet has significant research value in engineering applications because it is closely related to both the performances of scramjet engine and whether the hypersonic vehicles can accomplish successfully the task using the scramjet as a propulsion power unit or not.Due to the bottleneck of finite compression for fixed geometry and the danger of unstart induced by combustion heat release,the mechanism of resistance to backpressure is explored based on theoretical analysis and numerical simulation,which provides technical reserves for stable and wide range of operation of hypersonic inlet,and which has reference value for real engineering applications.The backpressure propagation mode is firstly investigated.The typical unstart process of backpressure propagation is summarized.To provide control basis and standpoint for subsequently carrying out research on the resistance to backpressure of flow control,the backpressure propagation and balance property are analyzed.Simultaneously,the effects of wall temperature and skin friction on the balance property are also verified.Secondly,based on balance property of backpressure propagation,the mechanism of raised resistance to backpressure using boundary-layer suction and ejection is explored.The flow-control approach with increasing critical backpressure is discussed and the influences of suction and ejection on flow structure of shock-wave/boundary-layer interaction are mastered.The mechanism of local resistance to backpressure is given through local transformation of shock-wave system and local evolution of flowfield within suction slot.The critical iconic feature of local resistance to backpressure is proposed to represent the suction efficiency limitation.An empirical pressure rise expression is fitted by considering local pressure jump and quadratic distribution to analyze quantitatively the mechanism of local resistance to backpressure.Quantitative result with suction control indicates that the maximum backpressure tolerated by the inlet is increased approximate 12% with a loss of 1.88% of the mass flow rate of the mainstream.The flowfield characteristic with different ejection fluids is compared to reveal the differences of shock/boundary-layer interaction and the propagation path of backpressure as well as the mechanism of resistance to backpressure.The potential characteristic of the ejection total pressure which increases indirectly the ejection momentum and decreases the dynamic viscosity of ejection fluids is given,which promotes the mixing of momentum,mass and energy,thereby narrowing the subsonic band,suppressing the backpressure propagation.Especially for the cracking gas ejection control at the ejection total pressure of 4 MPa,the inlet's resistance to backpressure is increased by 11.76% with the utilization of ejection mass about 7.66% mass flow rate of mainstream.Then,the boundary-layer suction control for three-dimensional corner effect is studied.The influence of corner effect is concluded and the effect of corner effect on isolator's resistance to backpressure is compared and analyzed when the spanwise constraint is resolved.The influencing factors for postion of corner separation vortex and the formation of vortex structure of different cross sections in the pseudo-shock wave are further illustrated,thereby exploring the mechanisms of corner separation and resistance to backpressure as well as effective suction position.Lastly,due to additional mass flow loss for suction and additional energy based on turbo-pump supply of fuel of regeneratively cooled engine for ejection,the input-output efficiency assessment for both is investigated.The sensitivity of suction slot to backpressure and the selection principle for suction angle,position,and pressure ratio are analyzed.The dynamic mass flow loss and building process of suction are given in the process of the sharp opening of slot.A flow-control method of boundary-layer ejection is proposed based on the potential thermodynamic process in a turbo-pump supply system of fuel vapor within a cooling channel.The thermodynamic analysis,one-dimensional averaging method,and stream thrust analysis are used to reveal that the cycle pressure ratio is a crucial factor on high-quality energy utilization in the thermodynamic cycle.Increasing critical backpressure increases the compression capacity and efficiency,thereby increasing the specific thrust,specific impulse,and total efficiency.