Hypersonic Cruise Vehicle Overall Parameters Analysis And Trajectory Optimization

Aiming at the maximum range of the cruise phase of hypersonic cruise vehicle,this thesis tries to answer the question from two aspects.On the one hand,from the perspective of aircraft design,the optimal steady-state cruise Mach number and altitude are adjusted to the predetermined position by optimizing aircraft parameters,so that the aircraft can perform cruise task with the minimum fuel consumption;On the other hand,for the finalized aircraft,the cruise trajectory is optimized,new methods for cruise trajectory optimization are developed,and the fuel consumption characteristics of the optimal trajectory and the mechanism of reducing fuel consumption are analyzed.Firstly,the influence of different aircraft parameters on the optimal cruise point is analyzed,and the aircraft parameter optimization method to adjust the optimal cruise point to the predetermined position is studied.There is an optimal cruise point with the minimum fuel consumption during steady-state cruise of hypersonic vehicle,and the position of the optimal cruise point is closely related to the aircraft parameters.It is found that the optimal cruise Mach number has a positive correlation with the inlet area and specific impulse,and a negative correlation with the drag coefficient and reference area,while the lift coefficient and aircraft mass have little effect on the optimal cruise Mach number;The optimal cruise altitude has a positive correlation with lift coefficient,inlet area,specific impulse and reference area,and a negative correlation with drag coefficient and aircraft mass.In order to accurately describe the influence of aircraft parameters on the optimal cruise point,a proxy model between aircraft parameters and the optimal cruise point is established by using a neural network with accuracy verified.Based on the model,a method of adjusting the optimal cruise point to the predetermined position by optimizing the aircraft parameters under multiple constraints is explored.The optimization result reveals how to adjust the aircraft parameters,which can provide guidance for the overall design of the aircraft.Secondly,on the basis of periodic cruise trajectory optimization,the cruise trajectory is studied under a constant equivalence ratio when engine is working.An improved particle swarm optimization algorithm is used to solve the trajectory optimization problem.The results show that for an aircraft whose specific impulse decreases with the increase of equivalence ratio,the fuel saving effect of cruise trajectory is better when the constant equivalence ratio is small,and the engine is working all the time,which is different from the switching change of the engine in traditional hypersonic periodic cruise.At the same time,maintaining a smaller equivalence ratio than that in steady-state cruise can also realize periodic cruise,and the fuel consumption is smaller than that in steady-state cruise.The fuel saving mechanism of the optimal trajectory is analyzed.It is found that the optimal trajectory has no obvious advantages in enhancing lift-drag ratio and reducing resistance work power.The main reason for saving a certain proportion of fuel is that the small equivalence ratio makes the engine obtain a larger specific impulse,and increasing the specific impulse and increasing the lift drag ratio are two aspects of mutual restriction.The optimal cruise trajectory is a balanced result of the two aspects.Finally,a new cruise trajectory optimization method whose equivalence ratio changes when engine is working is studied.In order to enhance the freedom of cruise trajectory and improve the efficiency of trajectory optimization algorithm,combined Downhill Simplex Method with Pseudo Spectrum Method,a hierarchical optimization process of cruise trajectory is developed.The angle of attack and equivalence ratio are dealt separately,and a result of larger fuel saving ratio is obtained.The analysis shows that the cruise trajectory with a changed equivalence ratio maintains the advantage of specific impulse,and further improves the lift drag ratio and reduces the resistance working power.Therefore,the optimization result has a better fuel consumption characteristics compared with the steady-state cruise trajectory.