Study On Aerodynamic Design Optimization And Flight Stability Of Hypersonic Waveriders

Hypersonic flight is undergoing the development from the traditional ballistic re-entry flight to the long-endurance manoeuvring flight in the near space.For the near-space long-range manoeuvring hypersonic vehicles,high lift-to-drag ratio is the basic requirement.For hypersonic waveriders,the shock wave is attached to the leading edge,thus preventing the spillage of high pressure gas from the lower surface onto the upper surface and achieving much better aerodynamic efficiency than other traditional hypersonic configurations,which makes the waverider a very promising and valuable configuration in the design of hypersonic vehicles.However,many problems remain to be studied and solved towards the real application of waverider to the actual hypersonic vehicles.The purpose of this paper is to study the aerodynamic optimization method and static/dynamic stability of hypersonic waveriders.The main work is arranged as follows:1)The influence of strong viscous interaction effects on the shock wave position and lift-to-drag ratio of the waverider is evaluated by CFD numerical simulation.It’s discovered that at the Mach number of the design condition,the shock wave position is deflected downwards evidently.Thus,the paper first proposes a vorticity-based method to obtain the boundary layer displacement thickness in combination with the tangent wedge/cone method.Then,trying to alleviate the high pressure gas leakage near the leading edge,a viscous optimized waverider is modified by deducting the boundary layer displacement thickness from the original lower surface along the normal direction.Results show that the shock wave position around the lower surface of the modified waverider under the condition of strong viscous interaction is very close to that of the inviscid basic flowfield around the original waverider.What’s more,due to the lower pressure near the leading edge of the modified lower surface,the wave drag is lowered for the same lift,thus the lift-to-drag ratio is improved.2)The problem of longitudinal stability limits the engineering application of the waverider configuration to some extent.To solve the problem,the paper proposes a design method of hypersonic quasi-waverider configuration.In the generation process,the leading edge of the original waverider is kept unchanged.Then at different longitudinal cross section,the profile of the lower surface is determined by the same curve equation,started from the point at the leading edge and cut off at the base plane.The profile function is determined by the sum of a series of power law functions,whose coefficients can be changed and optimized according to different design requirements.Different quasi-waveriders are obtained according to different constraints and the final aerodynamic characteristics are evaluated via CFD simulations.Results show that for this kind of configurations,good shock attachment near the leading edge can be achieved and the pressure distribution on the lower surface is uniform.Different quasi-waveriders with excellent aerodynamic efficiency can also be generated by different constraints of volume efficiency.Finally,a trim-constrained longitudinally static stable quasi-waverider is generated.However,when the leading edge is blunted,longitudinal instability is discovered at large angles of attack.For this problem,a cutting method is proposed to improve the longitudinal static stability.3)Lateral and directional stability is a key and difficult issue in the design of hypersonic waverider vehicles.Parametric study for the lateral and directional stability of the waverider is conducted.In combination with steady/unsteady CFD results and the Kriging surrogate model,the distribution of lateral and directional static stability with the leading edge design parameters is obtained.The distribution of lateral-directional coupled dynamic stability modes is also obtained according to the solution of linearized small-disturbance equations for lateral-directional motions.The reason for divergence of each mode is explained via the corresponding approximate expression by mode simplification.A concise and effective approximate expression is derived for the damping of the Dutch roll mode.And a new concept of the Dutch roll dynamic stability derivative N_pDYN is defined.Results show that N_pDYN plays a major role in the variation of Dutch roll damping.4)In order to rapidly evaluate the unsteady aerodynamic forces of hypersonic waveriders in the initial design process,two hypersonic unsteady aerodynamic models are developed in this paper.Firstly,the local piston theory with viscous correction（VLPT）is developed.Then the paper establishes an unsteady aerodynamic reduced order model based on system identification——the ARX model.The two models are applied to the calculation of the dynamic derivatives of hypersonic waveriders.Furthermore,in order to evaluate the lateral-directional coupled dynamic characteristics of hypersonic waveriders rapidly and efficiently in the initial design process,an ARX/RBD state space model is developed.The results from ARX/RBD are compared with those obtained from CFD/RBD numerical simulation,demonstrating the high accuracy and efficiency of the model.The efficiency can be even improved as high as one to two orders of magnitude.