Aerospike: an hybrid parametric-adjoint approach for the optimal design

One of the characteristics of an hypersonic vehicle (in particular for missiles, rockets, and re-entry vehicles) is that the front part of the fuselage has the shape of a blunt body: this architecture is mandatory to allow the presence of a reasonable inner space to store the payload, the electronics and eventually the crew, which also helps to decrease speed during re-entry.The presence of this dome-shaped part induces, for instance, i) an increase of the pressure load onto the body, ii) ablation of hull covering materials, iii) mechanical failures, iv) heat damage to the onboard electronic packages, and v) communication failure due to air ionization ahead of the vehicle. Those effects are related to the shock wave onset near the dome that induces large drag and temperature increase in the near-body region.The installation of a static device called aerospike at the stagnation point generates a recirculating zone backward that creates a virtual streamlined body due to the separated zone that acts like a "fluid wall" reducing the strength of the normal shock wave.This strongly depends on the geometric characteristic of the aerospike (head shape and radius, aerodisk length). The aim of this work is the definition of an optimal design using different techniques (parametric optimization, adjoint optimization) considering the impact of that characteristic on the drag and the temperature load induced on the dome-shaped forebody.The parametric approach is used to study the effect of the aerospike length, the aerodisk radius and to test different head shapes while the result of the last one is used as the input for the head shape optimization using the adjoint approach;the head used as the baseline for the adjoint optimization is, in fact, the spherical one, which has one of the best performances in terms of drag reduction and thermal protection.The adjoint-shaped heads improved upon the best "standard head" by ≃ 5 % , leading to an overall drag coefficient reduction of the 59.3 %