Optimization of B-Spline Launch Vehicle Payload Fairing

Abstract

Payload fairing (PLF) provides protection for the payload carried by a launch vehicle from external flow and aerodynamic heating. Not only the PLF should be able to accommodate the required payload volume inside it, it should have desirable aerodynamic features like low drag, low transonic shock strength, low base bending moment, etc. The PLF shape design problem is posed as a multiobjective optimization problem with minimization of drag coefficient and maximization of PLF volume. A fairly general parameterization of the PLF shape has been constructed by using B-Splines. The shape parameters constitute the design variables. The control points of the B-Splines formed the design variables.The design space also included the Mach number in addition to the control point co-ordinates. The design space was sampled using Random Latin Hypercube Sampling (RLHS). For the study, 160 PLF designs were constructed and CFD simulations were carried out. CFD studies were carried out to evaluate the aerodynamics of these configurations. Validation studies were done for a particular configuration at various Mach numbers. An open-source mesh generation software, Gmsh, was used along with the open-source CFD solver, SU2, and the Paraview flow visualization software for postprocessing. Grid independence, domain independence, scheme independence, and turbulence model independence studies were performed for a reference geometry before getting into the detailed CFD simulations. Axisymmetric Reynolds Averaged Navier Stokes (RANS) CFD simulations were carried out using SST turbulence model. Second-order spatial discretization was employed and the ROE solver with Venkatakrishnan Limiter was used. An ANN surrogate model was constructed to estimate the drag coefficient as a function of the design variables. The optimization studies brought out that the conical configurations was optimal for lower volumes at supersonic Mach numbers, whereas blunt configuration was optimal for all cases of transonic regime for the objectives considered in the present study.