Aerodynamic Shape Optimization of Payload Fairing Boat Tail for Various Diameter Ratios

Abstract

Aerodynamic shape optimization of launch vehicle hammerhead payload fairing (PLF) boat tail shapes has been carried out. Multi-objective optimization studies have been carried out to minimize the boat tail length, drag coefficient, the length of separated flow behind the boat tail, and the maximum pressure ratio over the boat tail. The boat tail shape has been parameterized using a B-spline. A novel optimal shape has been obtained, which has a shallow initial slope followed by a rapid increase in the slope near the boat tail end, termed the ramp stepped boat tail (RSBT). The optimization study has been carried out by varying the stage-to-PLF diameter ratios. A novel parameterization strategy has been employed, which convexifies the design space. Computational fluid dynamics (CFD) simulations have been carried out on 950 different boat tail configurations sampled using Latin hypercube sampling (LHS) at Mach number 0.8. Results from CFD have been validated against experimental data from literature. Artificial neural networks have been used as surrogate models for computing the objectives. Multi-objective optimization was carried out using the genetic algorithm for various stage-to-PLF diameter ratios. Pareto-optimal fronts obtained have been analyzed, and optimal shapes derived from them have been validated using CFD. It is found that the optimal RSBT configuration is found to be advantageous over the conventional conical boat tail in reducing drag, separated flow length, boat tail length, shock strength, and the turbulent kinetic energy downstream of the boat tail.