Multi-Objective Design Optimisation of Inlet and Combustor for Axisymmetric Scramjets

Abstract

Hypersonic airbreathing propulsion, particularly scramjet propulsion, is a promising technology for efficient and economical access-to-space and high-speed atmospheric cruise. Compression of incoming flow in the inlet and combustion of fuel in the combustor play a major role in scramjet mechanism, their efficiencies having crucial influence on the overall scramjet performance. This paper presents the results of double-objective shape optimisation of the axisymmetric inlet and combustor configuration for minimum total pressure loss and maximum combustion efficiency. A state-of-the-art MDO (multi-objective design optimisation) capability with surrogate-assisted evolutionary algorithms has been employed, coupled with a CFD code, which solves the Euler equations including Evans & Schexnayder’s 12-species model for inviscid flowfields involving chemical reactions. Possibilities of substantial improvement in efficiency are suggested by the obtained Pareto optimal front, which indicates the counteracting nature of the two objective functions. Geometries with higher combustion efficiency, which incur greater total pressure loss, are characterised by a higher compression inlet with larger leading-edge nose-tip radius and a longer combustor. Opposite trends are observed for configurations with smaller total pressure loss yet lower combustion efficiency. The influence of these key design variables has been investigated by examining flowfields for the two extreme cases and baseline geometry.