Multi-objective design optimization of precoolers for hypersonic airbreathing propulsion

A precooling heat exchanger has been the key mechanism for realizing turbine-based combined-cycle engines at high flight Mach numbers. A multi-objective design optimization coupling surrogate-assisted evolutionary algorithms with numerical simulation has been carried out with respect to three design objectives, that is, maximization of heat transfer effectiveness, total pressure recovery, and compactness. Physical insights into the underlying compressible aerodynamic and aerothermal phenomena in the bare tube bank geometry have been gained through scrutinizing the flowfields for the representative cases. With the nature of operating conditions having relatively high inflow velocity, tube bank configurations that are potentially prone to have flow choking are removed in the optimization process. The results from the optimization have been investigated by analyzing the selected individuals on the Pareto-optimal front and performing sensitivity analysis with the aid of surrogate models. The effects of uncertainties in the design parameters on the precooler performance have been examined. The unconventional tube profiles comprising elliptic and obround sections are found to effectively reduce unfavorable flow separation and permit smaller tube spacing ratios, yielding higher heat transfer rate per unit volume than the conventional circular tube bank.