Expansion tube nozzle design using a parallel simplex algorithm

A new hypersonic Mach 12 nozzle has been designed and manufactured for a large-scale expansion tube. The nozzle design goals were to produce a Mach 12 flow, with a core flow diameter of at least 300 mm and a maximum exit flow angle non-uniformity of less than $${2}^{\circ }$$. The nozzle has been designed by coupling a RANS CFD solver with a parallel simplex algorithm to solve the computationally expensive optimisation problem. Novel aspects of this analysis are that it addresses nozzle optimisation specifically for scramjet test flows, characterised by high pressures and thick boundary layers. A new MPI implementation of a block-marching technique is used to solve the flowfield, which is optimised with a parallel Nelder–Mead algorithm. The validity of the objective functions is discussed through a robust bootstrapping analysis, and off-design performance of the nozzle is also characterised. The analysis demonstrates that the optimised contour achieves the design objectives and has excellent off-design performance. Initial commissioning experiments confirmed the results of the numerical analysis. Despite the final operating conditions being slightly off-design, the nozzle was able to produce an experimental core flow exceeding the numerical predictions. Indeed, the manufactured nozzle, 2.8 m long, with an exit diameter of 573 mm, has been shown experimentally to produce a core flow size of 360 mm, enabling full-scale Mach 12 scramjet experiments.