Simulation of supersonic forced transition by a multiport array injector

This paper reports the first high-fidelity numerical study of compressible turbulent transition behind a multiport injector array (MPIA). The flow considered is an axisymmetric supersonic inlet, recently tested experimentally at The University of Queensland, that used an MPIA to induce turbulent transition by injecting a small amount of pure Nitrogen into the boundary layer. A single row of four 0.2 mm porthole injectors is simulated using Detached Eddy Simulation (DES), at an experimental condition corresponding to Mach 7.6 flight at a dynamic pressure of 50 kPa. The simulations show that the MPIA injection results in large scale instabilities that immediately trip the boundary layer into a turbulent state. These instabilities have a dominant frequency superimposed on the turbulent wave structure, with a base wavelength of approximately 5 mm. The source of this regularity appears to be periodic oscillation of the final fuel jet, which in turn is dynamically coupled to the upstream jets in an complex and interesting manner which has not been described before. The turbulent flow behind the MPIA results in an increase in wall heat transfer that counteracts any film cooling that may be present from the injectors. The DES prediction of the heat transfer rates compares favourably to experimental measurements, and RANS simulations using the Spalart-Allmaras and Menter SST models are found to underpredict wall heat transfer throughout the domain. • Multiport injector arrays can be used as turbulent trips with low fluidic losses. • High fidelity numerical simulation is needed to resolve the resulting transition process. • Periodic jet interactions have been discovered between neighbouring injectors, with wavelengths in the millimetre range. • Detacted Eddy Simulation outperforms industry standard turbulence modelling at predicting wall heating behind the MPIA.