Sem DE MAAG, Jan Siemen SMINK, Edwin T.A. VAN DER WEIDE, Harry W.M. HOEIJMAKERS, Cornelis H. VENNER
DOI Number: 10.60853/hrs7-f678
Conference number: HiSST-2024-00181
In order to minimize the length of supersonic-combustion ramjets (scramjets), injected fuel should mix rapidly with the supersonic cross flow. Tandem dual jet injection shows improved mixing performance over single jet injection. The present study comprises experimental work, using Schlieren flow visualisation in the supersonic wind tunnel of the University of Twente, as well as numerical simulation of the flow inside this wind tunnel, both at Mach number 1.6. The numerical simulation is based on (a) the Reynolds-averaged Navier Stokes (RaNS) equations for time-averaged flow for exploratory purposes; and (b) the time-resolved hybrid RaNS-LES, Delayed Detached Eddy Simulation (DDES) on a grid of
35M points. The Schlieren images from the experiments are analysed using a semi-automated post-processing procedure that generates an iso-incidence plot from which the time-averaged location of the upper boundary of the jet shear layer is determined. Subsequently an overall measure for the penetration depth of the main jet plume into the cross flow is found. The penetration depth is a function of two parameters (i) 𝐽, the ratio of the momentum of the jet and that of the cross flow and (ii) the nondimensionalized distance 𝑆 between the dual jets. Based on Schlieren images from 24 (S,J)-combinations, the experimental work resulted in an empirical (scaling) similarity relation for the time-aver-aged location of the upper boundary of the jet plume and for the penetration depth. The empirical relationship has been validated by results from experiments for a further 21 (S,J)-combinations. The
empirical relation shows that there is a region in the (S,J)-plane where the penetration depth is optimal:for given J there is an S for which the penetration is maximal. Numerical simulations facilitated the analysis of the time-dependent flow in great detail, using spatial distributions of vorticity, Mach number and total pressure. Furthermore, the spatial distribution of the density is used to generate numerical Schlieren images. These were run through the post-processing procedure for wind-tunnel Schlieren images. So far, DDES numerical simulations have been carried out for one representative (S,J)-combination. Its results were used to obtain insight in the flow phenomena that occur in the jet plume interacting with the cross flow. These results also validated the empirical similarity relation for the penetration depth of the jet plume.