Supersonic Boundary-Layer Combustion via Multiporthole Injector Arrays

The flowfield characteristics of boundary-layer combustion using a multiporthole injector array were investigated in a numerical study. Hydrogen fuel was injected at four different mass flow rates and two streamwise porthole spacings within the boundary layer on a flat plate through an array of small portholes in a Mach 4.5 crossflow. The jet-to-jet spacings used were those identified in a previous investigation of film cooling as yielding the greatest drag reduction and mixing efficiency, respectively. The effect of injectant mass flow rate and streamwise jet-to-jet spacing was investigated using the three-dimensional Reynolds-averaged Navier-Stokes equations with Menter's shear stress transport turbulence model and a 13-species, 33-reaction hydrogen-air chemistry model. At high injection mass flow rates, ignition occurred at the injection point; however, the ignition length increased as the mass flow rate was decreased. At the lowest injection rate, ignition did not occur within the investigated domain. Where combustion occurred, significant thickening of the boundary layer and high local heating was found near the ignition point. Total viscous drag reductions of up to 78% over a plate length of 0.5m were achieved. The mechanism of drag reduction was found to be associated with a reduction in near-wall Reynolds stresses. Even with the presence of combustion in the boundary layer, significant wall heat transfer rate reductions were also found in all cases compared with no injection.