LES of the HyShot scramjet combustor

With the overall goal to clarify the physics of compressible (supersonic) combustion, a 3D LES of the HyShot supersonic combustor has been performed and is reported in this paper. HyShot is an (originally) Australian program to assess feasibility of supersonic combustion by means of a ballistic test flight. The HyShot combustion chamber is shaped as a box 75×9.8 mm in cross section and 300 mm long. Hydrogen is injected at 90 degrees with respect to the supersonic airstream 40 mm downstream from the combustor inlet by means of four 2 mm diameter choked orifices. Air enters the channel at a Mach number that, in the actual test, depended on the flight trajectory; in this simulation, the trajectory point is that at height = 28 km, where the Mach number was 2.79, P=82.11 kPa and T = 1229 K. A structured grid of about 14×106 nodes discretizes the actual combustor shape, where hydrogen-air combustion is treated by means of a detailed chemical kinetics model including 9 species and 37 reactions. Numerical results indicate that hydrogen penetrates in the air stream generating 3D bow shock structures upstream of the injection orifices as seen in experiments. In these regions recirculation zones upstream and downstream of the fuel injection orifices are observed as expected; the OH predicted by LES indicates that a flame starts already in the upstream recirculation zone. Interactions among the essentially 1D airstream entering the combustor, the heat released and the 3D jets produce large vorticity rates and therefore enhance and accelerate turbulent mixing. Combustion is predicted very fast and efficient: only 0.5% of hydrogen is found unburned at the combustor exit. Copyright © 2010 by A. Ingenito and C. Bruno