Effects of flow disturbances from cross-stream fuel injection on the drag reduction by boundary layer combustion

A key issue that can aect the implementation of boundary layer combustion for viscous drag reduction in scramjet combustors is the potential of ow disturbances entering the combustor from the inlet. A source of ow disturbances comes from the cross-stream injection of fuel upstream of the combustor. Experiments were conducted in the T4 Stalker tube to study the eects of these ow non-uniformities on boundary layer combustion in a circular constant-area combustor. A Rectangular-to-Elliptical-Shape-Transition (REST) inlet, typical of the type of inlets proposed for self-starting scramjet inlets, was attached upstream of the combustor in the current experiments. To simulate ow disturbances that are representative of those generated by cross-stream fuel injection, vortex generators of semi-pyramidal shape were attached at several locations in the REST inlet. The skin friction drag on the inner surface of the combustor indicated a reduction of 30% when hydrogen burns in the boundary layer. These results show that the level of drag reduction is similar to that measured in tests without vortex generators. This therefore demonstrates that ow disturbances representative of those brought about by cross-stream fuel injection in the inlet do not aect the drag reduction potential of boundary layer combustion