Scramjet flowpaths employing elliptical combustors have the potential to improve structural efficiency and performance relative to those using planar geometries. NASA Langley has developed a scramjet flowpath integrated into a lifting body vehicle, while transitioning from a rectangular capture area to both an elliptical throat and combustor. This Rectangular-to-Elliptical Shape Transition (REST) scramjet, has a design point of Mach 7.1, and is intended to operate with fixed-geometry between Mach 4.5 and 8.0. This paper describes initial free-jet testing of the heat-sink REST scramjet engine model at conditions simulating Mach 5.3 flight. Combustion of gaseous hydrogen fuel at equivalence ratios between 0.5 and 1.5 generated robust performance after ignition with a silane-hydrogen pilot. Facilitymodel interactions were experienced for fuel equivalence ratios above 1.1, yet despite this, the flowpath was not unstarted by fuel addition at the Mach 5.3 test condition. Combustion tests at reduced stagnation enthalpy indicated that the engine self-started following termination of the fuel injection. Engine data is presented for the largest fuel equivalence ratio tested without facility interaction. These results indicate that this class of three-dimensional scramjet engine operates successfully at off-design conditions.

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A series of mean velocity and turbulence intensity surveys have been obtained for flow between the electrodes of a gas-flow spark gap switch over a range of gas pressures, gas species, and gap spacings for one electrode geometry consisting of two 3.81-cm-diam electrodes with domed tips placed transverse to the gas flow direction. Data include mean and fluctuating velocity profiles measured between the electrodes, both on the electrode axis and downstream of the electrodes. Pitot, total head, and one-and two-channel hot wire probes have been used. These data document flow conditions occurring in a gas-flow spark gap switch and provide insight into flow processes affecting recovery of such a switch when operated repetitively. Results have indicated that highly turbulent wakes are formed downstream of these electrodes; these wakes are believed to degrade switch electrical recovery due to trapping of heated debris from prior arcs. Also, it has been found that, for this electrode geometry, freestream turbulence levels do not have a great effect on recovery.Nomenclature d = interelectrode gap spacing / = longitudinal turbulence intensity, defined as rms x -velocity fluctuation divided by mean velocity p = gas pressure R = electrode radius U = streamwise mean velocity in x direction V = horizontal mean velocity in y direction x -horizontal coordinate, measured in direction of gas flow y = horizontal coordinate, measured transverse to direction of mean gas flow z = vertical coordinate, measured along electrode axis from midgap A = turbulence integral length scale (large, energycontaining eddy size) 1 = turbulence microscale (eddy size relating mean square strain rate fluctuation to mean square velocity fluctuation) T = switch recovery time for 70% recovery