A rectangular strut on the expansion ramp of a scramjet thruster for thrust vector control

Cold flow experiments were conducted on a laboratory model of a scramjet thruster consisting of a rectangular strut spanning the width of the expansion ramp of the model. The cross section of the strut was square. The strut was placed at halfway of the ramp length. The experiments were conducted at six different thruster pressure ratios (TPR) i.e., the ratio of inlet total pressure to ambient pressure-ranging from 5 to 10 at each of six strut heights. The internal wall pressure distributions of the thruster and schlieren images of the flow obtained from experiments were examined. The possibility of using the strut as a supplementary device in the thruster for the control of a hypersonic vehicle which normally employs aerodynamic control was studied. The inlet Mach number of the combustor was 1.8. The thruster model consisted of an isolator, a diverging area combustor and a single expansion ramp. The inlet flow to the thruster was provided by a supersonic nozzle with a rectangular exit of matching dimensions to the rectangular isolator. The diverging combustor was of rectangular cross section, the bottom wall being flat and the upper wall making an inclination of 2.44(o) to the bottom wall. From the top and bottom wall pressure distributions, two-dimensional internal force coefficients and pitching moment coefficients were calculated and variation of these coefficients with strut height were studied. Larger strut heights caused an increase in side force coefficient at all expansion levels of the ramp nozzle i.e., for all the TPRs employed in the present work (5-10). The variation of pitching moment coefficient with strut height exhibited the similar behavior as that of the side force coefficient. Shifting of strut position from expansion ramp tail end to the ramp mid position did not affect the nature of these variations. These variations were in general nonlinear in nature but the degree of non-linearity varied based on the value of TPR. Larger non linearity in side force coefficient variation was observed at TPRs 5,9 and 10. Larger moment coefficients resulted at lower TPR for the mid ramp position of the strut when compared to ramp tail end position. Large strut heights caused noticeable downward deflection of ramp surface flow. Calculations using the experimental data on wall pressure in the range of strut height variation employed in the present experiments indicate that increments up to 12% in moment coefficient, 20% in side force coefficient and 4% in axial force coefficients were achieved when the strut height was increased to its maximum value (12% of combustor entry section hydraulic diameter). Schlieren images show that the exhaust flow over the expansion ramp suffered a downward deflection and the strut position & height affected the magnitude of the deflection.