Numerical investigation of scramjet inlet models for side spillage reduction

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This study introduces and evaluates five models of Mach 7 scramjet inlets designed to reduce side spillage. The baseline model is characterized as a 2D-wedge type inlet without sidewalls. To mitigate interference from expansion waves, an alternative model featuring a converging angle identical to the freestream Mach angle is proposed. Another inlet model presents each ramp's converging angle matched to the local Mach angle of its respective ramp. Subsequently, an inlet model with sidewalls attached to the baseline model is introduced, and an additional inlet model is presented with reduced-height sidewalls. Three-dimensional Reynolds-Averaged Navier-Stokes simulations are conducted for each inlet model, and the performance of the inlets is compared. The mass flow averaged properties at the isolator exit for each inlet model are computed. To evaluate the performance of engines equipped with each inlet model, thrust and specific impulse are determined using thermodynamic cycle analysis. Ultimately, net thrust is calculated by subtracting drag from thrust, and the results are compared. The inlet with converging ramps, which has the largest captured area, indicates the lowest net thrust, amounting to 38% of that of the baseline model. In contrast, the inlet with reduced height sidewalls represents the highest net thrust, which is 3.5 times that of the inlet with converging ramps. These results demonstrate that for scramjet inlet design, using sidewalls to reduce drag is a more effective method for reducing side spillage compared to employing converging ramps with a large captured area.