Simulations of a low-boom, axisymmetric, external compression inlet

The NPARC designed code, WIND-US, has been used in a study of low boom axisymmetric external compression inlets with and without throat slot bleed. To validate the Reynolds-averaged Navier-Stokes (RANS) approach to predict such flows, two simulations of an experimental slot bleed flow (with and without an oblique shock) from AIAA-95-0032 have been performed. A computational analysis was then conducted on WIND-US of three different axisymmetric inlets, designated C0, A4, and K1, designed to achieve low boom at Mach 1.70. All computations were run at Mach 1.67 to be consistent with the operational limits of the 8’x6’ NASA Glenn wind tunnel to be used in future experimental testing. A variety of different operating conditions and geometry modifications were investigated. It was found that the A4 inlet has the best recovery characteristics. However K1 has the possibility of attaining a more stable flow field without significant detriments in terms of pressure recovery. The inlet performance on the C0 is not significantly sensitive to Reynolds numbers. Small changes in Mach number on the C0 led to variations in the overall total pressure recovery, consistent with that expected from quasi 1-D shock relations. The overall ‘boom’ characteristics of the inlet did not significantly change when either the Reynolds or Mach numbers were altered. It was found that moving the cowl forward with respect to the centerbody reduced the boom signature of the inlet. The A4 was used to show that reducing the cowling angle significantly decreased the sonic boom signature. Given the presence of shock boundary layer interactions within the inlet, slot bleed was implemented on the centerbody of the K1 just downstream of the terminal normal shock. At the optimized plenum pressure, 25.1% of the freestream stagnation pressure, the bleed and solid wall cane curves behaved vary similarly. The slot leading edge geometry had little effect upon integrated recovery, but the elliptic leading edge was found to bleed more efficiently. Boom performance was very similar to that found with the solid wall geometry, however bleed has the ability to allow for stable operation at lower inlet mass flow ratios and thus lower boom levels.