Near-On-Design Unsteadiness in a Supersonic Low-Boom Inlet

Abstract

The data collected in the supersonic wind tunnel at the NASA John H. Glenn Research Center of a low-boom supersonic inlet have been analyzed and compared to computational results generated using a detached eddy simulation methodology based on the Nichols–Nelson model. The objective of this study is to better understand the capability of this methodology and the source of significant external shock oscillations. The external-compression axisymmetric inlet includes a relaxed-compression spike followed first by a short subsonic diffuser to the aerodynamic interface plane that represents the inflow face of an engine and then by a long low-speed diffuser that terminates in the mass flow plug. The flow conditions for the experiments and simulations were based on a Mach 1.67 freestream coupled with 4.5% spillage (higher than the 1.5% on-design spillage condition). A 10 deg flow sector was modeled with a three-dimensional structured grid and solved with the WIND-US code. The time-averaged computational flowfield was not sensitive to including the low-speed diffuser domain, but this extra length was important for unsteady characteristics (especially pressure waves). Computations and experiments showed these waves originated downstream and propagated upstream, initially as weak acoustic waves, but led to strong pressure oscillations due to shock motion, as well as significant complexity in the transonic region near the throat.