Unsteady Experimental and Numerical Analysis of a Low-Boom Inlet

Reducing the produced sonic boom during supersonic flight is critical for future commercial flight over land, motivating “low-boom” aircraft design. A low-boom concept inlet utilizing a relaxed isentropic compression spike and a zero-angle cowl has shown to significantly reduce external overpressure and to increase pressure recovery in the downstream diffuser. A large experimental data set was gathered at the 8’ x 6’ supersonic wind tunnel at NASA Glenn Research Center in 2010 which illustrates a dynamic normal shock at near-design mass flow conditions. Much of the previous work on this inlet has focused on evaluating performance, reduction in sonic boom, and micro flow control device effects, leaving the normal shock unsteadiness at near-design conditions largely uninvestigated.
The current study aims to determine the cause of the normal shock unsteadiness observed at near-design mass flow conditions. A Detached Eddy Simulation (DES) approach is used to generate numerical results to better understand the inlet flow-field. Grid resolution and computational domain length effects are investigated and compared with unsteady and time-averaged experimental data. Compression wave propagation throughout the subsonic diffuser is tracked using unsteady experimental surface pressure taps. These results and the detailed flow description from the DES help to identify streamwise propagating waves and their role in shock unsteadiness. Understanding the source of the normal shock motion and the mechanics of streamwise waves in the diffuser may lead to flow control methods to increase shock stability and, in turn, inlet performance.