Computational Aerodynamic Predictions of Supersonic Retropropulsion Flowfields

Abstract

Supersonic retropropulsion, or the initiation of a retropropulsion phase at supersonic freestream conditions, is an enabling decelerator technology for high-mass planetary entries at Mars. Supersonic retropropulsion relies on retrothrust to decelerate the vehicle. A thrust-driven interaction of underexpanded jet flow with the shock layer of a blunt body alters the aerodynamic characteristics of the vehicle. Little literature exists on analytical and computational modeling approaches for supersonic aerodynamic-propulsive interactions at moderate thrust levels and flight-relevant conditions. This investigation is an exploratory application of a steady, turbulent computational approach to supersonic retropropulsion flowfields using modern and historical test cases. The results obtained from this approach agree reasonably well with experimental data for the locations of the bow shock, stagnation point, and Mach disk for a retropropulsion configuration with a single nozzle at the nose. The surface pressure distributions agree less favorably, showing a pressure rise toward the shoulder that was not observed in the original experiment. The flowfield structures for a peripheral retropropulsion configuration agree qualitatively with the expected structures, but proper inboard jet flow expansion and interactions between individual jet flows are likely not being captured; accordingly, pressure is preserved inboard of the nozzles to higher thrust than was observed experimentally.