Investigation of the Flow Establishment of Pre-Combustion Shock Trains in a Shock Tunnel

Abstract

This work is a fundamental investigation of the behavior of precombustion shock trains in the T4 Stalker Tube at the upper end of the dual-mode combustion regime. Experiments were conducted at a condition that represents flight at Mach 8 at an altitude of 26 km. The test model was a simple axisymmetric duct comprising a short diffuser, an isolator (length/diameter = 4.1), and a constant-area combustor (length/diameter = 15.7). Gaseous hydrogen was used as the fuel and was injected via six portholes equispaced around the perimeter of the duct. Time histories of the surface pressure in the model showed a pressure rise from stable supersonic combustion up to a fuel equivalence ratio of 0.9. At higher fuel levels, a precombustion shock train formed upstream of the point of fuel injection. Between equivalence ratios of 0.9 and 1.1, the shock train established itself and remained stable over a significant portion of the approximately 3 ms test window. Above an equivalence ratio of 1.1, the pressure time histories continued to rise throughout the test window and a stable flow was not established. These results indicate that short-duration facilities like the T4 Stalker Tube can be used for dual-mode combustion studies at fuel levels below a limit that will depend on the particular flow condition and model geometry.