Investigation of Unsteady/Quasi-Steady Scramjet Behavior using High-Speed Visualization Techniques

Abstract

Experiments are carried out in the HEG (High Enthalpy Shock Tunnel Göttingen) windtunnel to obtain detailed measurements on the HyShot II scramjet configuration at equivalence ratios close to the incipient choking point at simulated 28-km altitude flight conditions. Diagnostic techniques include time-resolved pressure measurements and simultaneous high-speed schlieren and OH* chemiluminescence imaging. Similar to previous experiments at higher equivalence ratios, the onset of choking is signaled by the formation of an unsteady shock train that initially propagates up the duct. The shock motion then slows, however, and a quasi-steady topology develops with the shock lodged at a position that depends strongly on the equivalence ratio (the position lying further upstream for higher equivalence ratios). This topology persists until the conclusion of the steady test time. Based on these measurements, a value for the critical choking equivalence ratio, i.e., that at which the shock train first appears, in the range of 0.38-0.39 is determined. High-speed temperature sensitive paint measurements are also carried out on the model intake ramp to provide global information on the boundary-layer transition behavior.

Incipient thermal choking and stable shock-train formation in the heat-release region of a scramjet combustor. Part II: Large eddy simulations

“…Specifically, the LES computations use the nominal shock tunnel conditions from the earlier experimental HyShot II campaign [10,11]. As explained by Laurence et al [12,15], however, the shock tunnel conditions in the most recent experimental study differ slightly, by about 5% in the stagnation pressure. This discrepancy is partially accounted for here by scaling the experimental pressure data by the ratio of the stagnation pressures.…”

“…10 and compared to the results from the experiments [12,15]. For both the LES and the experiments, the uncertainty due to variations in position over the finite time extent is estimated and shown in the figure.…”

“…It was later the subject of multiple experimental investigations in the High Enthalphy shock tunnel Göttingen (HEG) of the German Aerospace Center (DLR) [9][10][11][12][13][14][15]. The flow in the HyShot II combustor has been studied computationally by at least three different groups.…”

“…Thus the streamwise x coordinate is offset by 57.5 mm compared to the coordinates used in the experiments [10][11][12][13]15] and RANS simulations [16][17][18][19][20] performed at DLR.…”

Development of Dynamic Force Measurement Capabilities at AEDC Tunnel 9

“…The frequency response of conventional strain gauge balances is typically below 30 Hz so that the high sensitivity and low crosstalk requirements for such measurements are met, however this range is insufficient for accurate measurement of transient loads during impulsive events such as the unstart of scramjet inlets, 1, 2 mode switching, 3 shroud separation, 2, 4, 5 stage separation, 6 and divert thrusters firing. 7 These dynamic events involve large unsteady forces on millisecond timescales and are generated by complex flow physics such as shock interaction and boundary layer separation which pose considerable modeling challenges.…”