Characterization of Supersonic Flow Interaction with a Shockwave Using Laser-based Diagnostics

Abstract

Experimental and computational studies were performed to investigate the effects of an incident shockwave on the flowfield and fuel distribution within a cavity flameholder. Shadowgraphy was used to characterized the flowfield in around a cavity and planar laser-induced fluorescence of the NO molecule was used to characterize fuel injection from a port upstream of the cavity. These experimental data were compared against CFD solutions of the Reynolds Averaged Navier-Stokes equations. The effect of the incident shock on the cavity shear layer controls fuel distribution within the cavity. The shock-on-jet impingement location pushes the shear layer deeper into the cavity and results in a higher concentration of fuel in the cavity. Shock-on-cavity impingement lifts the shear layer above the cavity and stretches the fuel plume in the spanwise direction. Increasing fuel injection momentum ratio does not strongly affect the flowfield in the presence of shocks.

Velocimetry Measurements of a Scramjet Cavity Flameholder with Inlet Distortion

“…These locations correspond to the resulting oblique shock wave impinging on the cavity, the jet injector, and a location upstream of the jet injector, respectively. This behavior of the shock wave was confirmed via a prior shadowgraph analysis [23], as seen in Fig. 2.…”

“…Substantial changes are also seen in the path lines, with reverse (−x direction) flow filling nearly the entire measurement plane. Though the limited field of view prevents its full characterization in the present study, numerical analysis indicated that this region does not support the kind of organized recirculation seen in the preceding cases [23].…”

“…7 suggest most, if not all, of such fuel would be immediately convected into the main duct flow without entering the recirculation region if the cavity flowfield is spanwise uniform. In a prior investigation with this same flowpath and distortion configuration, combustion could not be initiated with fueling from the ramp face [23]. CFD analysis of the same configuration suggested that short residence time and low static pressure near the sparkplug ignition sources may have been primarily responsible for the observed lack of ignition [22].…”

“…Spanwise flow patterns were also suggested by numerical analysis of this flowpath under distorted-flow conditions [22]. Attempts in previous work to sustain combustion at the shock-oncavity condition were successful both with and without fueling through the jet injector in addition to the cavity ramp [23], so it is clear that this mode of cavity operation does not preclude stable combustion. CFD analysis indicated that this configuration results in relatively high pressures in the cavity, thus enhancing flameholding potential [22].…”

“…This configuration was previously characterized experimentally using planar laser-induced fluorescence of the OH and NO species [22,23]. Apart from the inclusion of a distortion generator and the use of a Mach 3 nozzle in place of a Mach 2 equivalent, this flowpath is the same as that studied by Tuttle et al, who found that the shear layer did not reattach to the cavity floor [17], confirming the expected behavior based on the cavity length-to-depth ratio of 4.0.…”