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Scramjet Combustor Measurements

In order for Supersonic Combustion Ramjets (scramjets) to be a viable vehicle, two main issues need to be adequately addressed: the relatively low residence time in the engine, and reduced fuel/flame propagation into the freestream of the engine. One solution is to implement wall cavity flameholders, which have been studied for some time as a means to extend the residence time in scramjet combustors. For particular cavity geometries, angling the rear wall was found to suppress periodic pressure fluctuations—providing steady flameholding. Additionally, placing a strut immediately upstream of the wall cavity augments mixing and flame propagation. Behind the strut a low-pressure region forms, which can be placed upstream of either a cavity or fuel injector to entrain fuel/air into the main flow, and it has been shown that a strut is an effective means of generating vortices, which can further augment mixing.

Due to the supersonic nature of the flow, the use of physical probes to determine the flow field is problematic due to the large disturbances they can cause. Therefore, a non-intrusive method which can adequately characterize the flow is necessary. Such methods normally consist of laser scattering measurements of particles that are added to the flow. However, since these particles tend to be significantly denser than the fluid medium they are suspended in, they fail to follow streamlines through large velocity gradients such as shocks. To avoid such inconsistencies, a molecular tagging velocimetry technique known as Hydroxyl Tagging Velocimetry (HTV) has been used to measure the velocity and vorticity over a 2D cross-section. Additionally, the major chemical species and temperature have been measured over multiple 1D lines through the wall-cavity using Line Raman Scattering.

Supersonic wind tunnel

Adapted from:
N. R. Grady, T. Friedlander, R. W. Pitz, C. D. Carter, and K.-Y. Hsu, “Hydroxyl Tagging Velocimetry in a Supersonic Flow over a Piloted Cavity,” 48th AIAA Aerospace Sciences Meeting, Paper No. AIAA-2010-1405, Orlando, Florida, January 4-7, 2010.