Density field studies of a supersonic shear layer using non-intrusive optical methods

The performance of aircraft which use optical systems is dependent on analysis and modeling of the aero-optical distortions produced by the flow features surrounding these vehicles, particularly shear layers. Prior experimentally produced and simulated shear layer data indicate the presence of sharp density gradients in the flow which were previously not observed, and, according to some modeling arguments, assumed to be nonexistent. Further study of shear layer density fields is needed in order to properly develop physics-based models of their aero-optical effects, and to achieve better agreement between simulated and experimental results. Here, results are presented from Planar Laser-Induced Fluorescence (PLIF) and Self-Aligned Focusing Schlieren (SAFS) measurements, which serve to quantitatively and qualitatively describe the density field and/or the gradient of density along a wall-normal plane. These measurement techniques were applied to a shear layer with one side having a transonic velocity with a Mach number of 0.95, and the other having a supersonic velocity with a Mach number of 2. Both sides consisted of air, with matching stagnation temperatures of approximately 300K.