OPTICAL INVESTIGATION OF TURBULENCE MODULATION IN AN EXTERNALLY FORCED, HIGH REYNOLDS NUMBER BOUNDARY LAYER

An optical investigation of an externally forced boundary layer is presented. Measurements were conducted in Notre Dame’s Compressible Shear Layer Facility. The forced shear layer created an organized spatially-temporally-varying external flow outside the boundary layer. Full phase-locked 2D optical wavefronts were taken and compared with the previously-collected phase-locked velocity data. Local increase in temporal variance of the wavefronts was found to be associated with a local increase in turbulence intensity due to turbulence amplification events inside the boundary layer. Discrepancies between the amplitudes of optical distortions, experimentally measured and predicted using the Strong Reynolds Analogy, indicated that the pressure fluctuations inside the turbulence amplified regions are not negligible and contribute to the optical distortions. An updated model with included pressure-related terms is derived and it was shown to correctly predict experimental optical results.