Detailed schlieren and laser lightsheet visualizations of the near wake of micro vortex generator (MVG) revealed large structures that were different from those of the undisturbed turbulent boundary layer. These structures were attributed to the rapid breakdown of the primary trailing vortex pair. The breakdown was thought to arise from a cylindrical Kelvin-Helmholtz-like instability surface. The structures appear to be hairpin or ring-like in nature that showed eruptions into the freestream flow, entraining it.

Detailed experimental and numerical visualizations of the flow past a micro vortex generator (MVG) in the form of a ramp with swept sides in a Mach 2.5 flow revealed a complex near-field topology. The incoming flow separated over the leading edge of the MVG despite the ramp angle being below the threshold for incipient separation. The separation over the MVG protuberance produced a weak trailing horseshoe vortex system. The attachment line shows a saddle/foci combination on each side of a nodal point of attachment. The flow over the top of the MVG separated off the slant edges to produce a large primary vortex pair. This large primary vortex pair induced two secondary vortex filament pairs, one off the top of the MVG and another at the corner of the MVG with the flat plate. Extra complexities were revealed at the trailing edge with at least two pairs of saddle/foci combinations observed. It is postulated that vortex filaments spring from the various saddle/foci combinations as these were not observed experimentally or computationally. Symmetry breaking due to flow unsteadiness was also observed in the MVG wake.

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A review of the state-of-the-knowledge of micro vortex generators (MVGs) and their effect on separated shock/boundary-layer interactions is provided. MVGs are thought to be effective for reducing the separation zone. However, details of how they affect the separation zone remain to be understood properly. In addition, metrics on how the MVGs affect the separation have not been well developed. Suggestions for further study are provided.

In this paper, the implicitly implemented LES method and fifth order bandwidthoptimized WENO scheme are used to make comprehensive studies on the separation topology of the MVG controlled flow at M=2.5 and Re θ

The prolific application of digital imaging and image processing for studying flows is extended to surface oil flow visualization. The use of colored, fluorescent mixtures enable bright, high-contrast images to be obtained which facilitate image processing. Examples were provided in visualizing the surface flow past micro vortex generators. Image processing of video sequences revealed minute features that are critical in understanding the flow.

PIV systems rely on a combination of seed particles, laser light intensity, and camera positioning to collected velocity data. Careful attention is needed when selecting the appropriate setup configuration for PIV systems. This paper focuses on several areas for improvement in PIV data collection for a compressible turbulent boundary layer study on a flat plate using MVG's. The topics include determining the seed particle surface preparation for a flat plate, and PIV system configuration. Nomenclature α divergence angle d laser beam diameter f focal length d p particle diameter ρ p particle density µ dynamic viscosity τ particle relaxation time

This paper reports the experiments conducted using two different micro vortex generator design on a flat plate with four configuration at Mach 2.5. Configurations include a flat surface (baseline), 5 degree ramp, 25 degree ramp, and a 1 in. diameter cylinder. Surface flow and schlieren were applied experimentally and high-order LES was applied numerically. Results suggest that MVGs have a practical upper limit to their effectiveness on ramp-induced shock/boundary-layer interaction which may be design dependent. The results also suggest the existence of vortex ring production and boundary layer growth due to the effects of micro vortex generators.