Adam J. Pierce

Experimental Study of Near Wake of Micro Vortex Generators in Supersonic Flow

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.

Numerical and Experimental Studies on the Separation Topology of the MVG Controlled Flow at M=2.5

In this paper, the implicitly implemented LES method and fifth order bandwidth optimized WENO scheme are used to make comprehensive studies on the separation topology of the MVG controlled flow at M=2.5 and Re{\theta}=5760. Experiments are also made to verify the prediction of the computation. Analyses are conducted on three categories of the topology: the surface separation, cross-section separation and the three dimensional structure of the vortices. A complete description about the separation topology and a series of new findings are obtained. Among them, a pair of spiral point is first predicted by the computation and verified by the experiment. A corresponding new vortex model with 7 vortex tubes is presented also.

Review of Micro Vortex Generators in High-Speed Flow

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.

Experimental and Numerical Study of Flow Topology Past Micro Vortex Generators

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.

New Developments in Surface Oil Flow Visualization

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.

New Seeding and Surface Treatment Methods for Particle Image Velocimetry

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.

Laser Alignment Method for Portable Schlieren System

Astigmatism and coma are two optical aberrations that are common with Z-type schlieren systems. The effects of these two aberrations can be minimized by increasing the accuracy in the optical alignment of all optical components of the system. For portable schlieren systems, the alignment process can become a time-consuming task every time the system is relocated. A portable schlieren system utilizing alignment lasers and newly designed mirror mounts was developed. The system can be set up rapidly and accurately.

Interaction of Microvortex Generator Flow with Ramp-Induced Shock/Boundary-Layer Interactions

This paper reports the experiments conducted using two di erent micro vortex generator design on a at plate with four con guration at Mach 2.5. Con gurations include a at surface (baseline), 5 degree ramp, 25 degree ramp, and a 1 in. diameter cylinder. Surface ow and schlieren were applied experimentally and high-order LES was applied numerically. Results suggest that MVGs have a practical upper limit to their e ectiveness 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 e ects of micro vortex generators.

Numerical modeling of doorway flow induced by an air curtain

A large cabin was partitioned along its centerline with the two sides were connected by a doorway. An air curtain was mounted just in front of the doorway. Directly below the air curtain, on the floor, is a vent for receiving the air curtain flow. The air curtain flow was modeled by a commercial Reynolds-averaged Navier-Stokes flow solver with a k-ε turbulence model. The simulation showed that the longitudinal velocity profile of the jet was well maintained from the top to the bottom of the doorway, with a small amount of lateral diffusion. However, the transverse velocity profile showed a larger amount of diffusion. The results indicated that the floor vent did not properly capture the air curtain flow, resulting in entrainment of the air curtain flow into the cabin. Thus, a detailed design of the floor vent is required for certain applications, such as next-generation explosives detection portals, where as much of the air curtain flow as possible needs to be captured.

Velocity Measurements of Doorway Flow Induced by an Air Curtain

The airflow induced by an air curtain mounted over a doorway is examined for its potential use in explosive detection portals. A challenge to gaining understanding of such flows is mapping it using particle image velocimetry (PIV), a technique which is usually used in smaller-scale applications and with higher velocity flows. This paper discusses some of the challenges, requirements, techniques, and results of mapping large-scale flows with PIV, in particular, the mapping of a doorway flow induced by an air curtain.