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Zach R. Murphree, K. Bulent Yuceil, Noel T. Clemens and David S. Dolling
Shock wave/boundary layer interactions (SWBLI) are a very important flow phenomenon. Both laminar and turbulent SWBLI have been extensively studied, but little is known about interactions where the incoming boundary layer is transitional, especially when the interaction is three dimensional. This study seeks to add to the fundamental understanding of such interactions.
The interactions are generated by a cylinder mounted on a flat plate (Figure 1). The bow shock of the cylinder interacts with the boundary layer of the flat plate, and the familiar, lambda-shaped interaction results.
Figure 1: Model schematic
The simplest way to tell which category the resulting interaction is in (laminar, transitional, or turbulent) is by looking at the streamwise distance from the leading edge of the cylinder to the separation line. Laminar separation distances are generally 6-12 cylinder diameters where turbulent separations are 2-3. Transitional separation distances are between the two. With surface flow visualization one can tell which type of interaction is occurring (Figure 2).
Figure 2: Surface flow visualization with kerosene-lampblack
Whereas the above surface visualizations provide a qualitative description of the mean flowfield, planar laser scattering (PLS) provides essentially the same information on an instantaneous basis. This is important because the transitional interactions are inherently unsteady. With our high-speed optical setup (10 kHz) we are able to see how the interaction changes in time and what effects these changes (Figure 3).
Figure 3: PLS image of transitional interaction
High-Speed particle image velocimetry (PIV) has also been used to get a more quantitative view of the interaction, as seen in Figure 4. The combination of surface visualizations, PLS, and PIV suggest that in a transitional interaction there is a small, intermittent �laminar� shock upstream of the turbulent separation region. The growth and collapse (Figures 5 and 6) of this laminar separation bubble could contribute to the increased unsteadiness of the transitional interaction.
Figure 4: Streamwise velocity contours obtained with PIV
Figure 5: Presence of laminar separation causes weak separation shock upstream of "turbulent separation"
Figure 6: Separation bubble collapses leaving only "turbulent separation" bubble
Ongoing Work
Ongoing work will include installation of wall fences to reduce possible sidewall interference, IR thermography to determine how transition the natural transition location changes in the presence of the interaction, and centerline pressure measurements to quantify the time and length scales of the unsteadiness and verify the existence of the upstream laminar separation mentioned above.
Publications:
Experimental Studies of Transitional Boundary Layer Shock Wave Interactions, Murphree, Z.M., Yuceil, K.B., Clemens, N.T., and Dolling, D.S., AIAA-2007-1139, 45th Aerospace Sciences Meeting, Jan. 8-11, Reno, NV
Experimental Studies of Transitional Boundary Layer Shock Wave Interactions, Murphree, Z.M., Jagodzinski, J., Hood, E.S. Jr., Clemens, N.T., and Dolling, D.S., AIAA-2006-326, 44th Aerospace Sciences Meeting, Jan. 9-12, Reno, NV
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