Boundary layer transition

The boundary layer stability, its active control by sound and surface heating and the effect of curvature are studied numerically and experimentally for subsonic flow. In addition, the experimental and flight test data are correlated using the stability theory for supersonic Mach numbers. Active transition fixing and feedback control of boundary layer by sound interactions are experimentally investigated at low speed over an airfoil. Numerical simulation of active control by surface heating and cooling in air shows that by appropriate phase adjustment a reduction in the level of perturbation can be obtained. This simulation is based on the solution of two-dimensional compressible Navier-Stokes equations for a flat plate. Goertler vortices are studied experimentally on an airfoil in the Low Turbulence Pressure Tunnel (LTPT). The flow pattern was visualized using the sublimating chemical technique and data were obtained using a three component laser velocimeter. The effect of curvature on swept leading-edge stability on a cylinder was numerically studied. The results suggest that transition is dominated by traveling disturbance waves and that the waves with the greatest total amplification has an amplitude ratio of e sup 11. Experimental data from the quiet supersonic tunnel and flight tests are analyzed using linear compressible stability theory

Research in Natural Laminar Flow and Laminar-Flow Control, part 2

Part 2 of the Symposium proceedings includes papers addressing various topics in basic wind tunnel research/techniques and computational transitional research. Specific topics include: advanced measurement techniques; laminar flow control; Tollmien-Schlichting wave characteristics; boundary layer transition; flow visualization; wind tunnel tests; flight tests; boundary layer equations; swept wings; and skin friction

An Experimental Investigation of the Effect of Narrowband Freestream Noise on Fundamental Transitional Shockwave-Boundary Layer Interaction Mechanisms

Recent work at the University of Tennessee Space Institute has demonstrated that the resonant behavior observed in the spectra of cylinder- and blunt-fin-generated XSBLIs is connected to fundamental fluid mechanisms within the boundary layer. Therefore, a test campaign was conducted to characterize the fundamental mechanisms that drive the low-frequency unsteadiness in cylinder- and blunt-fin-generated shockwave-boundary layer interactions, specifically shockwave-boundary layer interactions in which the incoming boundary layer is undergoing a laminar-to-turbulent transition. This research aims to develop a deeper understanding of such interactions and characterize the resonant behavior observed in past work by varying the sweepback angle of a hemicylindrical blunt fin in the UTSI Mach 2 Blowdown Facility. A z-type schlieren setup provided a qualitative understanding of the flowfield. Quantitative results were extracted from the qualitative images using image processing techniques developed within MATLAB. Previously reported freestream narrowband noise in the University of Tennessee Space Institute Mach 2 Blowdown Facility was measured in the spectral content of the leading-edge shockwave and in the boundary layer. The unswept case showed excellent agreement with previously reported results. However, the swept blunt-fins did not exhibit the same narrowband spectral content as the unswept blunt-fin, but instead showed a broadening of the spectral content as the sweep angle was increased. Additionally, the scale of the interactions decreased, as expected, with the reduction in shock strength. Furthermore, the calculated Strouhal numbers for the swept fins showed excellent agreement with prior research