Spatially and Temporally Resolved Visualization of Turbulent Spots in Blasius Boundary Layer Transition

Kurzfassung

The temperature-sensitive paint (TSP) method is applied in a transitional flat-plate boundary layer flow in a low-speed laminar water channel. The long measuring times in this facility lead to strong requirements for the homogeneity of the heat flux between surface and flow, which is necessary for the visualization technique. Therefore, a special element to apply the visualization technique, which can be placed flexibly in the facility, was developed. The requirements concerning the homogeneity of the heat flux were fulfilled with a heating based on a current-carrying layer of carbon fiber. The TSP method was used to investigate the turbulent spots in the transitional region. In the present experiment turbulent spots are generated by the laminar-turbulent transition process. The transitional flow in the experiment was threedimensional because of flow control devices placed near the leading edge of the flat plate. The visualization of the occurring turbulent spots was time resolved and capable of resolving the flow structures of the turbulent spot close to the wall, i.e. inrushes caused by sweeps, hairpin vortices and streaks.