Transition strips on Wings
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Transition strips on wings
Use of local-flow conditions for calculation of roughness-particle height in transition strips on wings – Transonic Aerodynamics
This methodology is based on that of van Driest and Blumer, which enables the required height of roughness elements in a boundary-layer transition band to be estimated from the local boundary-layer displacement or momentum thickness, together with conditions at the edge of the boundary layer. The item is accompanied by a GUI-based program which, when used in conjunction with a coupled integral-boundary-layer aerofoil or wing /body code (e.g. VGK or VFP), permits rapid evaluation of the required roughness height over a range of test conditions.
The use of transition (or roughness) strips (or bands) to induce transition in wind-tunnel testing is well established. An example of such a strip, which typically consists of roughness elements (such as carborundum particles) locally glued to the surface, is shown in Sketch 1.1. When using this technique it is important that the roughness height, in the transition strip, is sufficient to establish transition fully at the desired location. However, use of excessive roughness height will thicken the turbulent boundary layer, resulting in excessive drag.
The software also provides the option determine the required roughness height to fix transition on a simple equivalent flat plate.