Validation experiment on the transition of three-dimensional boundary layers on wings with spanwise varying flow conditions

• Applicant: Professor Dr.-Ing. Rolf Radespiel
• Subject Area: Fluid Mechanics
• Term: from 2010 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 162041067

Transition prediction is important for future laminar wing development for transport aircraft. Nowadays industrial design tools for stability analysis of the boundary layer use local data with the assumption of invariant flow conditions in spanwise direction. These assumptions are not generally valid on real wing configurations, and limit the accuracy of transition prediction. Until today there exist no experimental data to quantify the expected inaccuracy. The aim of the research project is to design and to conduct validation experiments on the transition on a swept wing with spanwise varying mean flow. The transition location is measured with infrared thermography over the whole area of the wing and is used to monitor crossflow vortices and their spanwise development. Possible dispersion effects in the area of wing sweep variations are investigated. Frequency spectra and the amplification of boundary layer instability modes are measured with hotfilm arrays.During the first project phase these measurements were performed in a medium size university wind tunnel, at Reynoldsnumbers of 2.75 million and with conventional levels of freestream turbulence. In the second phase the transition investigations will be particularly focussed at wing areas with spanwise varying crossflow instabilities. By performing these measurements in the larger DNW-NWB wind tunnel, significantly larger Reynoldsnumbers and lower freestream turbulence levels are obtained. This will add value to the resulting data base.

• DFG Programme: Research Grants
• Participating Institution: Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) ; Institut für Aerodynamik und Strömungstechnik