Transition control by suction at Mach 2

Different concepts of laminar flow control for supersonic swept wing flows are currently investigated in the EU project SUPERTRAC (SUPERsonic TRAnsition Control). For subsonic and transonic flight Mach numbers the feasibility and potential benefits of laminar flow control by suction have been evaluated and demonstrated in several wind tunnel and flight experiments already. For supersonic flows, however, comparable experience and knowledge is not available yet. Therefore, in SUPERTRAC work package 3 experimental and numerical studies on laminar flow control by suction for a infinite swept wing configuration at Mach 2 were performed. The Ludwieg Tube Facility (RWG) at DLR Göttingen with a test section of 0.34m x 0.35m was used for these experiments. Hence, a rather small wind tunnel model was required and the measurements had to be performed at relatively high freestream unit Reynolds numbers which introduced some additional complexity for the design of the wind tunnel model. Therefore, a comprehensive numerical trade-off analysis was required in preparation of the wind tunnel experiments to define a wind tunnel model and test conditions which meet the different and partly conflicting requirements best. N-factor computations have been performed for different freestream conditions, relative profile thicknesses and sweep angles of the wing. Both sharp and blunt leading edges were considered. Moreover, the suction rates, the position and the downstream extend of the suction panel were varied systematically. The work was shared between the project partners. These numerical data were used to select a suitable model configuration for the RWG experiments. Finally, a biconvex profile with sharp leading edge and a relative thickness of 13 percent was chosen. The measurements have been performed for sweep angles of 20 and 30 degrees. Suction was applied between 5 and 20 percent chord through a suction panel made from sinter material of relatively high porosity. With this setup a significant delay of transition by suction could be achieved in the experiment. Results from the preparatory numerical study, the wind tunnel experiment and the subsequent numerical analysis of the experimental data will be presented. The latter is still in progress, but e.g. should provide information on the dependence of the transition N-factor on the suction rate. The work presented is part of the European research project SUPERTRAC under contract No. AST4-CT-2005-516100. The authors are grateful to all SUPERTRAC partners for their contributions to the results discussed