Investigations of cascaded micro-blowing for drag reduction in turbulent boundary layers

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The present proposal is part of an intended international cooperation with the Khristianovich Institute of Theoretical and Applied Mechanics of the Russian Academy of Science, Siberian Branch. The Russian partner will apply for his share of the funding at Russian Foundation of Basic Research.The purpose of the present proposal is to revive the concept of micro-blowing for turbulent skin friction drag reduction. This appears feasible because modern materials and new production methods allow manufacturing of micro-perforated smooth surfaces which do no longer exert additional roughness-induced drag on the main flow. Using a very recent observation of the Russian partner (obtained so far for a single blowing panel only) cascading of such panels in streamwise direction will lead to a considerable reduction of blowing mass-flow rates for a given drag reduction effect, i.e. a remarkable efficiency increase which has not been studied so far.The problem will be investigated using two complementary techniques: Detailed laboratory experiments with the latest flow-diagnostics devices in Russia and direct numerical simulations on a high-performance computer system that delivers insightful data that are not biased by a possibly inappropriate turbulence model in Germany. Very unique results can be expected allowing to extract new qualitative and quantitative information of great fundamental and practical importance. Prediction and modeling of boundary-layer control using micro-blowing will be improved and data for validation of turbulence models will be obtained, for the first time for this problem. The related considerations are pioneering in many aspects and address important aspects of drag reduction for fuel savings and hence minimizing pollution of the environment.