Investigation of alternative drag-reduction strategies in turbulent boundary layers by using wall forcing

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The aim of this research is to investigate, in an interactive programme involving several mutually supportive computational approaches and paradigms, the feasibility of achieving sustained and economically worthwhile frictional-drag reduction at flight Reynolds numbers using cross-flow wall forcing. While the emphasis of the programme is on the fundamental turbulence physics and the prediction of its interaction with wall drag, in general, the programme is closely associated with an important civil aviation goal, namely the reduction in emissions per passenger km by 50% by 2020. The programme will combine studies involving direct numerical simulations and highly-resolved large eddy simulations with two approaches based on linearised streak modelling, one developed by Chernyshenko (Imperial College) and the other by Lockerby (Warwick). The general strategy is to use the full-resolution schemes to gain insight into the near-wall turbulence mechanisms associated with frictional drag, to generate calibration-related input into the linearised streak modelling and to investigate the validity of this modelling for a range of actuation parameters examined with the full-resolution approaches. The proposed research is fundamental in nature and complements well EPSRC's Active Aircraft programme, which is practically-oriented. The ultimate objective is to derive a prediction procedure, based on linearised streak modelling that allows the effect of different configurations of cross-flow wall forcing on drag at flight Reynolds numbers to be quantified. The programme is financially supported by EADS.