Complex Wake Flows

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Modern commercial transport aircraft use slotted flap systems for obtaining high lift coefficients during low-speed flight. The wakes of slats and main wings present in these configurations are subjected to the adverse pressure gradient and streamwise flow curvature, both induced by the respective trailing wing element. The adverse pressure gradient generates a strong lateral increase of wake width and sometimes even embedded regions of reverse flow. This reduces the lift coefficient and limits maximum lift. Precise predictions of these effects are presently not possible as there is a lack of a trustworthy data base and hence, detailed validation of current flow models used in aircraft design is impossible. The objective of the present research project is to establish a comprehensive data base of wake flows at high Reynolds numbers with strong adverse pressure gradients. While the canonical case of a symmetrical wake with and without adverse pressure gradient was thoroughly investigated in the preceding DFG-RBRF Project “Wake Flows in Adverse Pressure Gradient”, the proposed follow-on project will create a sound data base for the more general canonical flow case of the curved wake under adverse pressure gradient. Turbulence resolving simulations and detailed flow measurements by optical means will generate the detailed balance of the Reynolds stress equations along the curved wake flow path. The turbulence data will be used to derive physics-based extensions to the stress equations and the transport equation governing the turbulence length scale. Two Reynolds-stress models of turbulence will be extended in that way, and identification of the model extensions with the lowest model error and their calibration will be accomplished by methods of Uncertainty Quantification based on Bayesian Inference. The project will validate the improvement of the Reynolds-Stress models of turbulence for predicting the high-lift performance of a slotted wing section. Therefore, the project will establish a turbulence-resolving data base for the three-element airfoil MD 30P-30N, for which flow field measurements of the wake are available from literature. The research work of the project will be shared between three renowned research teams. The team of St Petersburg Polytechnic University will undertake hybrid turbulence resolving simulations, whereas TU Braunschweig will perform detailed wind tunnel experiments. RANS modelling and its validation will be shared by TU Braunschweig and the DLR team in Göttingen. Comprehensive comparisons of wind tunnel data, hybrid RANS/LES simulations, and the extended RANS models will advance the state of the art in a very challenging application field of modern aerodynamics.