Experimental analysis of friction drag above moving surfaces

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It is the objective of this research group to analyze the mechanisms that are responsible for turbulent friction drag and to develop a modern model-predictive closed-loop control system that is able to control turbulent friction drag using spanwise transversal surface waves. The investigation of turbulent boundary layers at steady inflow conditions was the major issue during the first funding period. In the second funding period, the focus will be on the question, to what extent unsteady and, hence, more realistic inflow conditions possess an influence on the drag reduction mechanisms and how these temporal perturbations can be compensated using spanwise transversal surface waves.The objective of subproject 1 is to determine the effect of periodic unsteady inflow conditions and of a positive pressure gradient on the turbulent boundary layer of smooth and structured flat plates with and without spanwise transversal surface waves. Hot-wire anemometry, particle-image velocimetry, wall-shear stress, and pressure measurements will be used to determine the significant mechanisms that are responsible for turbulent friction under these boundary conditions and to derive control variables that can be used to develop a model-predictive closed-loop control system that is able to reduce drag even at unsteady inflow conditions.