Frohnapfel, B.

Hasegawa, Y.

Jovanovic, J.

Kasagi, N.

English

KITopen

Theoretical Considerations aboutNear-Wall Turbulence and ResultingFlow Control SchemesBettina Frohnapfel, Technical University DarmstadtJovan Jovanovic, University ErlangenYosuke Hasegawa, University of TokyoNobuhide Kasagi, University of TokyoSince turbulent drag consumes large amounts of energy its reduction is ofgreat economical and ecological interest. Our work aims at providing furtherunderstanding of the mechanism of viscous drag reduction.Based on analytical considerations about how near-wall turbulence needs to bemodified in order to reduce the momentum loss towards solid walls and to yieldlower energy losses, a mechanism of turbulent drag reduction is proposed. Thismechanism suggests that drag reducing flow control at high Reynolds numbersshould be designed to minimize the turbulent dissipation rate. A review andanalysis of existing DNS data bases for which drag reduction has been reportedshows that the proposed drag reduction mechanism is found for a variety ofdifferent flow control techniques. Based on the obtained knowledge we developactive and passive flow control schemes for viscous drag reduction.In respect to active flow control, we have developed a flow control loop basedon upstream sensing of the streamwise wall shear stress. Presently, a numericalassessment for the application of this control loop to skin friction control withplasma actuators is carried out.In the field of passive flow control we propose a tentative surface structure withgrooves aligned in the flow direction. The drag reducing performance of thesurface structure is tested experimentally by comparing the pressure drop in achannel with grooved surfaces with the one in a smooth channel. It is found thata significant reduction in pressure drop is only obtained for grooves in the orderof one viscous length scale, which corresponds to approximately the Kolmogorovscale of the flow.1

Theoretical considerations about near-wall turbulence and resulting flow control schemes

https://publikationen.bibliothek.kit.edu/1000029206/2227699

Theoretical considerations about near-wall turbulence and resulting flow control schemes

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