Abstract
The effect of a spanwise traveling-wave motion on a zero-pressure-gradient turbulent boundary layer over a flexible sheet was investigated. The test plate placed in wind tunnel consisted of a flexible sheet section, where the traveling wave motion was generated by the vibration device with a crank, and the upstream and downstream smooth rigid wall sections. Velocity profiles were measured by single and cross hot-wire anemometry. Amplitude and frequency of the traveling wave motion were measured using two laser displacement sensors. The drag reduction ratio was estimated from the friction coefficients through the growth rate of the momentum thickness of the turbulent boundary layer over the flexible sheet section. The maximum drag reduction of up to 13% was obtained. The quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that the drag reduction was attributed to the reduction in the sweep event and the increase in the negative contribution of the inward-interaction event to the Reynolds shear stress due to the sheet displacement fluctuation.
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