REDUCING DRAG IN TURBULENT PIPE FLOW BY AZIMUTHAL WALL OSCILLATION

An oscillating pipe flow experiment is performed to examine drag reduction behavior in high Reynolds number flows. A novel experimental set-up allows for a large range of oscillation amplitudes, frequencies, and friction Reynolds numbers (ranging from 856 to 5744). A maximum drag reduction of 31% is reported. The results support the suggestion that the key scaling parameter is the non-dimensional acceleration of the surface oscillation, which collapses all the data regardless of Reynolds number, actuation frequency, and actuation amplitude. This scaling holds for non-dimensional periods of oscillation down to approximately 100, which corresponds to the value that is commonly proposed to achieve the maximum level of drag reduction.