Acceleration is the Key to Drag Reduction in Turbulent Flow

A turbulent pipe flow experiment was conducted where the surface of the pipe was oscillated azimuthally over a wide range of frequencies, amplitudes and Reynolds number. The drag was reduced by as much as 30%, higher than what was previously seen in a similar experiment. Past work has suggested that the drag reduction due to spanwise wall oscillation scales with either the velocity amplitude of the motion or its period. Here, we find that the key parameter is simply the acceleration. This insight opens new potential avenues for reducing fuel consumption by large vehicles and for reducing energy costs in large piping systems.