Drag reduction measurements in an azimuthally oscillating turbulent pipe flow

Spanwise oscillating surface elements have been widely studied as a means
of drag reducing turbulent flow control; however, much is still unknown
about the underlying mechanism resulting in drag reduction. Experimental
studies in an azimuthally oscillating turbulent pipe flow were conducted
across a wide range of oscillation frequencies, amplitudes, and Reynolds
numbers. In comparison to previous work, the parameter space has been
considerably expanded to provide deeper insight into the relationship
between various key parameters and drag reduction. Drag reduction
measurements are presented with corresponding key parameters: the
non-dimensional period of oscillation, the non-dimensional velocity
amplitude of oscillation, the friction Reynolds number, and a new
parameter, non-dimensional acceleration of oscillation.