Vorticity statistics and distributions in drag reduced turbulent pipe flow with transverse wall oscillations

Presented are vorticity statistics in drag reduced turbulent pipe flow at low and moderate Reynolds number. Drag reduction is achieved by transverse wall oscillations. Quantities of interest are the distributions of streamwise vorticity in the viscous and lower part of the buffer layer of the flow. We observe a sinusoidal pattern appearing in the distribution that is associated with the strengthening and weakening of counter-rotating vortex pairs. Presented alongside the phase varying distributions of vorticity are the phase averaged distribution of azimuthal and radial velocity fluctuations. The information presented provides a statistical evidence for the new proposed model for the near wall vortex distortion.