The propagation speed $V_c$ of the streamwise velocity fluctuations $u^{\prime }$ in turbulent channel flows is calculated using direct numerical simulation (DNS) data at four Mach numbers ($M=0$, $0.8$, $2.0$, and $3.0$). The profiles of $V_c$ are shown to display remarkable similarity at different $M$. Quantitative models are developed based on a statistical structure called Velocity-Vorticity Correlation Structure (VVCS), defined as the vorticity region most correlated to velocity fluctuations at a fixed location. Good agreement with DNS-measured propagation velocities is obtained throughout the channel and for all $M$. The result confirms earlier speculation that the near-wall propagation is due to an advection by coherent vortex structures, and validates the concept of the VVCS.

• Received 4 April 2012

DOI:https://doi.org/10.1103/PhysRevE.86.046307