Model for propagation speed in turbulent channel flows

Area of Science:

• Fluid dynamics
• Turbulence research
• Computational physics

Background:

• Understanding turbulent flow dynamics is crucial for various engineering applications.
• The behavior of velocity fluctuations in turbulent flows, especially at varying Mach numbers, requires detailed investigation.
• Previous studies suggested coherent vortex structures influence near-wall propagation, but lacked quantitative validation.

Purpose of the Study:

• To calculate and analyze the propagation speed (Vc) of streamwise velocity fluctuations (u') in turbulent channel flows.
• To develop and validate a quantitative model for predicting Vc across a range of Mach numbers (M).
• To confirm the role of coherent vortex structures and the Velocity-Vorticity Correlation Structure (VVCS) in near-wall propagation.

Main Methods:

• Direct Numerical Simulation (DNS) was employed to generate data for turbulent channel flows.
• Analysis focused on four distinct Mach numbers: M=0, 0.8, 2.0, and 3.0.
• A novel statistical structure, the Velocity-Vorticity Correlation Structure (VVCS), was defined and utilized for modeling.

Main Results:

• Profiles of propagation speed (Vc) exhibited remarkable similarity across all investigated Mach numbers.
• The developed VVCS-based quantitative models showed good agreement with DNS-measured propagation velocities.
• The findings validated the concept of VVCS and confirmed advection by coherent vortex structures for near-wall propagation.

Conclusions:

• The propagation speed of velocity fluctuations in turbulent channel flows is largely independent of Mach number.
• The Velocity-Vorticity Correlation Structure (VVCS) provides a robust framework for modeling turbulent flow propagation.
• The study validates the significant contribution of coherent vortex structures to near-wall turbulent transport.