Numerical Study of Axial Turbulent Flow Over Long Cylinders.

摘要

Convex transverse curvature effects in wall bounded turbulent flows are significant if the boundary layer thickness is large compared to the radius of curvature. The curvature affects the inner part of the flow if a+, the cylinder radius in wall units, is small. This flow regime is common in sonar devices towed by long cables. Two direct numerical simulations of transversely curved flows were performed and statistical and structural data were extracted from the computed flow fields. The effects of the transverse curvature were identified by comparing the present results with those of the plane channel simulation, performed at a similar Reynolds number. As expected, the transversely curved turbulent flow exhibits many features common to the planar flows: near-wall low speed streaks, near-wall inclined shear layers, near-wall streamwise vortices, Reynolds shear stress dominated by second and fourth quadrant events, etc. As the curvature increases, the skin friction increases, the slope of the logarithmic region decreases and turbulence intensities are reduced. Several turbulence statistics are found to scale with a curvature dependent velocity scale derived from the mean momentum equation. Near the wall, the flow is more anisotropic than in the plane channel with a larger percentage of the turbulent kinetic energy resulting from the streamwise velocity fluctuations. Near-wall streamwise vortices are the strongest sources of pressure fluctuations. As the curvature increases, regions of strong normal vorticity develop near the wall.