Wall Roughness in Turbulent Flow

Here are a couple of movies of high-fidelity simulations of turbulent boundary layers over rough surfaces and perfectly flat surfaces. The conditions were chosen to match experiments carried out at the University of Tennessee Space Institute. The freestream Mach number was about M = 2.0 and the momentum thickness Reynolds number (based on wall viscosity) was about Re_θi = 15000.

The work has been documented in detail in:

• J. J. Gaskins, J. Poggie, and G. Blaisdell, "A Preliminary Study of Roughness Effects on a Compressible Turbulent Boundary Layer," AIAA Paper 2021-1445, January 2021.
• J. J. Gaskins, "The Effect of Near Wall Disturbances on a Compressible Turbulent Boundary Layer," M.S., Purdue University, August 2021.
• J. J. Gaskins, J. Poggie, and G. A. Blaisdell, "Simulation of a High Reynolds Number Compressible Turbulent Boundary Layer Developing in the Presence of a Sinusoidal Plane," AIAA Paper 2022-3251 June 2022.

A movie from the baseline flat wall case is shown below. The orange contours represent skin friction magnitude on the flat wall. The greyscale contours represent density in a side plane and an end plane. At this relatively high Reynolds number (for a computation) we see the large separation of scales between the large-scale bulges in the outer part of the boundary layer and the footprints of the near-wall streaks at the wall.

For comparison, a rough-wall case is shown below. (Strictly speaking, this is a wavy wall case.) The corrugated pattern of the wavy surface of the wall is apparent. Close observation of the skin friction patterns shows a tendency of the streaks to wind their way through the valleys in the wall surface pattern.