Effects of form-induced velocity in rough-wall turbulent channel flows

Abstract

Wall roughness induces form-induced (or dispersive) velocity and pressure perturbations inside the roughness sublayer of a wall-bounded turbulent flow. This work discusses the role played by the form-induced velocity in influencing turbulence statistics and structure, using existing direct numerical simulation data of transient half channels in response to an impulse acceleration (Mangavelli et al. Effects of surface roughness topography in transient channel flows. J Turbul 2021;22:434–460). Focuses are given to (i) reshaping of turbulent coherent motions by the rate-of-strain of the mean velocity, and (ii) contributions of different velocity sources to turbulent pressure fluctuations. Half-channel flows in both fully-developed and non-equilibrium, transient states are discussed. Results show that form-induced velocity gradients not only form an important source of turbulent pressure in an equilibrium flow, but also lead to turbulence production and potentially direct structural change of turbulent eddies in a non-equilibrium flow under acceleration.

Keywords:

• Direct numerical simulation
• turbulent boundary layers

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors gratefully acknowledge the financial support of the Office of Naval Research [award number N00014-17-1-2102].