A new rough wall layer modeling for turbulent flows using the Brinkman equation

A new flow physics-based modeling of surface roughness effects is developed for the Reynolds averaged Navier-Stokes equations numerical calculations of high-Reynolds-number turbulent flows over a wide range of rough surfaces. In light of the geometric and the dynamic similarities between the porous medium flow and the surface roughness flow, it is proposed herein to use the Brinkman equation to model the averaged flow in the surface roughness layer of the turbulent boundary layer flow. The averaged model equations for the mean flows are derived and turbulence transport equations are developed based on existing smooth wall turbulence closures. The roughness-related model parameters are also introduced.;In the proposed approach, the fluid dynamics of the averaged flow in the near-wall rough layer is modeled by using the Brinkman equation. The porosity can be calculated based on the volumetric characteristics of the roughness and the permeability is modeled. The Reynolds averaged Navier-Stokes equations are solved numerically in the outer free flow region, which is above the near-wall rough layer, while a low-Reynolds-number k - epsilon model and a second-order Reynolds stress model are employed in all regions. The interface conditions are applied to enforce the continuity of velocity, pressure, and turbulence properties, and the stress jump at the interface between the near-wall rough layer and the free flow region.;The computational results, including the skin friction coefficient, the log-law mean velocity, the roughness function, the turbulent kinetic energy, and the Reynolds stresses, are presented. The results show that the new rough wall layer modeling approach predicts well the skin friction coefficient, the log-law mean velocity, the roughness function, and the Reynolds shear stress. The results indicate that the developed rough wall layer modeling approach improves the current predictive capability of the roughness effects, and is applicable to a wider range of surface roughness.