A Numerical Approach for Modeling Roughness for Marine Applications

A roughness wall model based on the equivalent sandgrain roughness approach that accounts for the log-law solution for turbulent boundary layer over fully rough surfaces is implemented into a viscous flow solver called NavyFOAM. The rough wall model is implemented as a wall function and is used in conjunction with the k-ω turbulence model. The roughness model is validated against experiments conducted on rough plates in a water tunnel and towed in a channel. Two sets of simulations, single-phase Reynolds-Averaged Navier-Stokes (RANS) and two-phase unsteady RANS were conducted to validate the current roughness model. Current results show good agreement with the roughness functions (ΔU⁺) and is within 1.5% of the experimental results. The overall frictional resistance predicted for the rough plates towed in a water channel is within 2% of the experimentally obtained results. With these promising results, the aim is to develop a computational capability for predicting added hull resistance due to biofouling.