Numerical modeling of turbulence above offshore helideck – Comparison of different turbulence models

The turbulent flow over an offshore oil-rig helideck has been simulated by a commercial engineering CFD code, Star-CCM+, with nine different turbulence models: two Reynolds-stress transport equation (RSE) models, six k–εk–ε models and one k–ωk–ω model. Simulations by the same code and models were compared to experimental data for simpler test cases, including flows over a backward-facing step and a surface-mounted cube. The primary aim was to compare RSE models to two-equation models on the background of a new industry standard for helicopter operation with requirements on the vertical velocity variance over the helideck. It was found that RSE models do not outperform two-equation models for separated flows and wakes. The RSE models seem to underpredict the turbulence energy more than the two-equation models and hence, also the vertical velocity variance. Among the two-equation models, the realizable k–εk–ε model and Menter׳s k–ωk–ω model performed better than the standard k–εk–ε model, while a cubic k–εk–ε model predicted unphysical, negative normal Reynolds stresses. Attempts on adjusting the coefficients of the k–εk–ε model, as promoted by some authors, worked fine for undisturbed atmospheric flow but quite poor for more complex flows.