Prediction of the performance reduction on the Darrieus vertical-axis tidal-current turbine due to surface roughness when operating in tropical seawater environments

초록

Darrieus Vertical Axis Turbines (D-VATs) are well suited for Indonesia's low-velocity tidal currents but are highly susceptible to marine biofouling-induced surface roughness under tropical conditions, leading to increased drag and degraded hydrodynamic performance. The impact of surface roughness on D-VAT performance is systematically investigated through full-scale URANS CFD simulations with experimentally derived rough-wall boundary conditions, addressing the roughness scaling limitations commonly associated with model-scale turbine studies. Eight roughness scenarios were evaluated over Tip Speed Ratios (TSRs) ranging from 1.2 to 2.8. The results indicate a linear relationship between increasing roughness height and reductions in the power coefficient (Cp). At TSR 1.2, Cp decreased by approximately 2% under mild surface roughness conditions (≈0.30 to 0.29) and by up to 39.28% under severe roughness conditions (≈0.30 to 0.18) relative to a smooth surface. Under the most severe roughness condition, the mechanical power (Pmech) decreased by up to 62% at TSR 2.8 compared to the smooth-surface condition. Increasing TSR intensified the performance degradation in both Cp and Pmech across all roughness scenarios. Flow contour showed that severe surface roughness promotes widespread turbulent flow and flow separation, weakening pressure loading and torque generation around the turbine blade. The cumulative energy generation further demonstrated that prolonged operation under severe roughness conditions substantially reduces the long-term energy conversion capability of the D-VAT system in tropical marine environments. © 2026 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC license. http://creativecommons.org/licenses/by-nc/4.0/

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