Performance analysis of novel wavy-wall-based flow control method for wind turbine blade

In this paper, the experimental study in flat-plate turbulent boundary layer (TBL) under various Reynolds number and adverse pressure gradient (APG) conditions was performed downstream of the wavy wall, which proved to be effective in delaying flow separation in Dróżdż et al. (2021). Three Reynolds numbers that reproduce the effect of slow changes in wind conditions on a large-scale pitch adjusted wind turbine (range of wind speed: $5-40\mathrm{m/s}$) and three pressure gradient evolutions that reproduce sudden changes in the relative inflow wind angle resulting from a rotation cycle and/or a blade torsional deflection cycle were analysed. The effect of Reynolds number was found to have a weak dependence on the performance of the method, since there was only about a 2% reduction in performance in the Reynolds number range studied, compared to the maximum efficiency of 15.5%. In contrast, for the maximum change in the pressure gradient, a decrease of 8.8% in the efficiency of the flow control method was reported. Assuming that a strong change in the pressure distribution occurs for at most a quarter of the blade deflection cycle, the rotor efficiency decreases by no more than 3.5%. Thus, the total efficiency of the method is not less than 10%. The results show that the chosen corrugation geometry works well under both nominal and off-design wind turbine rotor conditions. It was also shown that the method’s efficiency in postponing flow separation can be evaluated by increasing or maintaining total momentum, quantified by the changes in momentum-loss thickness due to wavy wall.