The effect of pressure gradient and turbulence intensity on wind turbine wake and performance

Streamwise pressure gradients and turbulence intensity can affect wind turbine performance and wake characteristics. In this work, we investigate the combined effect of a constant pressure gradient and turbulence intensity on the performance and wake of a turbine via wind tunnel experiments. Five different pressure gradients are imposed using linear ramps, and three different surface characteristics are used to alter the turbulence intensity level. The power and thrust coefficients show high sensitivity to the pressure gradient, whereas limited sensitivity to the turbulence intensity is observed. On the other hand, power fluctuations are found to be dependent on the turbulence intensity but not on the pressure gradient. The wake velocity deficit depicts the typical behavior of a faster recovery under a higher turbulence intensity for a certain pressure gradient, where the velocity deficit increases for an adverse pressure gradient and decreases for a favorable one compared to zero pressure gradient for all turbulence intensities. The wake growth rate and near-wake length are characterized as functions of pressure gradient and turbulence intensity. It is, thereby, observed that an increase in turbulence intensity diminishes the effect of pressure gradient on the wake growth rate and near-wake length. Finally, two analytical models for wake velocity deficit under pressure gradient are compared against the experimental data.