Resolvent analysis for predicting energetic structures in the far wake of a wind turbine

Abstract: A thorough understanding of the energetic flow structures that form in the far wake of a wind turbine is essential for accurate turbine wake modeling and wind farm performance estimation. We use resolvent analysis to explore such flow structures for a turbine operating in a neutral atmospheric boundary layer and validate our results against data-driven modes extracted through spectral proper orthogonal decomposition. Our results confirm that convective instabilities play a dominant role in generating turbulent kinetic energy (TKE) in the far wake. Additionally, we find evidence of the non-modal Orr mechanism contributing to TKE generation, particularly at low Strouhal numbers. The resolvent analysis method requires only the mean wake velocity and eddy viscosity profiles as inputs but can capture the energetic modes and TKE spectra in the far wake. In this specific application, the resolvent analysis method approximates the wake to be axisymmetric, which suggests that it can be paired with engineering wake models. Overall this study demonstrates the use of resolvent analysis as a viable tool for estimating TKE and for uncovering the mechanism of TKE generation.