Meandering of turbine wake flow induced by atmospheric eddies

A novel algorithm is developed to calculate the nonlinear optimal boundary perturbations in three-dimensional incompressible flow. An optimal step length in the optimisation loop is calculated without any extra calls of the governing PDEs. This algorithm is further applied to compute the optimal inflow eddies that induce wake oscillations in flow around a turbine blade, which is modelled as an actuator disc. Over the parameters considered, the most energetic inflow perturbation occurs at frequency ω = 1 ∼ 2 and is mainly in the form of an azimuthal Fourier wave with wavenumber 1. The development of the inflow perturbation induces significant oscillations of the wake flow. At 10 turbine radii downstream of the disc, the centre velocity oscillates at a magnitude over half of the free-stream velocity, when the maximum inflow noise is 6% of the free-stream wind speed.