On the laminar–turbulent transition mechanism on megawatt wind turbine blades operating in atmospheric flow

Abstract

Abstract. Among a few field experiments on wind turbines for analyzing laminar–turbulent boundary layer transition, the results obtained from the DAN-AERO and aerodynamic glove projects provide significant findings. The effect of inflow turbulence on boundary layer transition and the possible transition mechanisms on wind turbine blades are discussed and compared to CFD (computational fluid dynamics) simulations of increasing fidelity (Reynolds-averaged Navier–Stokes, RANS; unsteady Reynolds-averaged Navier–Stokes, URANS; and large-eddy simulations, LESs). From the experiments, it is found that the transition scenario changes even over a single revolution with bypass transition taking place under the influence of enhanced upstream turbulence, for example, such as that from wakes, while natural transition is observed in other instances under relatively low inflow turbulence conditions. This change from bypass to natural transition takes place at azimuthal angles directly outside the influence of the wake indicating a quick boundary layer recovery. The importance of a suitable choice of the amplification factor to be used within the eN method of transition detection is evident from both the RANS and URANS simulations. The URANS simulations which simultaneously check for natural and bypass transition match very well with the experiment. The LES predictions with anisotropic inflow turbulence show the shear-sheltering effect and a good agreement between the power spectral density plots from the experiment and simulation is found in case of bypass transition. A condition to easily distinguish the region of transition to turbulence based on the Reynolds shear stress is also observed. Overall, useful insights into the flow phenomena are obtained and a remarkably consistent set of conclusions can be drawn.

Model wind turbine performance in turbulent–non-turbulent boundary layer flow

“…Wind turbines are continuously growing and reaching unprecedented blade tip heights [1]. At these heights, rotor blades are sweeping through different flow regions characterized by strong velocity and turbulence gradients [2]. A recent investigation demonstrated the presence of the laminar-turbulent transition region (turbulent-non-turbulent interface (TNTI)) even at low heights (< 100 m) within the rotor area of wind turbines [3].…”

The fractal turbulent/non-turbulent interface in the atmosphere

“…Wind fluctuations on short time scales are known to induce fluctuations in the power output of wind turbines (Milan et al, 2013). Further, also a varying turbulence intensity (TI) of the inflow over the rotor is significantly influencing the turbine operation (Lobo et al, 2023).…”