This work addresses the problem of developing control algorithms for the control of the aerodynamic lift of wind turbine blades using air injection, taking into account disturbances caused by turbulent perturbations. For this, a test bench is used where the lift of a 2D blade section in a wind tunnel can be controlled by a set of micro-jets close to the trailing edge. Through a continuous, local identification of the lift variations a model-free control that does not need any prior knowledge of the system is proposed. It allows the control of the flow of the micro-jets and stabilizes the lift around a tracking reference. The ability of the proposed control algorithm to track the lift reference when subjected to external perturbations, i.e., gusts, is discussed. In particular, this work demonstrates that the lift can be set to particular values using the proposed control strategy, and can be re-stabilized to pre-gust lift conditions. Experimental results illustrate globally the feasibility of such a control.
Wind turbines operate in the turbulent atmospheric boundary layer and can be additionally exposed to the wakes of upstream wind turbines. Hence the inflow encountered by wind turbine rotor blades is turbulent. One way to gain more knowledge on the impact of the turbulence on the airfoil aerodynamics is by studying a 2d airfoil section of a real wind turbine blade against inflows of various turbulence intensities and Reynolds numbers. Therefore, for the purpose of this paper, experiments were performed and aerodynamic coefficients were calculated for chord based Reynolds numbers between 1.3 × 105 and 3 × 105 and angles of attack between -10° and 24° for inflows of three different averaged turbulence intensities, 0.3%, 3% and 5.5%. Results were compared with the already available result of measurements done at a higher chord based Reynolds number of 4.7×106 for the same airfoil type. The results show that, for a given Reynolds number, an increase in turbulence intensity suppresses the flow separation. It was also found that an increase in the turbulence intensity of the inflow does reduce the dependence of aerodynamic coefficients on the Reynolds number. The Comparison between experimental results for lower chord-based Reynolds numbers and high chord-based Reynolds numbers shows differences which implies that an increase of the turbulence intensity is not enough to bypass the low Reynolds number effect completely.
Abstract. Wind energy systems, such as horizontal-axis wind turbines and vertical-axis wind turbines, operate within the turbulent atmospheric boundary layer, where turbulence significantly impacts their efficiency. Therefore, it is crucial to investigate the impact of turbulent inflow on the aerodynamic performance at the rotor blade scale. As field investigations are challenging, in this work, we present a framework where we combine wind tunnel measurements in turbulent flow with a digital twin of the experimental setup. For this, first, the decay of the turbulent inflow needs to be described and simulated correctly. Here, we use Reynolds-Averaged Navier-Stokes (RANS) simulations with k −ω turbulence models, where a suitable turbulence length scale is required as an inlet boundary condition. While the integral length scale is often chosen without a theoretical basis, this study derives that the Taylor micro-scale is the correct choice for simulating regular grid generated turbulence: the temporal decay of turbulent kinetic energy (TKE) is shown to depend on the initial value of the Taylor micro-scale by solving the differential equations given by Speziale and Bernard in 1992. Further, the spatial decay of TKE and its dependence on the Taylor micro-scale at the inlet boundary are derived. With this theoretical understanding, RANS simulations with k − ω turbulence models are conducted using the Taylor micro-scale and the TKE obtained from grid experiments as the inlet boundary condition. Second, the results are validated with excellent agreement with the TKE evolution downstream of a grid obtained through hot-wire measurements in the wind tunnel. Third, the study further introduces an airfoil in both the experimental and the numerical setting where 3d simulations are performed. A very good match between force coefficients, obtained in experiments and in the digital twin, is found. In conclusion, this study demonstrates that the Taylor micro-scale is the appropriate turbulence length scale to be used as the boundary condition and initial condition to simulate the evolution of TKE for regular grid generated turbulent flows. Additionally, the digital twin of the wind tunnel can accurately replicate the force coefficients obtained in the physical wind tunnel.
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