Numerical Analysis of Yawed Turbine Wake under Atmospheric Boundary Layer Flows (original) (raw)
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Turbine-wake interactions among wind turbine array significantly affect the efficiency of wind farms. Yaw angle control is one of the potential ways to increase the total power generation of wind plants, but the sensitivity of such control strategy to atmospheric stability is rarely studied. In the present work, large-eddy simulation of a two-turbine configuration under convective atmospheric boundary layer is performed, with different yaw angles for the front one, the effect of turbine induced forces on the flow field is modeled by actuator line. Emphasis is placed on wake characteristics and aerodynamic performance. Simulation results reveal that atmospheric stability has a considerable impact on the behavior of wind turbine, wake deflection on the horizontal hub height plane for yawed wind turbine is relatively small, compared with the result of the empirical wake model proposed for wind turbine operating in the neutral stratification, which is attributed to the higher ambient tu...
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This study introduces a numerical investigation on the impact of different inflow atmospheric conditions on the wind turbine wakes. The effects of the inflow turbulence intensity and wind speed under thermally-stratified atmospheric boundary layer (ABL) are presented and discussed. The steady state three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations are solved in the simulation, along with the Actuator Disk Method (ADM) for the turbine rotor modeling. A modified-model, namely El Kasmi model, is adopted for the turbulence modulation. Further, an additional source term is added to the turbulence equations, to artificially represent the buoyancy generated turbulence, without the need to solve the energy equation. It is found that, there is a considerable effect of the different atmospheric flow properties on the wake flow behavior. Particularly, as the turbulence intensity increases, the wake recovers faster and hence, the wake deficit decreases and the available wind power in the wake region increases. Further, the wake deficits values immediately downstream the turbine are higher for the lower inflow wind speeds.
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This paper analyses the effect of a mean shear similar to an atmospheric boundary layer on the wake of a wind turbine by means of Large Eddy Simulation. More specifically, a comparison is made between the wake in the presence of a smooth boundary layer and that in the absence of a boundary layer (i.e., an unconfined uniform incoming flow). The numerical simulations show that the presence of a smooth boundary layer lowers the power output, however, the rings of tip vortices in the presence of a power-law incoming flow are more stable than for a uniform incoming flow. More importantly, the length of the wake region for the case with the smooth boundary layer is about 12D, which is much shorter than for a uniform incoming flow (namely 20D). Strong downwash, observed at this distance in the presence of a smooth boundary layer, results in a higher velocity magnitude and lower turbulence in the far wake of the wind turbine when compared with a uniform flow. A mechanism explaining these observations is also proposed. This new knowledge may result in denser wind farms, compared with wind farms established on smoother surfaces.
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Correct prediction of the recovery of wind turbine wakes in terms of the wind velocity and turbulence downstream of the turbine is of paramount importance for the accurate simulations of turbine interactions, overall wind farm energy output and the impact to the facilities downstream of the wind farm. Conventional turbulence models often result in an unrealistic recovery of the wind velocity and turbulence downstream of the turbine. In this paper, a modified k turbulence model has been proposed together with conditions for achieving a zero streamwise gradient for all the fluid flow variables in neutral atmospheric flows. The new model has been implemented in the simulation of the wakes of two different wind turbines and the commonly used actuator disk model has been employed to represent the turbine rotors. The model has been tested for different wind speeds and turbulence levels. The comparison of the computational results shows good agreement with the available experimental data, in both near and far wake regions for all the modeled wind turbines. A zero streamwise gradient has been maintained in the far wake region in terms of both wind speed and turbulence quantities.