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A new k- ϵ model is introduced that is consistent with Monin-Obukhov similarity theory (MOST). The proposed k- ϵ model is compared with another k- ϵ model that was developed in an attempt to maintain inlet profiles compatible with MOST. It is shown that the previous k- ϵ model is not consistent with MOST for unstable conditions, while the proposed k- ϵ model can maintain MOST inlet profiles over distances of 50km. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We present a methodology to process wind turbine wake simulations, which are closely related to the nature of wake observations and the processing of these to generate the so-called wake cases. The method involves averaging a large number of wake simulations over a range of wind directions and partly accounts for the uncertainty in the wind direction assuming that the same follows a Gaussian distribution. Simulations of the single and double wake measurements at the Sexbierum onshore wind farm are performed using a fast engineering wind farm wake model based on the Jensen wake model, a linearized computational fluid dynamics wake model by Fuga and a nonlinear computational fluid dynamics wake model that solves the Reynolds-averaged Navier-Stokes equations with a modified k- ε turbulence model. The best agreement between models and measurements is found using the Jensen-based wake model with the suggested post-processing. We show that the wake decay coefficient of the Jensen wake model must be decreased from the commonly used onshore value of 0.075 to 0.038, when applied to the Sexbierum cases, as wake decay is related to the height, roughness and atmospheric stability and, thus, to turbulence intensity. Based on surface layer relations and assumptions between turbulence intensity and atmospheric stability, we find that at Sexbierum, the atmosphere was probably close to stable, although the stability was not observed. We support these assumptions using detailed meteorological observations from the Høvsøre site in Denmark, which is topographically similar to the Sexbierum region. © 2015 The Authors. Wind Energy published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

The newly developed k- ε- f P eddy viscosity model is applied to double wind turbine wake configurations in a neutral atmospheric boundary layer, using a Reynolds-Averaged Navier-Stokes solver. The wind turbines are represented by actuator disks. A proposed variable actuator disk force method is employed to estimate the power production of the interacting wind turbines, and the results are compared with two existing methods: a method based on tabulated airfoil data and a method based on the axial induction from 1D momentum theory. The proposed method calculates the correct power, while the other two methods overpredict it. The results of the k- ε- f P eddy viscosity model are also compared with the original k- ε eddy viscosity model and large-eddy simulations. Compared to the large-eddy simulations-predicted velocity and power deficits, the k- ε- f P is superior to the original k- ε model. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The recently developed k- ϵ- f P eddy-viscosity model is applied to one on-shore and two off-shore wind farms. The results are compared with power measurements and results of the standard k- ϵ eddy-viscosity model. In addition, the wind direction uncertainty of the measurements is used to correct the model results with a Gaussian filter. The standard k- ϵ eddy-viscosity model underpredicts the power deficit of the first downstream wind turbines, whereas the k- ϵ- f P eddy-viscosity model shows a good agreement with the measurements. However, the difference in the power deficit predicted by the turbulence models becomes smaller for wind turbines that are located further downstream. Moreover, the difference between the capability of the turbulence models to estimate the wind farm efficiency reduces with increasing wind farm size and wind turbine spacing. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An improved k- ϵ turbulence model is developed and applied to a single wind turbine wake in a neutral atmospheric boundary layer using a Reynolds averaged Navier-Stokes solver. The proposed model includes a flow-dependent C μ that is sensitive to high velocity gradients, e.g., at the edge of a wind turbine wake. The modified k- ϵ model is compared with the original k- ϵ eddy viscosity model, Large-Eddy Simulations and field measurements using eight test cases. The comparison shows that the velocity wake deficits, predicted by the proposed model are much closer to the ones calculated by the Large-Eddy Simulation and those observed in the measurements, than predicted by the original k- ϵ model. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]