Jonathon Sumner

Influence of Atmospheric Stability on Wind Turbine Power Performance Curves

The impact of atmospheric stability on vertical wind profiles is reviewed and the implications for power performance testing and site evaluation are investigated. Velocity, temperature, and turbulence intensity profiles are generated using the model presented by Sumner and Masson. This technique couples Monin-Obukhov similarity theory with an algebraic turbulence equation derived from the k-e turbulence model to resolve atmospheric parameters u*, L, T*, and Zo. The resulting system of nonlinear equations is solved with a Newton-Raphson algorithm. The disk-averaged wind speed u disk is then evaluated by numerically integrating the resulting velocity profile over the swept area of the rotor. Power performance and annual energy production (AEP) calculations for a Vestas Windane-34 turbine from a wind farm in Delabole, England, are carried out using both disk-averaged and hub height wind speeds. Although the power curves generated with each wind speed definition show only slight differences, there is an appreciable impact on the measured maximum turbine efficiency. Furthermore, when the Weibull parameters for the site are recalculated using u disk, the AEP prediction using the modified parameters falls by nearly 5% compared to current methods. The IEC assumption that the hub height wind speed can be considered representative tends to underestimate maximum turbine efficiency. When this assumption is further applied to energy predictions, it appears that the tendency is to overestimate the site potential.

Evaluation of RANS/actuator disk modelling of wind turbine wake flow using wind tunnel measurements

Wake modelling plays a central role in wind farm planning through the evaluation of losses, the prediction of the energy yield, and the estimation of turbine loads. These models must be reasonably accurate – to minimise financial risk – and yet economical so that many configurations can be tested within reasonable time. While many such models have been proposed, an especially attractive approach is based on the solution of the Reynolds-averaged Navier-Stokes equations with two-equation turbulence closure and an actuator disk representation of the rotor. The validity of this approach and its inherent limitations however remain to be fully understood. To this end, detailed wind tunnel measurements in the wake of a porous disk (with similar aerodynamic properties as a turbine rotor) immersed in a uniform flow are compared with the predictions of several closures. Agreement with measurements is found to be excellent for all models. This unexpected result seems to derive from a fundamental difference in the tu...

The Apsley and Castro Limited-Length-Scale \({{k-\varepsilon}}\) Model Revisited for Improved Performance in the Atmospheric Surface Layer

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A Closer Look at Second-Moment Closure for Wind Farm Analysis

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k − ε simulations of the neutral atmospheric boundary layer: analysis and correction of discretization errors on practical grids

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Prediction of wake effects on wind farm power production using a RANS approach. Part II. Offshore: Case studies from the UPWIND project

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