A Simple Temporal and Spatial Analysis of Flow in Complex Terrain in the Context of Wind Energy Modelling

A simple temporal and spatial analysisis done on wind speed and direction data from a number ofmeteorological towers separated by distances between roughly 1 and 100 kilometres. The analysis is done in the context of expected model error in wind energy calculations. The study first uses single point statistics to show the evolution of mean values with time. It is shown that strong seasonal signals are present and that stable means are achieved only after averaging periods of a year or more. The study then uses discrete Fourier transforms to show that significant amounts of spectral energy reside in modes with periods of a few days to less than a day. Frequency dependent cross correlation values are then derived and used to show how correlation between towers diminishes with increasing frequency. The mechanism responsible for this diminished correlation is shown through the comparison of cross-correlation phase as a function of frequency and its relationship to distance between towers. Error in wind energy estimates are shown to be strongly related to correlation and therefore distance over which the prediction is made. In summary, much of the inaccuracy in modelling flow in the context of wind energy calculations is due to a lack of scale separation between the deterministic part of the flow, which is well modelled, and that part of the flow that is stochastic at the length and time scales modelled.

[1]  William H. Press,et al.  Numerical Recipes in FORTRAN - The Art of Scientific Computing, 2nd Edition , 1987 .

[2]  Peter A. Taylor,et al.  Development of a non-linear mixed spectral finite difference model for turbulent boundary-layer flow over topography , 1994 .

[3]  Peter A. Taylor,et al.  A non-linear extension of the mixed spectral finite difference model for neutrally stratified turbulent flow over topography , 1992 .

[4]  P. Taylor,et al.  The Askervein Hill project: Overview and background data , 1987 .

[5]  Erik Lundtang Petersen,et al.  The European Wind Atlas , 1985 .

[6]  R. Stull.  Review of non-local mixing in turbulent atmospheres: Transilient turbulence theory , 1993 .

[7]  F. Hewer.  Non-Linear Numerical Model Predictions of Flow Over an Isolated Hill of Moderate Slope , 1998 .

[8]  E. F. Bradley,et al.  Boundary-layer flow over low hills , 1987 .

[9]  P. Taylor,et al.  The Kettles Hill Project: Field observations, wind-tunnel simulations and numerical model predictions for flow over a low hill , 1988 .

[10]  N. Mortensen,et al.  Exploring the limits of WAsP the wind atlas analysis and application program , 1996 .

[11]  Peter A. Taylor,et al.  A Mixed Spectral Finite-Difference 3D Model of Neutral Planetary Boundary-Layer Flow over Topography. , 1995 .

[12]  I. Troen,et al.  A simple model of the atmospheric boundary layer; sensitivity to surface evaporation , 1986 .

[13]  K. Ayotte,et al.  The impact of turbulence closure schemes on predictions of the Mixed Spectral Finite-Difference model for flow over topography , 1994 .

[14]  Nigel Wood,et al.  Wind Flow Over Complex Terrain: A Historical Perspective and the Prospect for Large-Eddy Modelling , 2000, Boundary-Layer Meteorology.

[15]  N. Wood,et al.  The Pressure force induced by neutral, turbulent flow over hills , 1993 .

[16]  J. Walmsley,et al.  A method of correlating wind data between two stations with application to the Alberta oil sands , 1978 .

[17]  Peter A. Taylor,et al.  A mixed spectral finite-difference model for neutrally stratified boundary-layer flow over roughness changes and topography , 1987 .

[18]  J. Hunt,et al.  Turbulent shear flows over low hills , 1988 .