A Field Validation Study of Mass-conserving and 3D Linear Wind Modelling at Blackford Hill, Edinburgh

Abstract

Assessments of the effect of terrain roughness on the flow of wind are essential in planning for civil engineering works, wildfire fighting, aviation, forecasting and in the energy transition, for which computational fluid dynamics derived diagnostic, and linear fluid flow models have been developed. An assessment of the turbulent wind flow over an isolated hill of high surface roughness (Blackford Hill, Edinburgh) has been conducted and a comparison between field anemometry and linear fluid flow, as well as outputs from the U.S. Department of Agriculture Forest Service's mass-conserving WindNinja model, has been made. The wider area around Blackford Hill presents a surface of high roughness, representative of a semi-urban environment and forming an ideal location to test model specificities and performance in varied prevailing wind conditions. Correlation of the net wind speed, as it is perturbed by topography relative to wind speed in the surrounding terrain, between measurements and both models is generally poor, owing to short averaging times, as well as model and methodological limitations in the case of this experiment. Both WindNinja and linear model outputs present greater correlation with field measurements for westerly wind profiles than easterly. Wind direction at the summit as it is perturbed by topography is generally better predicted by both methods with little difference from measured prevailing wind direction on respective days of measurements. Modelling of flow in upwind profiles and at the crest of the hill for both methods is generally more robust, though some significance for linear model predictions in the lee has been demonstrated for certain wind directions.