The Kettles Hill Project: Field observations, wind-tunnel simulations and numerical model predictions for flow over a low hill

Abstract

Field observations of the influence of topography on steady, neutrally-stratified boundary-layer flow were carried out in February 1981 and March 1984 on Kettles Hill near Pincher Creek, Alberta, Canada. The primary measurements were of wind speed at 3,6, and 10 m levels at stations in linear arrays along and across the major axis of this gentle, 1 km long and 100 m high, elliptical hill. Wind profile measurements up to heights of 200 m were made with TALA kites and tethersondes on the hilltop and at a reference site located about 3.7 km west of the hilltop. In addition, AIRsondes were flown and tracked from the reference site to provide additional data. The field observations provided the basic data for a comparison with wind-tunnel and numerical model simulations of the same flow. The wind-tunnel investigation was carried out in the Atmospheric Environment Service Boundary-Layer Wind Tunnel while the numerical model used was MS3DJH. For ‘horizontal’ profiles of normalized mean wind speed at given heights above the prototype terrain, model results agree reasonably well with the field data. The wind-tunnel predictions are slightly high in most cases. For vertical profiles of wind speed up to 200 m above the hilltop, the numerical and wind-tunnel values are higher than were observed. The sensitivity of the normalized wind speed at the hilltop to deviations from non-logarithmic upwind profiles is demonstrated with data from the March 1984 experiment. A comparison of prototype with numerical-model mean-wind-direction perturbations at the 10 m level shows reasonable agreement except near the summit of the hill.