Articles | Volume 1, issue 2
Research article
14 Jul 2016
Research article |  | 14 Jul 2016

The fence experiment – full-scale lidar-based shelter observations

Alfredo Peña, Andreas Bechmann, Davide Conti, and Nikolas Angelou

Abstract. We present shelter measurements of a fence from a field experiment in Denmark. The measurements were performed with three lidars scanning on a vertical plane downwind of the fence. Inflow conditions are based on sonic anemometer observations of a nearby mast. For fence-undisturbed conditions, the lidars' measurements agree well with those from the sonic anemometers and, at the mast position, the average inflow conditions are well described by the logarithmic profile. Seven cases are defined based on the relative wind direction to the fence, the fence porosity, and the inflow conditions. The larger the relative direction, the lower the effect of the shelter. For the case with the largest relative directions, no sheltering effect is observed in the far wake (distances ⪆ 6 fence heights downwind of the fence). When comparing a near-neutral to a stable case, a stronger shelter effect is noticed. The shelter is highest below  ≈ 1.46 fence heights and can sometimes be observed at all downwind positions (up to 11 fence heights downwind). Below the fence height, the porous fence has a lower impact on the flow close to the fence compared to the solid fence. Velocity profiles in the far wake converge onto each other using the self-preserving forms from two-dimensional wake analysis.

Short summary
We have developed flow models from different complexities. Unfortunately, high quality and reliable wind observations affected by obstacles are rare and so we have few means to evaluate our models. We have therefore performed a campaign in which we measured the effect of a fence on the atmosphere using laser-based instruments. The effect can still be noticed as far as 11 fence heights. A wake theory seems to predict the obstacle effect when we are looking at distances beyond 6 fence heights.