Sand erosion technique applied to wind resource assessment

One of the major challenges of the wind energy sector is to accurately predict the wind potential. This task is especially difficult in mountainous terrains where the topography can imply complex relief-induced flows. Wind tunnel testing is one of the possibilities to simulate and predict the wind for wind turbine micro-siting. Most advanced quantitative measurement techniques can be used in the wind tunnel, however, measuring the whole terrain to find the highest wind potential zones is very time-consuming. This paper proposes to use a very simple, quick and cheap technique to detect and evaluate the high wind speed areas over an entire model. Commonly used for pedestrian wind comfort assessment, the sand erosion technique is here applied to wind resource assessment. The technique can provide valuable qualitative information but can also give an order of magnitude of the local speed-up. It is first applied to a backward facing step flow and then on a mountainous terrain. An amplification factor and the fractional speed-up ratio (FSR) can be calculated over the entire mountain. For high speed positions results extracted from sand erosion appears to be comparable the one calculated by particle image velocimetry. The technique is repeatable, able to perform a detection of the high speed area, and capable of giving an estimation of the amplitude of the wind. The technique allows to restrict the use of quantitative measurements to the most interesting areas.

► Sand erosion to detect high wind locations and limit the use of expensive techniques. ► First test case: backward-facing step, comparison with PIV. ► Second test case: mountainous terrain, repeatability study and comparison with PIV. ► The technique is able to provide qualitative and to estimates quantitative data. ► Fast, easy and cheap for a first view of the speed-up before detailed measurements.