A wind tunnel simulation of the turbulence fields behind upright porous wind fences

The turbulence field of airflow behind a porous fence has significant impacts on the fence's shelter efficiency. We used particle image velocimetry to obtain detailed velocity measurements behind two-dimensional porous fence models in a wind tunnel simulation, and analyzed the turbulence fields revealed by these measurements. We tested fence models with 11 porosities: 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9, and analyzed seven typical fences. The reduction of mean streamwise velocity behind all fences increased with decreasing fence porosity, but created a corresponding increase in the mean vertical velocity component turbulence. We used vorticity, turbulence intensity, Reynolds stress, and turbulent kinetic energy to characterize the turbulence fields. Of these parameters, only the turbulence intensity is found to be directly related to the shelter efficiency of fences in terms of sediment transport on the surface because the magnitudes of the other parameters nearest the surface are insignificant. Vorticity causes loss of wind energy and tends to lift sediment particles carried by the wind passing over the fences to higher levels. It is found that flow reattachment behind fences is related to the high turbulence intensity nearest to the surface and high Reynolds stress and turbulent kinetic energy in the layer right above. The optimal fence porosity we proposed in a previous study is found to be the critical porosity above which turbulence intensity and vertical velocity component are greatly reduced. Further research is required to make a comprehensive assessment of shelter efficiency of wind fences, taking account of the wind reduction and turbulence fields.

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