The effects of a bottom gap and non-uniform porosity in a wind fence on the surface pressure of a triangular prism located behind the fence

The effects on the surface pressure of a modeled coal stockpile caused by the introduction of a gap near the ground and non-uniform porosity in a wind fence were investigated experimentally. The porous fence and coal stockpile models were embedded in a simulated neutrally stable atmospheric boundary layer typically found over a city suburb. Various porosity combinations in the upper and lower fence halves were tested. The fence and coal stockpile models were both 40 mm high; the Reynolds number based on the model height (H) was Re=3.9 × 10⁴. The mean pressure on the coal pile surface was found to increase with the size of the gap near the ground for a fence of porosity ε=40%. Local minimum values of the pressure fluctuations were located on the windward surface for a gap (G) of G/H = 0.125. The mean pressure and pressure fluctuations on the model surface were strongly affected by the fence porosity ε. When different values of porosity were used for the upper and lower halves of the fence, the mean and rms pressure fluctuations increased. A fence with different values of porosity for the top and bottom halves provided a smaller shelter effect than a fence with uniform porosity, ε = 40%.