A Numerical Study on Flow around Nonuniform Porous Fences

Abstract

The effects of a porous fence with a nonuniform porosity on flow fields are investigated numerically. First, an experiment with a non-uniform porous fence located in a wind tunnel is performed to obtain a reference data set. Then, a numerical model that utilizes the finite volume scheme with a weakly compressible-flow method to solve the continuity and momentum equations is developed. The numerical simulation is compared to experimental measurements for validation purposes. As a result, the numerical predictions show good agreements with the experimental data. Finally, the numerical investigations of the flow fields around porous fences with various combinations of upper and lower fence porosity are also presented. When the upper porosity is greater than the lower porosity, the Protection Index PI 0.1 , PI 0.3 and PI 0.5 , representing the adverse sheltering effect, decreases compared to that of the uniform porous fence. When the upper porosity is less than the lower porosity, the PI 0.5 increases and the variations of the PI 0.1 and PI 0.3 , depend on the upper porosity, compared to that of the uniform porous fence. The results show that the porous fence with the upper fence porosity ε U 0% and the lower fence porosity ε L 30% gives the best sheltering effect among the porous fences in this study.

The Concentrations and Reduction of Airborne Particulate Matter (PM10, PM2.5, PM1) at Shelterbelt Site in Beijing

“…The reason for this kind of phenomenon is that the spatial structure of forest belt affecting the microclimate would change the PM mass concentration inside the shelterbelt. In general, airflow through the forest belt can be divided into two parts: when lower air flow encounters the shelterbelt, owing to a blocking effect by the shelterbelt, part of the airflow moves directly through the shelterbelt gap; the friction between the airflow and the tree consumes more energy of the flow and causes the kinetic energy of the airflow to drop, which leads to the wind speed reducing [66][67][68][69]. The reduction in wind in the shelterbelt, not conducive to the spread of PM, which is prone to settlement, eventually leads to an increase in PM mass concentration.…”

Flow around porous barriers

“…x 11.2 Background ...........................................................................................297 11.3 Study Site and Experimental Needs .....................................................300 11.4 CRP Overview ......................................................................................304 11.5 CRP Implementation ............................................................................307 11.5.1 Components customization and experimental arrangement .......307 11.5.2 Experimental protocols ...............................................................308 11.6 CRP Sensitivity and Accuracy Analysis ...............................................310 11.6.1 Effect of the density and distribution of the ground control points .. ...................................................................................................311 11.6.2 Surface texture ............................................................................312 11.6.3 CRP mapping accuracy ..............................................................313 11.7 Tracking Snow Deposition during a Strom Event ................................315 11.8 Conclusions...........................................................................................317 CHAPTER 12 CONCLUSIONS AND FUTURE WORK ..............................................333 REFERENCES ................................................................................................................337 xi LIST OF TABLES Table 2.1 Protection Index (PI) values predicted by Huang et al (2012) representing areas under contours line u/u0=0.1, 0.3 and 0.5 behind a porous fence with nonuniform porosity (see also xii LIST OF FIGURES Figure 1.1 Flow including separation and reattachment zone around an obstacle or windbreak (Raine and Stevenson, 1977). Note that for high porosities, upwind and downwind recirculation regions may be absent.…”

“….................47 Figure 2.9 Mean streamwise velocity (u/U0) and vertical velocity (v/U0) profiles in the wake of a porous fence (P=38.5%) with varying hole diameters d=1.4mm, d=2.1mm and d=2.8mm. From Kim and Lee (2001), where U0 is the incoming flow velocity, H is the height of .12 Mean streamline patterns around the fence design studied by Huang et al (2012), where H is the total height of the fence; i) sketch of fence design indicating the mean porosity value within the lower half of the fence (ƐL) and the mean porosity value within the upper half of the fence (ƐU) of the fence; ii) 2D mean streamline patterns for the five designs tested. .…”

“…Experimental investigations conducted with a rough bed are very limited despite the fact that in most practical applications the incoming flow develops over a rough bottom boundary (e.g., due to vegetation). Huang et al (2012) performed a wind tunnel experiment to obtain validation data for a numerical study of flow behind porous fences with non-uniform porosity. In their experiments, arrays of identical 2D ribs (roughness elements) were installed at the channel bed in between the inlet of the wind tunnel and the fence, as shown in Figure 2.11.…”

“…So, it is not clear how accurate the statistics calculated from their LES are. Huang et al (2012) performed 2D LES with a dynamic subgrid-scale model to study the flow past a porous wind fence. A finite volume scheme was used to discretize the governing equations for a weakly compressible-flow.…”