Research on wind barrier of canyon bridge-tunnel junction based on wind characteristics

Due to the acceleration effect of the wind by the special geographical location of the canyon bridge-tunnel junction, the traffic safety and stability of this section are difficult to be guaranteed, resulting in frequent traffic accidents. In order to ensure the safety and comfort of vehicles driving on this section, the numerical simulation method based on CFD is adopted to establish the numerical model of the canyon bridge-tunnel junction. The acceleration of the incoming wind speed in the bridge-tunnel junction with a guardrail that is 0.8 m high is analyzed from different canyon spacings, wind directions and heights from the bridge deck. Based on the characteristics of wind field above the bridge deck, two kinds of gradient wind barriers—trapezoidal and stepped—are proposed, and their wind reduction effects and turbulence intensity changes are analyzed. Then the aerodynamic performances of running vehicle are compared. The results show that the stepped wind barrier with 50% porosity and rectangular section railings has the best wind reduction effects, and can noticeably improve the comfort of driving. The aerodynamic coefficients of vehicle are lower with stepped wind barrier.

A Wind Tunnel Study of the Seasonal Shelter Efficiency of Deciduous Windbreaks

HighlightsSeasonal leaf shedding is a key factor affecting the airflow field and shelter efficiency of deciduous windbreaks.The wind deceleration region around modeled Elaeagnus angustifolia L. (Russian olive) windbreaks was larger in winter than in summer, but the intensity of the wind speed reduction was relatively low.The shelter efficiency of E. angustifolia windbreaks in winter was not less than 80% of that in summer.Abstract. The shelter efficiency of windbreaks constructed with deciduous plants changes with their phenological stage. We used Elaeagnus angustifolia L. (Russian olive) as an example and investigated the airflow field and shelter efficiency of deciduous windbreaks with summer facies (with leaves) and winter facies (without leaves) by means of scaled wind tunnel simulation experiments. Our study revealed that different canopy seasonal porosities exert different wind speed reductions inside the windbreaks, which also determine the upwind and downwind wind speed variation. The variation in wind speed was greater in summer than in winter. For the windbreak with summer facies, a large wind acceleration region above and before the windbreak and a strong wind deceleration region inside and after the windbreak were observed. The wind deceleration region around the windbreak with winter facies was larger than that in summer, but the intensity of the wind speed reduction was relatively low. The results of our study further show that although E. angustifolia windbreaks are highly porous in winter, the shelter efficiency was not less than 80% of that in summer. Like any wind tunnel study on windbreaks, producing an artificial plant model that is highly similar to the real field plant is difficult. Nevertheless, our results clearly revealed the wind reduction patterns of deciduous windbreaks due to seasonal porosity caused by leaf shedding, which may provide valuable data for assessing the shelter efficiency of deciduous windbreaks. Keywords: Airflow field, Elaeagnus angustifolia, Seasonal porosity, Wind reduction.

Numerical Simulation and Experimental Verification of Butterfly Porous Fences

In this paper, the domestic and foreign research progress of numerical simulation on the porous fence is introduced briefly, and a numerical model is established to simulate the flow characteristics behind the butterfly porous fence through the FLUENT software. The comparison results found good agreement between the numerical model and wind tunnel experimental data with an error of 7.8% in the wind reduction ratio, indicating the present numerical model can be used to undertake study on butterfly and non-planar porous fences. The effect of porosity on the flow characteristics behind the butterfly porous fence have been evaluated using the present model to determine an optimum porosity for sheltering effect of an isolated porous fence. As a result, the butterfly porous fences with a range of porosity from 0.27 to 0.32 seem to have a better shelter effect among the studied porosities, and all the wind reduction ratios approach to 60%.

Effect of a Bottom Gap on the Flow Characteristics behind Non-Planar Porous Fence

The flow field behind non-planar porous fence of geometric porosity ε=0.273 with various bottom gaps (G) has been investigated by hot-wire anemometer velocity field measurement technique in a wind tunnel experiment. Seven gap ratios G/H=0.000, 0.025, 0.075, 0.125, 0.150, 0.175, 0.200 of non-planar porous fence were tested in this study with the free-stream velocity fixed at 10m/s. The experimental data were analyzed and the turbulence intensity and wind reduction ratios for different gaps of the porous fence were calculated to estimate the shelter effect of a non-planar porous fence model. The results show that the gap ratio G/H=0.150 gives the best shelter effect among the seven gaps of the non-planar porous fence tested in this study, having a better mean velocity and turbulence intensity as well as wind reduction ratio in a large area behind the non-planar porous fence.