Optimizing height and porosity of roadway wind barriers for viaducts and bridges

Vehicles and trains are particularly sensitive to wind effects when passing on bridges and viaducts. As a possible countermeasure, wind barriers are considered to be a valuable engineering feature in alleviating an undesirable wind-induced instability of those vehicles. Hence, wind-tunnel experiments are carried out to determine an optimal aerodynamic design of wind barriers for viaducts and bridges. In this study, effects of porosity and height of the wind barrier, as well as orientation of barrier elements on flow and turbulence are studied. Mean velocity fields and vorticity fields are determined using the Particle Image Velocimetry (PIV) technique, while freestream velocities are measured using hot-wires and Pitot tubes. In general, physical phenomena which have been observed as influencing wind conditions behind the wind barrier are freestream wind buffeting, flow separation from a bridge leading edge and wind barrier top, flow bleeding through the barrier. With increasing the barrier porosity, wind velocities behind the barrier increase, particularly in the area immediately downstream from the barrier, while simultaneously there is a decrease in vorticity. Large freestream velocity, as well as vorticity due to flow separation from the wind barrier top, approaches the road surface close to the bridge trailing edge. Increasing the barrier height vertically moves a strong velocity and vorticity away from the road surface. In the paper, two different wind barrier configurations have been tested and analyzed; both orientations of tested wind barrier elements create similar flow field conditions behind the barrier for the same freestream flow and turbulence characteristics. In general, in order to achieve optimal wind conditions for vehicles behind wind barriers on bridges it is necessary to search for a compromise between barrier porosity and height, as these two parameters proved to be the key factors in creating safe transportation environment. In this study, an optimal wind barrier design is considered to be the one with 30% porosity and 5. m high barrier.