Effects of geometrical parameters on the aerodynamic characteristics of a streamlined flat box girder

The effects of aspect ratio (B/D, width to height ratio), wind fairing angle (θ) and relative height of wind nose (H/h, h and H are the distances from the wind nose to the upper and lower surfaces of the girder, respectively) on the aerodynamic characteristics of a streamlined flat box girder were systematically investigated through wind tunnel experiments. A total of 21 cases were tested with B/D = 6, 9 and 12, θ = 45°, 55°, 65° and 75°, and H/h = 1, 2, 3 and 4, which covered most of the typical large span bridges in use. The Reynolds number based on the freestream oncoming velocity U∞ and model height D was 3.3 × 104. The experimental results show that the effects of B/D, θ and H/h are negligible at small wind attack angle (α) with |α| < 4°. The aerodynamic performance of the girder is very sensitive to these geometric parameters at |α| > 4°, which is associated with the states of the flow around the girder. With the increases of |α|, the flow around the girder may transfer from trailing edge vortex shedding (TEVS) to impinging leading edge vortex (ILEV) and leading edge vortex shedding (LEVS). Generally, the girder with H/h = 2-3 and larger B/D and θ corresponds to larger range of α with TEVS, which is favorable to the wind resistance stabilization of the girder.