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 (theta) 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, theta = 45 degrees, 55 degrees, 65 degrees and 75 degrees, 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-infinity and model height D was 3.3 x 10(4). The experimental results show that the effects of B/D, theta and H/h are negligible at small wind attack angle |alpha| with |alpha| < 4 degrees. The aerodynamic performance of the girder is very sensitive to these geometric parameters at |alpha| < 4 degrees, which is associated with the states of the flow around the girder. With the increases of |alpha| 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 theta corresponds to larger range of alpha with TEVS, which is favorable to the wind resistance stabilization of the girder.