Flow Distortion Recorded by Sonic Anemometers on a Long-Span Bridge

Abstract

Eight months of sonic anemometer records, collected above the deck of a long-span suspension bridge in complex terrain, have been used to assess possible distortion effect of the bridge girder on the monitored flow. For the two main wind directions observed on the bridge site, the velocity records from the downwind side of the deck, in particular, the vertical wind component, are systematically affected by the bridge deck. More precisely, the friction velocity and the variance of the vertical wind fluctuating component are underestimated on the downstream side of the deck. For a deck height H, both the anemometers located on the downwind side, on the same hanger, at a height of 3.6H and 2.2H show a substantial level of flow distortion. This indicates that flow distortion issues can be mitigated more efficiently using anemometers on both sides of the bridge instead of mounting them as high as possible above the deck. The influence of terrain-induced flow distortion is also found to be non-negligible, such that turbulence characteristics significantly different than observed in flat and homogeneous terrains are found.