The effects of turbulence on the aerodynamics of long-span bridges

Atmospheric flows are turbulent. Experimental analysis of wind-induced vibration problems must. address this issue by either matching turbulence characteristics completely or by acknowledging uncertainty in conclusions as a result of imperfect simulations. Because the former is for all practical purposes currently impossible, the latter must be understood as fully as possible.; This experimental study of the effects of turbulence on long-span bridge aerodynamics examined the anatomy of turbulence effects on the self-excited forces responsible for flutter and investigated the spanwise correlation of the overall aerodynamic lift and moment. A forced-vibration technique was used with a model of rectangular cross section instrumented with 64 pressure transducers. Spanwise coherence measurements were made on both stationary and oscillating models in a series of smooth and turbulent flows.; Unsteady pressure distributions were examined to observe turbulence-induced changes in the self-excited forces. This allowed a clearer understanding of turbulence effects than was possible by observing only integrated quantities such as flutter derivatives. For the cross section studied, turbulence stabilized the self-excited forces. Regions of maximum pressure amplitudes were observed to shift toward the leading edge with increasing turbulence intensity—similar to the behavior observed in pressure distributions on stationary bodies. This upstream shifting was responsible for the bulk of the changes in the overall stability characteristics.; Spanwise correlation was quantified for both total aerodynamic forces and for self-excited and buffeting components separately. Self-excited forces showed essentially unity coherence for the entire spanwise separation range studied (2.4B). This supports the assumption common in analytical estimates of fully correlated self-excited forces. It does not, however, support the hypothesis that the stabilizing effect of turbulence observed in full aeroelastic tests is due to a turbulence-induced decrease in the spanwise coherence of the self-excited forces. In the future, greater spanwise separations need to be tested for full understanding of this behavior. Spanwise correlation of the buffeting force components showed exceptional similarity between stationary and oscillating model tests.