Papers by Author: Fu You Xu

Abstract: The results of unsteady Reynolds averaged Navier-Stokes (URANS) simulations of flow around a square cylinder using two-dimensional hybrid meshes were presented in this paper. The first part examined the accuracy of various RANS turbulence models, i.e. the standard model, RNG model, realizable model, standard model, SST model, and RSM, by comparing their results with available experimental data. Despite the limits imposed by the RANS approach and the relatively inexpensive two-dimensional computations, the main features of this complex flow can be predicted reasonably well. Among the computations using various RANS models compared here, the SST model shows the best agreement with the experiment. The second part investigated the effects of corner cutoffs on unsteady flow characteristics around a square cylinder by using the SST model. Especially the detailed near-surface flow structure around the cylinder was focused on, aiming at giving an explanation for the drastic modification of the aerodynamic characteristics as the corner shape is slightly changed.

Abstract: The vortex resonance characteristics of one typical streamlined bridge girder are studied using surface pressure measuring technique. Based on the testing results in smooth and turbulent flows with different attack angles, the means, standard deviations, power spectra of fluctuated pressures, as well as the correlations between local and total aerodynamic forces are comprehensively analyzed, and the torsional vortex vibration mechanism is disclosed. The research results indicate that, for the vortex resonance case, the flow separation at upper and lower surfaces is more severe than that of non-vortex case. The upper surface pressure fluctuation at the middle and downstream region is most obvious, which is incurred by the flow separation at the upper surface upstream tip. At the middle and downstream region, the aerodynamic forces keep good correlations with the total forces, and they provide the major torsional moment for vortex resonance. Vortex vibration depends on both fluctuation intensity and peak location. For the vortex resonance case, the surface fluctuated pressures are locked in the same frequencies.

Abstract: Long-span flexible bridges are always challenged by fierce wind load, and the wind with extreme-attack-angle may be a potential danger to threaten the bridge security. The three-component coefficients at extreme attack angles of the section model of one flat streamlined box-girder and central slotted box-girder are investigated through the wind tunnel test, and the detailed explanation are made. The results show that lift and pitch coefficients change approximately linearly between stall angles, and the coefficients display significant nonlinearity and a certain pulsation phenomenon when the attack angle exceeds stall angles, and the stall angles should not be less than ±10° for the sake of the safety of bridges.