CFD Analysis on Current Flow Past Two Large Rectangular Cylinders in Tandem

Abstract

The motivation of this work came from the design and construction of a new suspension bridge in the Tacoma Narrows next to an existing bridge. The new bridge like the old one was designed to be supported on two large concrete piers at its two ends. The new caissons were in close proximity to the piers of the existing bridge. The two caissons were built floating in place so that the draft of the caissons continually increased as the construction progressed. In order to determine the forces due to the current flow around the piers CFD analysis was made for a large number of cases. The Reynolds number of the flow around the piers was on the order of 108 (100 million). The commercial software AcuSolve was employed to solve for the flow field around the pier/caisson assembly and the current forces were derived numerically. Most of the CFD runs were made in full scale. However, a few runs were also made in a model scale. This allowed a comparison of the results between the full and model scale so that any scale effect could be studied. This paper makes detailed analysis of the fluid flow past the piers, their interaction and shadowing effects. The effect of the variation in the current flow direction is also investigated. Critical analysis of the variation of the drag and lift coefficients with Reynolds number, spacing parameters, and Strouhal number are made in this paper. The time varying inline, transverse lift and vertical forces are also studied. In view of the analysis results the feasibility and accuracy of the CFD results for such high Reynolds number are examined. The results herein have obvious applications not only in coastal engineering problems, but in several offshore applications as well.