Investigation Of Force Analysis And Turbulent Characteristics In The Flow Past Two Side-by-side Circular Cylinders With Different Diameters

Multiple-pipelines of different diameters in pipe pave have been widely applied on the deep ocean development. At present, study in flow behaviors and vortex-induced-vibration (VIV) of multiple-pipelines with different diameters is not much. Therefore, flow around multiple-pipelines with different diameters has been one of the significant problems in fundamental research and engineering field.The 3-D turbulent flow around two side-by-side circular cylinders with different diameters, at sub-critical Reynolds number (Re=3900), is numerically studied by large eddy simulation (LES) and the results are analyzed by empirical mode decomposition (EMD) method. The analysis on application example of flow control apparatus is also carried out. Main results are focused on vortex frequency, drag and lift coefficients, coherent structure and scale properties. The main results are given as follows:First, spacing ratios have effect on drag and lift coefficients of two cylinders. When T/D equals to 1.2, the vortex shedding of main cylinder is strongly suppressed by the small cylinder and endure the minimum force. When T/D equals to k5, the vortex shedding of the main cylinder can be improved and the main cylinder can endure the maximum force. At large T/D, the force characteristics tend towards stability. Spacing ratios also have effect on the wake characteristics of two cylinders. Biased flow exists when T/D=1.2 and disappear when T/D=1.5.At large T/D, the vortex shedding frequency of two cylinders decreases first and then increases and tends towards stability at last.Second, coherent structures play a principal role in the process of vortex shedding. There is a linear relationship between the mean frequency of each mode and the modes order on semi-log coordinate. The mean vortex shedding period and mean energy of single circular cylinder are analyzed well by EMD method. The vortex shedding period of a cylinder is consistent with the period of the restructured coherent structures quantitatively.Finally, the vortex shedding of a cylinder is strongly suppressed by fairing. The drag and lift coefficients of a cylinder with fairing can be greatly improved. And the drag and lift coefficients of two side-by-side cylinders with fairings reduce evidently.