Estimation of Unsteady Pressure Distribution on Bluff Bodies Based on Vortex Shedding Panel Method : Case of Oscillating Rectangular Cylinders in Uniform Flow

Abstract

One of the most important things for designing a structure of bluff shape in unsteady current, is to predict in advance the unsteady forces due both to the unsteady flow and to its oscillating motions. But, it seems that there has been no practically reliable methods of predicting the flow and forces around such an oscillating bluff body even in 2-dimensional case. On this point of view, the authors have recently developed a new Vortex-Shedding Panel Method suitable for both lifting and non-lifting problem for an arbitrary 2-dimensional section in steady flow. The un-knowns are source and vortex densities distributed on the body surface, in which the surface boundary conditions are specified both outside and inside the surface. This leads to a well-posed problem in mathematical sense, forming a Fredholm type integral equation of the 2nd kind, and ensures steady convergence in numerical computation, differing from usual discretization methods. In this paper, a general unsteady problem for oscilating bluff section under unsteady incoming flow is studied and numerical examples are also shown for the case of oscillating rectangular cylinders in uniform flow. The results of it show quite good agreements with experimental data in aspects of the hydrodynamic oscillating forces and the pressure distribution on the body surface.