STREAMING-FLOW INDUCED BY AN OSCILLATING CASCADE OF CIRCULAR-CYLINDERS

The fluid flow induced by a cascade of circular cylinders which oscillates harmonically in an unbounded, incompressible, viscous fluid which is otherwise at rest is investigated both numerically and experimentally. Attention in this paper is mainly concentrated on the induced steady streaming flow which occurs when the ratio of the amplitude of the oscillation of the cascade to the size of the cylinder, epsilon is very small. The leading-order flow is then governed by the steady Navier-Stokes equations. In order to solve these equations numerically we first generate numerically a grid system using the boundary element method and then use a finite-difference scheme on the newly generated rectangular grid system. Numerical results show that for small values of the streaming Reynolds number R. there are four recirculating flows of equal strength around each circular cylinder of the cascade. At large values of R. symmetry breaks down and numerical solutions are found for asymmetrical flows. Numerically, a critical value of R(s), R(s0) say, is identified such that the flow is symmetrical when R(s) < R(s0) and asymmetrical when R(s) > R(s0) and these results are in reasonable agreement with experimental results, which are also presented in this paper.