Q. Zhai - College of Harbour, Coastal and Offshore Engineering, Hohai University
H. K. Wang - College of Harbour, Coastal and Offshore Engineering, Hohai University
G. L. Yu - School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University

Flow past two tandem triangular cylinders forced to oscillate transversely in a uniform flow, is numerically investigated at a Reynolds number Re = ۱۰۰. The incompressible Navier-Stokes equations in Arbitrary-Lagrangian-Eulerian formulation are solved by four-step fractional finite element method. The two cylinders are oscillated in phase and their motions are limited to low amplitudes with a wide frequency range. This study focuses on two typical spacings between the two cylinders, corresponding to vortex suppression (VS) regime and vortex formation (VF) regime respectively for flow past two stationary cylinders. Numerical results show that the response characteristics of two cylinders are significantly affected by the spacing, oscillation amplitude and frequency. For the VS spacing, both cylinders have a wider lock-on region, especially at relatively larger amplitude and higher frequency; the downstream wake patterns are mainly ۲S and a combination of ۲S* and ۲S. However, for the VF spacing, the lock-on frequency range of the cylinders is even slightly narrower than that of a single oscillating cylinder; the wake field is more complex since it may comprises ۲S, P+S and ۲S* structures at some higher frequencies. Additionally, the hydrodynamic forces are also discussed in terms of mean and root mean square quantities, and reveal large differences between oscillating and stationary cylinders.

Two triangular cylinders, Forced oscillation, Response characteristics, Wake pattern, Hydrodynamic Force