College of Harbour, Coastal and Offshore Engineering, Hohai University
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 = 100. 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 2S and a combination of 2S* and 2S. 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 2S, P+S and 2S* 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.