## Numerical simulation of oscillating-cylinder effects on a downstream cylinder wake using lattice Boltzmann method
## RésuméThis paper proposes to use a newly developed lattice Boltzmann technique to simulate the wake of a streamwise oscillating cylinder in the presence of a downstream stationary cylinder. The oscillating frequency ratio f is the oscillating frequency of the upstream cylinder and _{e}f is the natural vortex shedding frequency of an isolated stationary cylinder, and the oscillating amplitude _{s}A is fixed at 0.5 cylinder diameter, D. Three typical flow structures, depending on f have been identified at the cylinder center-to-center spacing _{e}/f_{s}L/D = 3.5, which are in excellent agreement with experimental data. The flow structure remains unchanged for the same f as _{e}/f_{s}L/D is increased to 6.0, but changes drastically at a low f for _{e}/f_{s}L/D = 2.0. It is proposed that, beyond a critical L/D, vortices are formed between the cylinders and the flow structure is independent of L/D. But, below the critical L/D, the free shear layers separated from the upstream cylinder may reattach on the downstream cylinder, thus leading to a different flow structure from that above the critical L/D despite of the same f and _{e}/f_{s}A/D. The lift and drag coefficients associated with the two cylinders are examined in detail for each flow structure. |

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