Abstract
The paper presents Large Eddy Simulation (LES) of flow around two circular cylinders in tandem placed in an open channel. This and the closely related situation of tandem cylinders in a passage are rich of complex flow phenomena and of considerable practical and fundamental interest. The configuration was set up to correspond closely to an experiment (Ataie-Ashtiani and Aslani-Kordkandi Flow Turbul. Combust. 90(3), 471-490 (2013)) with detailed velocity measurements. The ratio of the distance between the cylinders, L, and the cylinder diameter, D, and the ratio of water depth h to D, are L/D=3 and h/D=3.1, respectively, as in the experiment. However, a lower Reynolds number had to be used and a smooth channel wall instead of a somewhat rough wall in the experiments. The Reynolds numbers based on channel height and cylinder diameter are 22,600 and 7,300 respectively. A fine grid was employed so that the LES is well resolved and the results are little affected by the subgrid-scale model (dynamic Smagorinsky) and represent well the actual physical processes of the situation studied. A comparison with experimental results of mean flow, turbulence quantities and shedding frequency shows that there is good agreement about all the main features, but there are some quantitative differences as the flow situations differed in some respects. The complex 3D flow behaviour is analyzed and described with the aid of the LES results, and these also provide benchmark data for testing other, less costly calculation methods which are preferred in practice.