Control of flow araund a cylinder by thin shell at a low Reynolds number

In the present work, numerical simulations of the flow around a cylinder with a thin shell are conducted. The Reynolds number studied, which are based on the cylinder diameter (D), was Re=75. The cylinder is covered with a thin shell. The thin shell has three openings on it and has a thickness of 0.005D. The angle between openings is equal. The influence of the following geometric characteristics was investigated: the width of three equal openings on the thin shell, the angle of attack, and the ratio of the outer diameter of the shell to cylinder diameter. The commercial computational fluid dynamics (CFD) package, Fluent® (Ansys®Academic Research CFD, Release 19.1), is employed for all numerical predictions. Plots of force coefficients showed that thin shell is not found to be effective in drag reduction. There is a slight reduction in time-averaged drag (%4.5), but it is not significant. The thin shell is very beneficial to the reduction in RMS lift coefficients. Case M03-11-21 shows the best performance in terms of fluctuating lift force reduction. It is reduced by 41.5% compared to the single cylinder case. However, thin shell is found to be very effective in exciting fluctuating drag and lift forces simultaneously. RMS drag and RMS lift coefficients of the M05-11-20 are 16.3 and 2.24 times larger than those of the single cylinder, respectively. It must be noted that clearance between shell and cylinder, the width of the openings and angle of attack are very important in terms of wake modification.