Flow Field Mechanism of Wake Interference Effects on Aerodynamic Characteristics of a Downstream Circular Cylinder

Abstract

To clarify the mechanism of wake interference effect on the downstream cylinder, large eddy simulation（LES） method was adopted. The flow around two static staggered circular cylinders was studied at a high Reynolds number of Re=1.4×105, and the ratio of center-to-center pitch （P） to the diameter of the cylinder（D） ranges from P/D=1.5~4. The aerodynamic coefficients, mean pressure distributions, and flow field of the downstream cylinder were discussed along with the changing of incidence angle. The relationship between aerodynamic forces and flow characteristics was analyzed based on the time-averaged wall shear stress and flow structures. The results show that the reasons for the negative drag force of the downstream cylinder at small pitch ratio（P/D<3） lie in two factors, i.e., a pair of recirculation zone with opposite direction for the tandem configuration and the high-speed gap flow for the staggered arrangement with small incidence angles. At small pitch ratios（P/D=1.5~3），the downstream cylinder is subjected to remarkable mean lift coefficient（inner lift），which is caused by the shift of the stagnation point, high-speed gap flow, and separation bubble. At the moderate pitch ratios（P/D=3~4），the mean lift（outer lift） of the downstream cylinder is affected by the shift of the stagnation point and separation point in the gap side.

Keywords: two circular cylinders,  large eddy simulation,  high Reynolds number,  lift mechanism,  negative drag mechanism