LARGE EDDY SIMULATION OF FLOW PAST TWO CONICAL CYLINDERS IN TANDEM ARRANGEMENT

In order to explore the time-averaged drag coefficient, fluctuating lift coefficient characteristics and flow field mechanism of two conical cylinders in tandem arrangement, large eddy simulation is used to simulate two conical cylinders in tandem arrangement with a spacing ratio of 2−10 at Re = 3900. The two spanwise asymmetric reflux zones formed behind the upstream conical cylinder make the en dash pressure distribution behind it asymmetric. The upwash, downwash and side shear layers developed by the upstream conical cylinder are the main reasons for the variation of the time-averaged drag coefficient and the fluctuating lift coefficient of the upstream and downstream conical cylinders. The flow structure between tandem two conical cylinders can be divided into three states with the change of spacing ratio: in the shear layer wrapping state, transition state and wake impact state. Shear layer wrapping state, the dominant incoming flow at the free ends of the upstream conical cylinder has a wide range of influence on the windward side of the downstream conical cylinder. The shear layer of the upstream conical cylinder completely wraps the downstream conical cylinder, inhibiting the formation of the backflow zone behind the downstream conical cylinder, causing a decrease in the time-averaged drag coefficient of the downstream conical cylinder. In the wake impact state, the wake of the upstream conical cylinder is fully developed, and the size of the recirculation zone does not change with the spacing ratio. The wake of the upstream conical cylinder periodically falls off and hits the surface of the downstream conical cylinder, which greatly increases the pulsating lift coefficient. The maximum fluctuating lift coefficient is about 20.7 times higher than that of a single straight cylinder. In the transition state, the time-averaged drag coefficient and the fluctuating lift coefficient will both increase compared with the shear layer wrapped state. This research can provide theoretical support for the layout of wind energy harvesting structures.