Arrangement Effects on Flow Through an Array of Cylinders

Although elements in natural and engineered systems, such as patches of aquatic vegetation, groups of pile foundations, and arrays of tidal stream turbines, are arranged in uniform or random configurations, there is a lack of understanding of hydrodynamic differences between these two arrangements. This paper presents results from two-dimensional direct numerical simulations of flow through a circular array of cylinders that have been undertaken to examine the hydrodynamic differences. It is shown that a random array has higher average drag coefficient and lower spatially averaged velocity within the array than these of a uniform array with the same diameter ratio. The lower drag coefficient for the uniform array is associated with the formation of characteristic flow structures, including two-row structure and shear layer reattachment and channelized flow in between adjacent lines of cylinders. As increasing perturbation of the array, these characteristic flow structures and the channelized flow progressively break down and hence the average drag coefficient increases and the spatially averaged velocity decreases. This paper provides guidelines for optimizing hydrodynamics of obstacle arrays through altering arrangement in real systems.