Nicolle, A.; (2009) Flow through and around groups of bodies. Doctoral thesis , UCL (University College London).

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Abstract

Fluid flows often consist of multiple bodies either filling most of the flow domain (for instance, porous media) or grouped in localized regions. Flow through localized groups containing many bodies has, hitherto, had little detailed study. The primary objective was to develop and trial new numerical and experimental procedures that make possible detail studies of complex multibody flows. The research investigates flow through a circular array of fixed size and populated by different numbers of equally spaced cylinders, allowing the void fraction (φ) to be varied. The main contribution is a detailed fully-resolved two-dimensional numerical calculation of flow past arrays containing from 1 to 133 cylinders, where the array Reynolds number is 2100. To produce this, a parallel computational code has been written, specifically for a supercomputer, in general object-orientated language using late binding and high performance numerical libraries (PETSc, MKL and ParaMETIS). New diagnostics were applied to understand the array’s influence on the flow through and around the array. A linear model was used to interpret the results. An experimental apparatus was designed to measure and vizualize the flow field and force contributions from an array fixed in a uniform flow. The design concept (including the flume, instrument array and electronics) was tested and optimized using CFD and FEA. The experimental results provide insight into the difference between two- and three-dimensional flow patterns. Case studies and experiments have generated data and graphical images at a level of resolution not previously possible. Three distinct regimes have been identified. For low φ, the interaction between the individual cylinders is weak. For intermediate φ, a shear layer is created and stabilized by the bleed flow through the group, resulting in steady forces on the group. For high φ, strong blocking occurs and the array acts like a solid cylinder.

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