Flow through a very porous obstacle in a shallow channel

Alistair Borthwick, Maggie Creed, Scott Draper, Taka Nishino

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

A theoretical model, informed by numerical simulations based on the shallow water equations, is developed to predict the flow passing through and around a uniform porous obstacle in a shallow channel, where background friction is important. This problem is relevant to a number of practical situations, including flow through aquatic vegetation, the performance of arrays of turbines in tidal channels, and the hydrodynamic forces on offshore structures. To demonstrate this relevance, the theoretical model is used to (i) reinterpret the core flow velocities in existing laboratory-based data for an array of emergent cylinders in shallow water, and (ii) reassess the optimum arrangement of tidal turbines to generate power in a tidal channel. Comparison with experimental data indicates a maximum obstacle resistance (or minimum porosity) for which the present theoretical model is valid. When the obstacle resistance is above this threshold the shallow water equations do not provide an adequate representation of the flow, and the theoretical model over-predicts the core flow passing through the obstacle. The second application of the model confirms that natural bed resistance increases the power extraction potential for a partial tidal fence in a shallow channel and alters the optimum arrangement of turbines within the fence.
Original languageEnglish
JournalProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Early online date26 Apr 2017
DOIs
Publication statusPublished - Apr 2017

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