Reservoir CFD modelling - what are the benefits of using a 3D model?

Water utilities own and operate a number of potable water reservoirs throughout their water supply network. The behaviour of water in reservoirs can impact on water quality. It is interesting to understand the movement of water within water tanks in order to ensure that potable water is not held up in “dead zones” as increased residence time results in residual chlorine decay that augments the risk of recontamination in the network.

Reservoir models can assist in finding efficient and cost effective solutions to ensure satisfactory flow path within reservoirs by assessing the impact of baffle curtains and/or comparing different layout options. In general 3D Computational Fluid Dynamics modelling is recommended to provide detailed solutions that involved fluid flows. However 3D models are often complex to build and have long runtimes which can make them prohibitive costs.

The main objective of the work described in this paper was to investigate the possibility of using simpler 2D open-channel software for modelling flows in water tanks where the reservoir layout does not significantly differ in depth. A case study was used to compare the simulation results from a 3D CFD model to those from 2D computations. Comments are made regarding the limitations of 2D modelling and the extent in which 2D models can be used to estimate the movement of the water in reservoirs.