Numerical simulation and assessment of the effects of operation and baffling on a potable water service reservoir

Abstract

A major water-quality concern in a potable water service reservoir is the potential loss of chlorine residual, which is closely related to the flow pattern. In this article, the effects of operation and baffling on the flow pattern and chlorine-concentration distribution in a potable water service reservoir are reported. Using a computational fluid dynamics (CFD) method coupled with dynamic meshes, actual service conditions are mimicked, which have seldom been reported in the literature. First, this article provides an insight into why manipulating the valve located at the inlet can be beneficial in enhancing water quality in the long run. An explanation based on the simulation results suggests that manipulating the valve located at the inlet can lead to the evolution and migration of the vortices in the service reservoir, which would then allow water with prolonged age to flow out of the reservoir. This is significant for the operation of service reservoirs. Second, it explores the possibility of retrofitting a service reservoir with baffle walls to minimize the probability of seriously diminished water quality resulting from poor mixing and excessive aging. Although adding baffle walls in the flow-recirculation regions is found to break up the vortices and thus shorten the flow path, the fluid-velocity magnitude is reduced after flowing past the baffle walls. The outcome of these conflicting effects may eventually lead to a diminished effluent chlorine concentration after adding the baffle walls. © 2013 American Society of Civil Engineers.