A study of unsteady flow wave attenuation in partially filled pipe networks

Abstract

The attenuation of unsteady flow in building drainage systems must be fully considered if water conservation proposals involving changes in flush volume or pipe diameter are not to lead to solid deposition and subsequent blockage of the drainage system. Empirical methods of studying attenuation are limited in their application and there is a need for a time-dependent numerical model to simulate flow in the building drainage system. A number of numerical solutions to the time-dependent unsteady flow equations were considered and the method of characteristics was chosen for its suitability and proven usefulness. Full-scale flow tests were undertaken in the laboratory to validate the use of the method of characteristics and the results justified the development of a network model incorporating subsections to simulate end boundaries, junctions and multiple inflows. The final computer model of the building drainage system was completed using a representation of flow in a vertical stack based on work published elsewhere. The program is capable of simulating multi-storey drainage systems with multiple flow inputs and variable boundary and junction types. It is restricted to level invert junctions and requires the steady-flow depth characteristics of each type of junction within the program. The program can be used to output depth or flow rate through time at any point in the system and could therefore be used by a designer to evaluate the performance of new systems. The program could also be used to determine the effects of water conservation legislation on system design.