Developments in mathematical simulation of fluid flow in building drainage systems

Abstract

A mathematical model utilising the Method of Characteristics to solve the equations of continuity and momentum in a finite difference scheme forms a computer based simulation package - AIRNET. It can simulate conditions in building drainage, waste and vent systems. Recent work extended AIRNET by including the effects of detergents and temperature. Other work examined the motive force of the water, extending it to include a proportion of the discharge appearing as droplets falling in the central air core as opposed to assuming it was due entirely to an annular film. This article includes these additions and links to previous work on non-dimensional analysis, to yield a more refined AIRNET model which includes the effects of detergents, temperature and droplet fraction. Significant refinement of the AIRNET model is described in this article. Practical Applications: Accurate simulation of detergent dosed waste as described here extends the scope over which accurate simulations and code guideline comparisons can be made, to include ‘live’ domestic and industrial media from modern appliances and practices. This will have a significant impact on code generation and drainage system design practices, allowing optimisation for reliability, effectiveness and cost. This article improves the current level of understanding of the hydraulic basis for the design requirements imposed on sanitation engineers and code bodies, and improved an existing computer simulation model in its capacity as a design tool.