Analysis of the effect of varying port spacing on initial dilution for a multiport outfall diffuser

Mathematical Models were developed to investigate the effect of changing port spacings on the initial dilution for buoyant jets discharged from multiport outfall diffuser into stagnant, uniform or stratified receiving water.; Two mathematical modeling approaches were used in this research: Asymptotic Solution and Integral Method. Dimensional analysis and characteristic scale arguments provide the essence of the Asymptotic Solution. This has been of particular value in obtaining rough checks on the predictions of mathematical models. Numerical analysis by the traditional Integral Method, which considers the interaction and merging of individual port discharges, has also been performed.; The flow field consists of two zones. Near the source, the individual round jets behave like single jets. At a certain distance away from the discharge point, they merge together and resemble a two-dimensional slot jet. The transition from one zone to the other is taken to be either (1) when the round jet width is equal to the jet spacing, or (2) when the entrainment based on round jet analysis and slot jet analysis are equal. The results for each of these approaches are found to be virtually identical.; The numerical calculations were presented graphically and some interesting physical phenomena were observed. For a typical outfall application discharging into either uniform or stratified ambient fluids, the optimal port spacing to produce maximum initial dilution is 5 ± 1m. The effect of varying the port spacing was predicted quite well by the current models.; To determine the reliability of application of the models, the results from four previous laboratory studies were compared to dilutions calculated from the present model. The model predictions were also compared to previous numerical model studies. These comparisons demonstrate quite convincingly that the results from the current model are much closer than previous calculations to the experimental values, with regard to initial dilutions for ocean sewage outfall diffuser discharging into stagnant water with or without density stratification.