Avaliação do desempenho de redes de drenagem urbana em condições de escoamento transiente

Abstract

The pipes of urban drainage networks are designed to carry rainwater in free flow, but, during extreme events, they can fill quickly, exceeding the capacity of the pipes and triggering the occurrence of transient phenomena. Air trapping and the formation of geysers represents one of the most extreme conditions in the flow of drainage networks, however, understanding about the formation of these air and water interaction phenomena is still scarce. Although experimental and numerical studies provide important information, the limited availability of suitable tools for designers questions the effectiveness of widely used models, such as the Storm Water Management Model (SWMM), to represent or at least identify the occurrence of transient conditions that indicate the need for more in-depth studies on drainage systems. Therefore, this study seeks to develop strategies and methodologies to experimentally and mathematically evaluate the performance of transient flow conditions in urban drainage networks, using two experimental geometries. The first aims to evaluate the formation of geysers in a drainage network with a ventilation tower upstream, not yet evaluated in previous studies, and considering different combinations of air volume, water level in the tower, opening of the guillotine valve and diameter of the tower. The second considers a horizontal network with a T-junction at 90° and transient flow presented by Pinto et al. (2021), considering different flows and slopes. From the experimental data, a preliminary analysis of the localized pressure loss coefficient (K) for the T-junction was carried out with a view to calibrating the model developed in SWMM, in order to obtain a model that is capable of simulating specific flow conditions. transient. The results indicated that the smaller diameter of the ventilation tower and its upstream allocation generates geysers of greater magnitude, and are also strongly affected when the air release into the network is rapid. When investigating pressure loss in T-junctions, SWMM showed promise in terms of its ability to simulate two-phase flow, making it possible to calibrate the model regarding the parameter K at the junction. It was found that K is dependent on the flow rates in each section, with less influence from the slope. High values are verified for scenarios in which there is flow coming from the two sections upstream of the junction, differing from studies found in the literature. Furthermore, the research provided a deeper understanding of the behavior of water and air in drainage systems and the formation of geysers, in addition to generating a base of information on the pressure loss coefficient parameter in T-junctions, making it possible to investigate in studies future use of SWMM as a tool for complex hydraulic simulations, promoting advances in modeling networks with transient flow.