SMaRT-OnlineWDN D4.2 : Investigation sur les mécanismes des phénomènes spécifiés

Abstract

The main objective of the SMaRT-OnlineWDN project is the development of an online security management toolkit for water distribution networks that is based on sensor measurements of water quality as well as water quantity. Pseudo-real time modelling of water quantity and water quality variables is the cornerstone of the project. Existing transport model tools are not adapted for online modelling and ignore some important phenomena that may be dominant when looking at the network in greater detail with an observation time of several minutes. The aim of this deliverable is to report investigations by the SMaRT-OnlineWDN partners regarding processes of contaminant mixing at junctions and transport in pipes. Firstly, investigations at the Berliner Wasserbetriebe (BWB) are presented (section 1). The test field is a simple loop with old cast iron pipes representative of old pipes in the BWB network. Chemicals can be injected into the pipe by a pump and three multi-parameter sensors, located at different distances, measure hydraulic and quality parameters (flow, pressure, conductivity pH-value, oxygen,…) during the flow. This network was calibrated for the roughness and the effective diameter of pipes which is reported here. Experiments with salt and its transport under different regimes was also studied. So the transport phenomena like advection, dispersion and absorption can be studied. Next, a statistic and hydraulic analysis of the Tee and cross-junctions is achieved on the two networks in France (Strasbourg CUS) and Vedif network (demand area of Villejuif) ) (section 2). It was found that there are a lot of cases where double tee-junctions are present with a distance inter-tee inferior to 10 diameters which may favour imperfect mixing. A hydraulic analysis was also performed which ensures that every hydraulic regime is well represented. For example, for a double-tee junction with equal 100mm diameter 40% of the Reynolds cases are for laminar flow and 80% are under 10,000. For higher diameters the statistics fall to 20% for laminar flow and 60% under 10,000. The results of this analysis serve to design the new test rig built in Dresden by TZW and supply CFD cases for the numerical simulation. Finally, in section 3, the new test rig at TZW (Dresden) and all the investigations that were necessary to know which product to inject, the injection system and the experimental setup are presented. First investigations at TZW have been performed applying several colour tracers with different densities under laminar and turbulent flow conditions The experiments were conducted in a straight pipe with velocities in a range of 0.004m/s to 0.5 m/s. The main results under laminar flow conditions are: 1) Dispersion is the main process for spreading and mixing, 2) The behaviour (moving up or down) of the tracer depends particularly on the density of the injected liquid, 3) An injected liquid with a higher or lower density than the water moves at the pipe wall with a lower velocity than the water body