NUMERICAL MODELLING OF AIR-WATER FLOW IN A VERTICAL DROP MANHOLE

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NUMERICAL MODELLING OF AIR-WATER FLOW IN A VERTICAL DROP MANHOLE. Vitor Sousa IST, UTL Inês Meireles UA Jorge Matos IST, UTL Maria do Céu Almeida LNEC. OUTLINE. Introduction Experimental study Numerical code Numerical model implementation Conclusions. 1. INTRODUCTION.

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### NUMERICAL MODELLING OF AIR-WATER FLOW IN A VERTICAL DROP MANHOLE

Vitor Sousa

IST, UTL

Inês Meireles

UA

Jorge Matos

IST, UTL

Maria do Céu Almeida

LNEC

OUTLINE

Introduction

Experimental study

Numerical code

Numerical model implementation

Conclusions

1. INTRODUCTION
• Dissolved oxygen concentration is one of the most relevant parameters used in water quality assessments, both in natural and artificial streams.
• In sewer drops, the presence, or absence, of dissolved oxygen is of significance in relation to the build-up or persistence of sulphides.
• Only a limited number of prototype or model studies involved the use of vertical drops in circular channels, conveying either clean water, polluted river water or wastewater.
• Up to date, numerical modelling of turbulence and air entrained generated aeration has been mainly focused on artificial aerators, such as bubble plums.
• CFD – Computer Fluid Mechanics has emerged as na alternative research tool in several fields:
• increasingly complete models and more efficient models
• increase of the computational capability of personal computers
3. NUMERICAL CODE

The commercial code FLOW-3D®, developed by Flow-Science, Inc, was selected for this research due to its particularly efficient, robust and accurate method to simulate free-surface flows.

The Reynolds-Averaged Navier-Stokes (RANS) mixture equations are used in the theoretical model:

3. NUMERICAL CODE
• The code allows for independent mesh and geometry definition due to the FAVOR method. Single- or multi-block grids can be used to define the domain in FLOW-3D, where the geometry can be incorporated through:
• a “solid modeler,” which allows for the use of general quadratic functions
• topographic data
• Unlike other codes, the FLOW-3D does not need to simulate the air flow over the free surface due to the TruVOF method. The TruVOF requires three key elements to be implemented, centred in the resolution of the function of the fraction of fluid through:
9. CONCLUSIONS

The simulations performed in this study show that the use of a RNG model combined with the TruVOF method allows for an adequate overall representation of the flow features in terms of water depth and pressure head

The activation of the model of air-entrainment was found crucial for the accuracy of the simulation of the pressure head of the air-water flow along the invert of the outlet channel.

The model chosen for this stage of the research is a simplified representation of many drainage systems where free drops exist at the manholes, particularly in older systems.

The results show that the code seems to simulate air-water flows down vertical drops correctly, particularly its effect in terms of pressure head.

### RISK ASSESSMENT OF SEWER CONDITION USING ARTIFICIAL INTELLIGENCE TOOLS Application to the SANEST sewer system

Vitor Sousa

IST, UTL

José Pedro Matos

IST, UTL

Nuno Marques Almeida

IST, UTL

José Saldanha Matos

IST, UTL