Encyclopaedia Index
Transport and fate of a toxic spill

### TITLE : Transport and fate of a toxic spill

BY : Dr S V Zhubrin, CHAM Ltd

DATE : October 2022

FOR : Demonstration case for PHOENICS 2022 v1.0

### INTRODUCTION

An application of multicomponent chemical reaction system model is presented aimed at the at the simulation of the relevant physicochemical phenomena taking place in a real-life environmental case study.

### PHYSICAL SITUATION

The case deals with the chemicals steadily spilled into a river section of complex topography from a point source located upstream of the island array.

It is supposed that a spill consists of two initially neutral components, A and B, with a fixed mass fractions at the spill site location.

The components react on entry and steady two-step chemical reaction is in progress producing the two highly toxic final, D and E, and one intermediate, C, species. Their transport is influenced by non-uniformities of water currents resulting from the shoreline topography and river course bathymetry.

The task is to calculate the concentration of chemicals over the river space downstream from the spill site and to identify the locations of high concentration spots of toxic contamination along with the water current distribution.

### Solution method

The GCV method is used to solve the depth averaged conservation equations on 2D BFC computational grid adopted to fit the actual river bed shape where the bottom stresses are calculated by using logarithmic law.

The water flow is supposed to be effectively turbulent not affected by wind stresses. Due to essentially subcritical flow conditions the effect of water surface elevation is not considered.

The main dependent variables are:

• Pressure, P1
• Two components of velocity, U1, V1,
• Mass fraction of pure water, C1 and
• Mass fractions of species, AM, BM, CM, DM and EM.

### Turbulence and chemical reaction models

The model of effective viscosity is used to calculate the turbulent transport properties.

The chemical reaction is presumed to proceed in two stages, viz

• A + B -> C + D, and
• C -> D + E
The reaction rates are assumed to be proportional to the products of component concentrations. The reaction time scales are supposed to be known constants.

### THE RESULTS

The plots show the river geometry, water current field and component concentration contours within river course.

Pictures are as follows :

### THE IMPLEMENTATION

All model settings have been made in VR-Editor of PHOENICS 2002 and the chemical source expressions are implemented via InForm.

The relevant Q1 file can be inspected by clicking here.

svz / jcl