Pollution and Urban Heating Island (UHI) CFD Simulation
The problem simulates changes in the mass fraction of carbon dioxide on an urban street over time.
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UHI and Pollution CFD Simulation
Urban environments are the most important context of life, and in most developing countries the status of air pollution is getting worse day by day, although technological improvements have played an important role in reducing air pollution emissions. Due to the increasing demand for transportation, it will remain a challenge. Simulation using the Species Transport solves a Transport Equation for each component of the pollution mixture. The purpose of the analysis is to calculate the amount of CO2 pollution dissipated in an urban zone.
UHI Project Description
The problem simulates changes in the mass fraction of carbon dioxide on an urban street. To simulate this model, a 0.1 m height area should be considered as a source of carbon dioxide pollutants on the street from the urban domain. In fact, the main purpose of the current simulation is to investigate the effect of free airflow on the amount of CO2 produced by car exhaust. Therefore, an integrated carbon-dioxide production area is defined as a source of mass production on a city street.
Free airflow enters the area around an urban environment at a velocity of 0.2 m.s-1 and a temperature of 300 K. Since the CO2 and airflow are modeled, the Species Transport model has been used; Thus, these gaseous species include air and CO2. The amount of carbon dioxide produced in the definition area on the street is 4 kg.m-3.
Geometry & Mesh
The present model is three-dimensional and is drawn using the Design Modeler software. This model is a set of structural elements consisting of several building blocks and a street belonging to a city. An area in the shape of a rectangular cube with dimensions of 9 m ⨯ 13 m ⨯ 4 m is designed around this urban complex. The airflow inlet is selected in three lateral sections of this area. There is also a 0.1 m high area on one of the city streets. The following figure shows a view of the geometry.
The meshing is done using ANSYS Meshing software. The mesh type is unstructured and the element number is 4137570. Grids are smaller in the areas adjacent to the internal boundaries and have higher accuracy. The following figure shows a view of the mesh.
Pollution CFD Simulation
To simulate the present model, several assumptions are considered:
- The solver is pressure-based.
- The simulation is transient since the goal is to study changes in carbon dioxide concentration over time.
A summary of the steps for defining the problem and its solution is given in the table:
|near-wall treatment||standard wall function|
|species transport model|
|Boundary conditions (UHI)|
|velocity magnitude||0.2 m.s-1|
|CO2 mass fraction||0|
|gauge pressure||0 Pascal|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|CO2 mass fraction||zero diffusive flux|
|Solution Methods (UHI)|
|turbulent kinetic energy||first-order upwind|
|turbulent dissipation rate||first-order upwind|
At the end of the solution process, two-dimensional contours of pressure, temperature, velocity, air and CO2 mass fraction were obtained in the whole model environment. These two-dimensional contours are drawn in XY and YZ sections. Also, the three-dimensional contours related to pressure, temperature, velocity, air and CO2 mass fraction have been obtained in the area of the CO2 source term.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.