Description

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 mixture. The purpose of the analysis is to calculate the amount of CO2 pollution.

Geometry & Mesh

We design the 3-D urban zone by Design Modeler software. After modeling the geometry, it is time to move on to the next step, Meshing. Since the ANSYS Fluent software uses the finite volume method, it is important to have a high quality grid.

The mesh should have two main features:
1. In areas where there are high variations (steep gradients), grid should be small enough.
2. The boundary layer meshing should be properly done.

Due to the geometrical complexity, it was not possible to have an structured mesh, so the unstructured mesh was done. The total element number is 3,416,951. Since the mesh was not sufficiently fine-grained, Wall-Function was used to estimate the boundary layer.

Pollution Analysis by ANSYS Fluent software

Once the mesh is loaded onto the ANSYS Fluent software, the solution process begins. The following steps must be done:

1. Definition of the problem
2. Select the turbulence model
3. Define cell zone and boundary conditions
4. Activate the Species Transport model
5. Definition of materials
6. Determine how to solve the equations and specify the quantities to solve

Solver settings:
Type:	Pressure-based
Velocity formulation:	Absolute
Time setting:	Steady State
Energy:	On
Model:	k-epsilon standard
Near-Wall treatment:	Standard Wall function

Boundary conditions:	Inlet : velocity inlet : 0.2 m/s | 0      CO2 mass fraction Outlet : pressure outlet : 0 pa | 0      CO2 mass fraction Wall-road : No-slip                | 0.02 CO2 mass fraction symmetry : Symmetry City Streets : Wall : No-slip   | 0.02 CO2 mass fraction Building : Wall : No-slip        | Zero Diffuse flux CO2
Solution methods:	SIMPLE
Pressure interpolation scheme:	Standard treatment
Momentum:	Second Order Upwind
Turbulent kinetic:	First Order Upwind
Turbulent dissipation:	First Order Upwind
Species Transport :
Species Transport :	Enabled
Options:	Diffusion Energy Source
Number of volumetric species:	2
Initialize:	Hybrid
Residual Tolerance:	9e-4
Material used :
Mixture:	CO2 : Cp piece-wise polynomial Air  : Fluent Default

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.