Smoke Ventilation Using Jet Fan in a Tunnel, CFD Simulation ANSYS Fluent Training

Description

Smoke Ventilation Using Jet Fan Description

Longitudinal ventilation is used, giving the lowest installation and operating cost. The most usual method is to use Jetfoil fans, where the relatively high-velocity discharge induces airflow through the tunnel. As the air from the fan diffuses, it transfers energy to the tunnel airflow and increases static pressure.

Exhaust ducts remove hot gases and smoke produced by the cars and fire from the tunnel volume. In some cases, the extraction capacity may limit the longitudinal velocity in the tunnel under regular operation.

Each tunnel ventilation system uses either tunnel jet fans, large axial fans, or a combination of the two to provide pollution control ventilation and smoke ventilation in a tunnel fire.

Project Description

This project modeled a 3D simulation of a tunnel where several cars move. Hot gases are blowing out the exhaust, and three pairs of fans are placed at the top of the tunnel, abstracting the pollution by a suction.

By making a flow in the fan’s direction, the pollutant (goes up due to lower density than air) moves outside the tunnel.

Geometry & Mesh

The geometry of the solution is a 3D rectangular domain whose length in X and Y and the Z direction is 60m and 10m and 9m, respectively.

Also, there are four cars in different locations of the tunnel. There are three pairs of fans on top of the tunnel at a distance of 25 m.

Design Modeler software is used to create the geometry of the solution.

ANSYS Meshing software is used for generating meshes of the solution. The elements are all tetrahedra. After importing the mesh into the fluent software, the elements are changed to polyhedral because their number decreases significantly.

The number of the elements is precisely 1224231:

The charts below show the quality of the elements.
The elements’ minimum, maximum, and average quality are 5.96e-3, 1, and 0.8190, respectively.

Smoke Ventilation Using Jet Fan CFD Simulation

We consider several assumptions to simulate the present model:

• We perform a pressure-based solver.
• The energy equation is on.
• The present model is steady.
• The effect of gravity is considered.

The following table represents a summary of the defining steps of the problem and its solution:

Smoke Ventilation Using Jet Fan Results & Discussion

At the end of the solution process, two-dimensional contours of pressure, velocity, and volume fractions of pollution and air are obtained. Also, the contours are visible at every five iterations.

The static pressure is visible at different tunnel parts caused by fans.

It also streamlines the pollution blowing out of the exhaust and shows the exact trajectory through the fans.