Wind Tower with Qanat, ANSYS Fluent CFD Simulation Training

Description

Introduction

This project is related to a simulation of a wind tower system with qanat using ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.

This system is included in the category of passive ventilation methods. In passive ventilation systems, no mechanical device is involved.

Generally, passive ventilation systems are included in two groups, which are wind-driven and buoyancy-driven. In the wind-driven method, the pressure difference is the factor of air circulation, and in the buoyancy-driven method, the density difference leads to natural convection heat transfer.

The wind tower ventilation system with qanat is placed in the hybrid passive ventilation group (a combination of two groups).

The wind tower system with qanat is one of the traditional ventilation systems based on the architecture of old buildings. This system was very popular in dry and hot areas.

In this system, a tall wind tower is placed on top of the building, and an underground cooling system is considered. In this project, we are using qanat as an example of a common underground cooling system.

When a large structure faces the wind flow, a significant pressure difference appears on its two sides. In front of the structure is a high pressure, and behind it is a pressure vacuum, which leads to air suction caused by the pressure difference.

On the other hand, inside the cooling system or qanat channel, cold water is up to a certain level. The free wind flow enters the channel, and after hitting the water surface, it cools and moistens. This cool air enters the interior of the building from the floor and performs the air conditioning process.

In this problem, the free hot air flow enters the cooling channel with a velocity of 0.2 m/s and a temperature of 300 K. To simplify the problem; we avoided modeling the water level inside the channel and used the constant temperature boundary condition. We assumed that the wall of the underground channel has a constant temperature of 278 K.

We have also modeled some windows on the walls of the room. These windows are exposed to sunlight and in contact with the hot air of the outside environment. So we have assumed that the glass windows have a constant temperature of 298K.

We designed the geometry of the model using Design Modeler software. The current model includes three parts: room, tower and underground channel.

Then we meshed the model using ANSYS Meshing software. The meshing is unstructured, and the number of created cells equals 402198.

Wind Tower Methodology

Using ANSYS Fluent software, we numerically simulated this model according to computational fluid dynamics (CFD). This problem is independent of time and steady state, and the solution is based on the pressure-based solver.

As we said, natural convection heat transfer also happens in this problem. Natural convection is created based on the buoyancy effect. This means that changes in temperature cause changes in density. Warm air is lighter and less dense and rises upwards.

Therefore, the current system is useful for the exit of hot air. The entry of cool air from the floor of the room and the air suction from the exit panel of the tower helps the exit of hot air.

We do not consider the air density constant to apply the buoyancy effect. The relation between density, pressure, and temperature according to the ideal gas law is used in the incompressible ideal gas model. Note that the density is dependent on the operating pressure and is independent of the local relative pressure. So assuming constant pressure, density becomes a function of temperature.

Wind Tower Conclusion

After the simulation, we obtained 2D and 3D temperature, pressure and velocity contours. We also obtained 2D and 3D velocity vectors.

The temperature contour shows well the cooling process inside the room. Cool air enters the underground channel, and hot air exits from the tower panel.

The pressure contour also shows the pressure difference well. The high pressure of the external air and the low pressure inside the room and tower cause hot air to be sucked out.

Velocity vectors show the direction of air movement inside the room and tower well. Cool air enters the room at high speed from the floor, and after full circulation in the room and air conditioning, it leaves through the tower.

So we conclude that we perform the simulation correctly. The passive ventilation system of the wind tower and qanat perform the air conditioning operation correctly.