Windcatcher CFD Simulation
The Wind Catcher is basically based on the fact that wind is used to draw air into the building and its force response, suction, is used to drive warm and polluted air out.
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Introduction of Wind Catcher and its Mechanism
The Wind Catcher is used to draw air into the building by suction, to drive warm and polluted air out. The internal structure is such that air enters and stuck between the walls. As a result, air moves downward from its outlet valves to the building environment. Windcatcher is a tower for ventilation and cooling of the interior of buildings that locates on the roof of buildings. These windcatchers are usually tall and are made one-way, four-way, and eight-way. The function of the windcatcher is to take the desired wind from ambient to the interior of the building.
Of course, sometimes in the interior of buildings, there are special pools through which the wind flows and cools down by evaporation, resulting in moist and cool winds. In the first view, the wind is used to draw clean and cool air into the interior of the building and its suction is used to expel polluted and hot air inside the building to the outside environment; In this way, when the wind blows to the body at the top of the windcatcher, the pressure increases and due to gravity, it goes down and flows to the interior of the building; While on the other side inside the windcatcher, ie the area behind this body that does not collide with the direct wind flow, it has less pressure than the pressure of the area facing the wind flow, and as a result, the suction of the airflow inside the building upwards.
While the second view of windcatcher performance becomes significant when there is no noticeable wind. During the day, the part of the windshield that is exposed to the sun’s rays causes the air inside it to heat up, resulting in an upward movement, which creates a relative vacuum and, as a result, draws cold air. While at night, the air inside the interior of the building is exposed to heat due to contact with walls with heat stored in it and moves upwards due to lightness, and on the other hand, the airflow the cold air outside is drawn into the interior of the building due to its heaviness.
Windcatcher Project Description
The problem is to simulate the airflow and ventilation inside a windcatcher. The windcatcher is octagonal and has a relatively simple structure. The windcatcher consists of a column for pulling the out air to the inside or sucking up the air inside, room space for air circulation inside it, and a wall for the space around the building of this windcatcher, and also this windcatcher set is located in a large space of open airflow domain. The wind is moving horizontally at a speed of 10 m.s-1 towards the windbreak building. Also, the model pressure is equal to atmospheric pressure.
In the interior space above the windcatcher, surfaces are designed as barriers in such a way that some windcatcher inlets are exposed to direct wind flow; In this way, traction and the suction property is created inside the windcatcher on both sides of the windshield column, and thus the circulation of airflow inside the interior of the room below the windcatcher. The purpose of this project is to investigate the flow of air entering the windcatcher building and the flow of air inside it.
Geometry & Mesh
The present 3-D model is designed using Design Modeler software. The lower part of this windcatcher is an octagonal room with sides of 2 m in length and 2 m in height and has a tower with a height of 8 m. Eight rectangular holes are placed as entrances in the upper area of the windcatcher tower and eight holes as exits in the room below the windshield. A rectangular wall is drawn around the windcatcher. There is also a large outdoor wind area around the windcatcher. The figure below shows a view of the geometry.
The meshing of the model has been done using ANSYS Meshing software and the mesh type is unstructured. In this mesh, the element number is 2332185 and the accuracy of the cells in the areas adjacent to the windcatcher walls is higher. The figure below shows a view of the meshing.
Wind Catcher CFD Simulation Steps
To simulate the present problem, several assumptions are considered:
The simulation is STEADY STATE and the solver PRESSURE_BASED. Also, the effects of the Earth’s gravity on the fluid flow is considered to be -9.81 m.s-1 along the y-axis.
Here is a summary of the steps to define and solve the problem:
|standard wall function||near-wall treatment|
|Boundary conditions (windcatcher)|
|0 Pa||gauge pressure|
|stationary wall||wall motion|
|Solution Methods (windcatcher)|
|Second-order upwind||pressure||Spatial discretization|
|first-order upwind||turbulent kinetic energy|
|first-order upwind||turbulent dissipation rate|
|0 Pa||gauge pressure|
|0 m.s-1||y-velocity, z-velocity|
After the solution process, we obtain the three-dimensional and two-dimensional contours of pressure and velocity, path lines, and velocity vectors.
There is a mesh file in this product. By the way, the Training File presents how to solve the problem and extract all desired results.