Boundary conditions for simulation of airflow over buildings

tkc01 · October 29, 2013, 05:02

I am working on a simulation to find out the effect on changing the reflectivity on a roof surface under solar heating from the Sun. I have drawn up a model (cube) where the base is assume to the roof surface.

The height of the cube is 10m, which is my focus in finding the temp distribution up to 10m from the roof surface when I change the reflectivity of the roof surface.

I have define the left face as Velocity input and the right face as outflow.
The front,back and top sides I have defined it as symmetry.

However, I am stuck when it comes to the boundary conditions setting. I understand that I have to use the solar tracing model but for the other boundary conditions, what should I input?

ApoloV · November 22, 2013, 16:24

You would want this model to be a multi part assembly (multiple volumes)

We would want to model the roof as a volume so that we can control its material properties. This would also allow for conduction through the roof to some film coefficient on the interior side of the roof to represent heat loss/gain to the rest of the building.

For the air volume, you may want to have it a bit larger than what you are after and then assign a temperature condition to the lateral sides, the top and the inlet where you have the velocity. The outlet would be a zero pressure without a thermal condition.

October 29, 2013, 05:02	Boundary conditions for simulation of airflow over buildings	#1
tkc01 New Member tkc Join Date: Aug 2013 Posts: 3 Rep Power: 12	I am working on a simulation to find out the effect on changing the reflectivity on a roof surface under solar heating from the Sun. I have drawn up a model (cube) where the base is assume to the roof surface. The height of the cube is 10m, which is my focus in finding the temp distribution up to 10m from the roof surface when I change the reflectivity of the roof surface. I have define the left face as Velocity input and the right face as outflow. The front,back and top sides I have defined it as symmetry. However, I am stuck when it comes to the boundary conditions setting. I understand that I have to use the solar tracing model but for the other boundary conditions, what should I input?

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November 22, 2013, 16:24		#2
ApoloV New Member Apolo Join Date: Jul 2009 Posts: 17 Rep Power: 16	You would want this model to be a multi part assembly (multiple volumes) We would want to model the roof as a volume so that we can control its material properties. This would also allow for conduction through the roof to some film coefficient on the interior side of the roof to represent heat loss/gain to the rest of the building. For the air volume, you may want to have it a bit larger than what you are after and then assign a temperature condition to the lateral sides, the top and the inlet where you have the velocity. The outlet would be a zero pressure without a thermal condition.