Autodesk Simulation CFD

[#1]

I have set up a model to simulate airflow through a canopied generator set.

The model is very simple with a fan pulling airflow through inlet ducts, over an engine, through a cooling core and out a 90 Degrees vertical outlet duct at the top of the canopy.

The geometry has been set up with 0 gage pressure only as a boundary condition, the fan has a fan curve from the supplier and the cooling core has an air restriction curve from the supplier.

I am looking to run an accurate model as possible but due to computational restraints, cubes represent engines etc.

The outcome I am looking for is a pressure restriction of the canopy and a volumetric flow at the outlet.

I know there is a summary report, but is there a way to set up a plane to show volumetric flow at the outlet? Or the pressure drop through the system?

Also, I know increasing meshing size will help accuracy of the model, but is there any other tips/help more experienced users can offer to better setup this model. For example, does setting a free air ratio as a resistance instead of a restriction curve better represent reality within Autodesk Simulation?

Thanks in advance

[#2]

Hi,

Sounds like you have the right approach, there are a few things to mention that might help:

1. Suppress all solid parts from the mesh if you are not interested in heat transfer though them, this will save on mesh count
2. A resistive region should be accurate with either approach, so long as whatever you assign matches reality
3. You need a good uniform mesh on resistance regions and fans, aim for at least 4 elements through their thickness
4. You can measure flow or pressure on planes by addingn a cut-plane and using the bulk calculator - search the help and use the Wiki if you need more detail, it explains it all well.

[#3]

Thanks Mr. Wilde,

Does suppressing solid parts just stop heat transfer through them? Do they not have to be meshed for the CFD program to ascertain aiflow patterns around/ past/over solid objects?

Would this mean the only meshing I would be applying would be to the fan and the cooling core?

If I am modelling a fan, is ther any rules of thumb for the modelling? Currently I am using a cylinder, with no inner fixed hub modelled. It is set to the thickness of the suppliers drawing from one side of a blade tip to the other.

I feel I will have to play about with the resistive regions,  at the moment I have a grill outlet setup as a pattern from the model which is creating alot of nodes. I think it might be better to set this as a resistive region with a free air ratio.

Thanks.

[#4]

Not a problem

Does suppressing solid parts just stop heat transfer through them? Do they not have to be meshed for the CFD program to ascertain aiflow patterns around/ past/over solid objects? You are correct, it will just stop the heat transfer, the flow patterns around them would not be affected.

Would this mean the only meshing I would be applying would be to the fan and the cooling core? And the air, yes.

If I am modelling a fan, is ther any rules of thumb for the modelling? Currently I am using a cylinder, with no inner fixed hub modelled. It is set to the thickness of the suppliers drawing from one side of a blade tip to the other. What you have souds sensible, although it is worth including a solid part around the outer diameter to ensure that no flow can leak. also ensure it has a good uniform mesh.

I feel I will have to play about with the resistive regions,  at the moment I have a grill outlet setup as a pattern from the model which is creating alot of nodes. I think it might be better to set this as a resistive region with a free air ratio Yes, this might be worthwhile. You can set the resistance to be different in each of the x.y,z directions to try to mimic the grill pattern.

[#5]

Hi,

Many thanks for the reply.

I just have a couple more questions.

1. When I am modelling the fan, is it better to have a solid cylinder in the center to represent the hub? I have set a solid exterior to stop flow leak.

2. I have set up  the geometry as a 0 Pa gage pressure. Is there any need to specify inlets as 0 Pa gage pressure as well?

Thanks in advance.

[#6]

1. When I am modelling the fan, is it better to have a solid cylinder in the center to represent the hub? I have set a solid exterior to stop flow leak - It does not really matter althuogh you can do - suppress it from the mesh if you do.

2. I have set up  the geometry as a 0 Pa gage pressure. Is there any need to specify inlets as 0 Pa gage pressure as well - I am unsure what this means. You only want to assign a p=0 to the fluid where there is an opening and only on the boundary of the model - nothing internally 

Does that make sense?

Thanks,

Jon