## Fluids

#### Flow Area in 2D Planar Simulation

• Mahdi_171
Subscriber

Hi,

I am changing the pressure at the inlet of a flow between parallel plates and then look at the corresponding volume flowrates. I want to use cfd-post to plot the volume flow rates but the problem is that I am getting different values from fluent and cfd-post using the expression areaInt (u)@inlet and I figured out this happens because the area()@inlet in cfd-post is different than fluent for some reason. Can anyone please show me how to fix this?

• SRP
Subscriber

To fix the issue, you need to ensure that the area selected in CFD-Post matches the area selected in Fluent. Here are the steps you can follow:

1. In Fluent, make sure that the inlet boundary condition is defined correctly with the correct dimensions for the inlet.

2. Check the inlet surface area in Fluent by selecting the inlet surface and looking at the surface area value in the surface integral in the result section

3. In CFD-Post, select the inlet surface and make sure that the surface area matches the value in Fluent.

Can you please share values of area you are getting in fluent and CFD post?

Thank you

• Mahdi_171
Subscriber

Can someone please check this. I still can find an answer to why this added depth appears in cfd-post

• Mahdi_171
Subscriber

I made sure I am selecting the right inlet again in fluent and it is displaying the correct dimensions as in image 1. The distance between the walls is 10um and I am using a reference depth of 1500 um so the area should be 1.5e-8 m^2. In cfd-post the same area is displayed as 1e-12 m^2 in image 2. I thought maybe cfd-post didn't pick the reference depth from fluent but if that is the case then the area should have been 1e-5 m^2 with the default 1m depth. I am not sure why, but it seems like there is a thin depth in the y-z plane that cfd-post added which is causing the wrong area (see image 3) but I am sure my geometry is only a rectangle and the analysis type is 2D. Any idea on what is happening?

• NickFL
Subscriber

CFD Post is the traditional post-processor for the CFX solver. CFX only allows "pseudo" 2D models (one through cell). Because of that, the 2D Fluent results have to be adapted to be read by the 3D CFD Post and that sometimes leads to these weird artifacts.

As for the changing reference depth in Fluent from 1 [m], I would be very careful about doing that. In earlier versions, there were known complications that arose when this was changed off the 1 [m]. Unless you have a reason to change it, leave it alone.

• Mahdi_171
Subscriber

thank you for your response. So it seems like I have to get the flowrate results from Fluent directly in a 2D simulation. As for the depth, I change it because the flowrate values are always per unit depth if set to 1m and it is nice to get the actual flowrate directly from Ansys plots instead of multiplying by the actual depth manually. So far I haven't noticed any complications with changing it (version R21) so It seems like the previous issues are resolved.