Total pressure drop

[sander.janssens.90]

At this moment I'm trying to simulate an intake of a micro turbine. Due to the fact that there is an orifice at the intake pipe of the turbine, there will be a big total pressure drop. This pressure drop is difficult to measure, so I would like to make an estimation with autodesk cfd. The volumetric flow is known.

When I place next boundry conditions:

- Volumetric flow at inlet: 0.2857 kg/m³

- gauge pressure static: 0 Pa at outlet

I get an increase in  Total pressure instead of a major total pressure drop.

What can be the problem?

Kind regards,

S. 

[OmkarJ]

Contrary to what NS equations predict, it has been documented that in viscous flows, there is a possibility that total pressure may rise locally and this is a result of the redistribution of energy by the viscous stresses. Typically this happens if there is sudden change/conversion of energy is involved, like stagnation point.

The phenomenon is aggravated if 2-eqn models like k-eps are used since they sometimes over-predict the viscosity further aggravating this problem. The modelling assumptions make this situation worse and this is the likelier reason for inconsistencies. 

However, I would first examine if the BCs and mesh distribution are adequate. 

[Royce_adsk]

Are you able to share your model or provide some screenshots?

Thanks,

[sander.janssens.90]

Hi,

I added the files to this message.

It can be that I made some fundamental mistakes because I'm not that familiar with the program (I'm still a graduate student).

But I studied the tutorials and did some research and this is my result.

Kind regards,

S.

[Royce_adsk]

To create this file we need go to the File menu_Save As_Save Share file_Support type.  It will have an extension of .cfz

The file is already compressed, so you do not need to zip it up.  

For future reference to everyone, the .cfdst file has very little use on its own. About the only time I will open it up is if I need to determine if someone is running off a network drive which isn't a good idea.

If the file is too large to attach you could always upload it to your 360.autodesk.com account (similar to dropbox) and provide a public lnk.

Cheers!

[sander.janssens.90]

Thank you for the response. The .CFZ file can be found in the attachment.

Kind regards,

S.

[sander.janssens.90]

Can anyone find a sollution for this problem. I'm still stuck with this.

[Anonymous]

What do you mean with "total"? "Overall" or "total pressure" (static + dynamic pressure). Overall there's a pressure drop as expected... The "total pressure" rises slightly since the velocity rises as well.

I'd refine the mesh anyway and maybe perform this simulation in 2D since it is axisymmetric.

[sander.janssens.90]

Hi Mr. Mueller,

Thank you for the reply. 

I meant the total pressure (static + dynamic). But as I have learned, the static pressure must decrease with increasing speed, because there is no addition of energy and the flow will lose energy due to friction and transformation in turbulent airflow.

http://www.engineeringtoolbox.com/major-loss-ducts-tubes-d_459.html

I will try to make an 2D study, maybe it will simplify things as you said.