Autodesk Simulation CFD

[#1]

I have a valve that I am simulating in CFD to determine the overall pressure drop.  I first ran the simulation with water and achieved a pressure drop of about 4 psi at 2906 gpm.  In the event that we use oil insted of water, I re-simulated with the SAE hydraulic oil ISO VG 100 and got some strange results.  The pressure drop across the valve was closer to 7 psi.  Considering the specific gravity of both fluids(1 for water and .86 for hydraulic oil, this seems to be an odd result.  I would have expected the pressure drop with oil to be lower than with water.  Can anyone shed some light on this?  Thanks,

Mitch

[#2 · Accepted solution]

The density (SG) is one part of the solution, but you also have to consider the dynamic viscosity.  More directly, the pressure drop is going to be a function of the reynolds number.

What boundary conditions were you using for the analysis?

-Royce

[#3]

Thanks for the response.  I am using water at the default environment settings and a flow rate of 2906 gpm on the inlet.  The outlet is 0 psi.  This is  a 6 inch valve that has 30 inches of inlet pipe modeled as well as a 30 inch outlet pipe.  Will CFD tell me what the reynolds number is?

[#4]

I feel much better about understanding the effect of viscosity now, but I am still wondering about using CFD to determine a reynolds number.  I there any part of CFD that works towards this?  If not I guess I can just work to calculate it from the information used in the CFD.

[#5 · Accepted solution]

Simulation CFD does calculate the inlet and outlet reynolds numbers for you.  You can find these values in the results summary file.  This is located in the 'Review' menu.  Once you have the file open, you want to look at the openings section.

For each opening there will be a reynolds number calculation.

If you want to know the reynolds number someplace else in the model you will have to do that manually.

-Royce

[#6]

Thanks for all your help!