Simple Pressure Drop Calculation
 

Hi everybody,

I am trying to calculate the pressure drop in a simple pipe flow. It is basicly hot air flowing from compressor through a 1,5 meter long pipe which is opening to atmosphere. I have the mass flow rate of the inlet and the ambient pressure (atmosphere). In star ccm+ (i am not very familiar with the software by the way) I choose mass flow inlet as the inlet boundary type and enter the mass flow rate value, I choose the pressure outlet as the outlet boundary type. But the next steps i cannot figure out myself. How should i configure the outlet boundary pressure value and how should i set the initial conditions? Also about creating a report, which report should i creat to see the pressure drop? I really need help on this one.

Hi!
1.) Make two "Surface Average" reports of the pressure at an axial distance X apart.
2.) Search "Referencing Field Functions" and "Using Reports as Field Functions" in help.
3.) Use this technique to make an "Expression Report" which references the field functions that are automatically generated by the Surface Average reports, calculating the pressure drop.
The pressure drop will change with axial distance, as the flow develops. It might be nice to do several seperate pressure drops reports to see how the pressure drop varies with distance from the inlet. If you like, you could reference reports that reference reports to do this!

Hi David,
Thank you for your reply. About the boundaries; should i leave the initial pressure value and reference pressure value for the outlet boundary as they are or how should i set these parameters so that the software reads it as it is an outlet boundary opening to atmosphere? Thanks in advance.

Hi,
Search "Understanding Pressure in STAR-CCM+" for the various pressure definitions, as this will be useful for not only this simulation, but anything else you run! If you set the outlet boundary to "Pressure Outlet", the default setting is 0 Pa "Environmental" pressure, which is what you need for an opening to atmosphere. These questions are all answered in the help documentation, but unfortunately the search function for it is not very practical! I have spent hours going round in loops in the help files!

Thank you very much Dave you've been really helpful.
Cheers.