Massflow_rate from Pressure conditions
 

Hi everyone,

I am trying to correlate testing with CFD results of a turbo machinery. In testing they measure only Input pressure and output pressure. I want to know how to calculate massflow rate from any of these two pressures, so that I could use the massflow inlet and pressure outlet conditions in my simulation.

Thanks
Archep:confused:

Why not just use inlet pressure and outlet pressure conditions for your CFD simulation and solve for the mass flow rate?

Hi Michael,

Thank you. I tried it. But when the solution runs, I get messages like " backflow. ... change the boundary condition" .. I haven't done any cfd of internal flows and i find it difficult to understand the phenomena. This is a turbo-machinery problem.

Thanks
Archep

I am no turbo-machinery expert, but you need to get a solution that is stable and at least approximately correct. You can get that either by increasing the pressure difference across the device (start with the largest deltaP you have from the experimental data or even higher) or my fixing the mass flow rate to some sane value, as your first post indicated. If you do the latter with a small mass flow rate, you can then try to scale it up to roughly match your deltaP. In either case, this should allow you to avoid the flow reversals. Once you have a physically reasonable solution established, then you can start walking down the deltaP on your experimental table. If you can't get a reasonable result even with larger deltaP, you may have some other problem in your setup.

Aside from wrong model settings, you may not have enough lead in to your inlet/outlets. If too much flow behavior is occurring near the inlets/outlets, you can get flow reversal. Extending your intake and exhaust pipes may rectify this.

To tell the truth, I do not think you can get what you want only by knowing pressure ... the measurement is for static or total pressure? At the inlet, if you have a measure of both the total and the static pressure, you could use the Bernouille approximation (rough..) and get rho*v^2 ... From the measure of the temperature you can get some other BC.s setting and try to close the problem...

Hi everyone ,

Similar problem ,i am facing only thing is instead of turbo machinery my model is quick response electromagnetic valve.

My boundary conditions are

Inlet pressure - 4 bar
Outlet pressure - atmospheric pressure

Inlet temperature - 295 K
Room Temperature - 305 K

I need to calculate the mass flow rate, velocity and flow through valve.

Of course i am getting the velocity after lot of reversible flow but i need to validate it through the theoretical calculations.

Also mass flow rate is not converging .

Kindly provide your guideliness

Thanks
Ram

Hi Filippo,

They told they are measuring the static and I personally looked at the probe it is placed perpendicular to the direction of flow. Also this probe is at 91mm from the turbine blade.
The model I am using is a simplified model. The inlet is like a shaft where the flow goes in. Its length is 91mm. (Fluid runs this distance, undisturbed before it meets the blades of the turbine). To reduce time, I shortened it to 50mm. Is this a reason for the solver displaying errors like " change to opening boundary". ?