[Sanu1996]

Hello,

I am doing a steady state anlysis on a centrifugal pump. In my case the impeller(rotor) is completely immersed in the fluid, hence I created the inlet and outlet on the pump (stator). I meshes both stator and impeller (rotor) separately and added them in the CFX setup. I used the interface frozen rotor. In the error message it says the pitch angle ratio doesn't match with area ratio . I have been lagging with this since 2 weeks. Could anyone please tell me the solution to solve this error.

[Stel]

Originally Posted by Sanu1996

Hello,

I am doing a steady state anlysis on a centrifugal pump. In my case the impeller(rotor) is completely immersed in the fluid, hence I created the inlet and outlet on the pump (stator). I meshes both stator and impeller (rotor) separately and added them in the CFX setup. I used the interface frozen rotor. In the error message it says the pitch angle ratio doesn't match with area ratio . I have been lagging with this since 2 weeks. Could anyone please tell me the solution to solve this error.

Do you have 2 interfaces created? One should be at the impeller inlet (side 1 in the stator domain, side 2 in the impeller domain), the other one at the Outlet (side 1 in the impeller domain, side 2 in the stator domain). Also, did you set the pitch change as automatic?

[Sanu1996]

Originally Posted by Stel

Do you have 2 interfaces created? One should be at the impeller inlet (side 1 in the stator domain, side 2 in the impeller domain), the other one at the Outlet (side 1 in the impeller domain, side 2 in the stator domain). Also, did you set the pitch change as automatic?

Hello Stel,
Thanks for your reply. Finally a pitch angle value 360 and topology parameter 2 has solved my problem and the problem is converged. The pressure distribution is very unfamiliar in the post but the output values are matching the experimental values. As you explained I didn't take the side 1 and side2 but I have selected both the sides at a time. Doesn it change the pressure distribution? Can you also tell me the difference between total and static pressure please?

[ghorrocks]

https://en.wikipedia.org/wiki/Total_pressure

https://en.wikipedia.org/wiki/Static_pressure

[Sanu1996]

In my case pump is completely immersed in the tank. So can I say my total pressure is equal to static pressure?

Thanks in advance!

[Stel]

Originally Posted by Sanu1996

I didn't take the side 1 and side2 but I have selected both the sides at a time. Doesn it change the pressure distribution?

Selected both the sides at a time? What do you mean?

Originally Posted by Sanu1996

Can you also tell me the difference between total and static pressure please?

Glenn's links above should help you, but in short, the total pressure is the sum of the static pressure and the dynamic pressure. It is better understood in the context of the Bernoulli's principle along a streamline, but it is relevant in many areas, such as for estimating a pump head, for example.

[Stel]

Originally Posted by Sanu1996

In my case pump is completely immersed in the tank. So can I say my total pressure is equal to static pressure?

Thanks in advance!

No, no direct relationship between one thing and the other. You should be familiar with this concept, it is a basic and important one in fluid mechanics. Again, Glenn's links should help you.

[Sanu1996]

[QUOTE=Stel;781333]Selected both the sides at a time? What do you mean?
I haven't selected both the surfaces separately but selected both in a single interface condition!

[Sanu1996]

Originally Posted by Stel

No, no direct relationship between one thing and the other. You should be familiar with this concept, it is a basic and important one in fluid mechanics. Again, Glenn's links should help you.

Actually I am a structural mechanics engineer, it is first time that I am working on fluids m, so very confused about this. I have considered a boundary condition of Inlet - Total pressure and Outlet - Mass flow as I know both the values from the experimental data. I have seen many tutorials with mass flow inlet and total pressure outlet and still confused about it.

[karachun]

Originally Posted by Sanu1996

I have seen many tutorials with mass flow inlet and total pressure outlet and still confused about it.

I dont know where you see these tutorials but usualy we use mass flow with Static Pressure for incompressible flow.

[Sanu1996]

Originally Posted by karachun

I dont know where you see these tutorials but usualy we use mass flow with Static Pressure for incompressible flow.

Thanks for the reply. I have seen videos on YouTube, ofcourse all of them are not fully reliable. I have used total pressure inlet and relative mass flow rate at outlet (experimentally observed with rotational speed of impeller). I got the value almost equal to experimental when I used total pressure inlet and got a value higher than experimental with status pressure inlet. In the experiment the pump inlet immersed in a fluid. So I am confused if this fluid pressure is static or total.

[Opaque]

Originally Posted by Sanu1996

Actually I am a structural mechanics engineer, it is first time that I am working on fluids m, so very confused about this. I have considered a boundary condition of Inlet - Total pressure and Outlet - Mass flow as I know both the values from the experimental data. I have seen many tutorials with mass flow inlet and total pressure outlet and still confused about it.

I do not recall you can set up ANSYS CFX with a total pressure outlet. Total Pressure boundary condition option is only available for an INLET.

Even for an opening, you may want to read the documentation carefully since the options include an Opening Pressure which behaves as Static Pressure for outflow, and Total Pressure for inflow.

Standard practice for steady flow simulations include:
- Total Pressure inlet + Static Pressure outlet
- Mass Flow Inlet + Static Pressure outlet
- Total Pressure inlet + Mass Flow outlet
- Total Pressure inlet + Exit Corrected Mass Flow (outlet of course)

For transient simulations with incompressible flows, the use of mass flow boundary condition can lead to convergence problems since transient wave propagate too fast and the BC is not flexible enough to change.

Hope the above helps,

[Sanu1996]

Originally Posted by Opaque

I do not recall you can set up ANSYS CFX with a total pressure outlet. Total Pressure boundary condition option is only available for an INLET.

Even for an opening, you may want to read the documentation carefully since the options include an Opening Pressure which behaves as Static Pressure for outflow, and Total Pressure for inflow.

Standard practice for steady flow simulations include:
- Total Pressure inlet + Static Pressure outlet
- Mass Flow Inlet + Static Pressure outlet
- Total Pressure inlet + Mass Flow outlet
- Total Pressure inlet + Exit Corrected Mass Flow (outlet of course)

For transient simulations with incompressible flows, the use of mass flow boundary condition can lead to convergence problems since transient wave propagate too fast and the BC is not flexible enough to change.

Hope the above helps,

Hello Opaque,
Thanks for your detailed reply and it cleared all my doubts bout opening pressure and total, static pressure. Thank ou very much