# BC in rotating machine

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December 27, 2011, 20:11
BC in rotating machine
#1
New Member

Ivan Telnov
Join Date: Dec 2011
Posts: 15
Rep Power: 8
Hi!

I am a student of Kharkiv Politechnical Univ. in Ukraine. Getting master degree i need to study fluent flow in the machine with rotate part (on picture).So I desided to use solidWorks flow simulation 2011.

Geometry is different from centrifugal pumps geometry, that is considered in the video examle. But I think, processes are the same.
I've made 3D-model and i've got some result, but it isn't real. Maybe, there is a problam of Boundary conditions.
What kind of BC it's better to use for solving such study??

thanks in advance
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 model.JPG (58.1 KB, 18 views)

January 9, 2012, 06:17
#2
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Tim Shute
Join Date: Jan 2012
Posts: 9
Rep Power: 8
Hi!

You could read through e example (rotating impeller) in EFD/SW flow simulation turturial that is closely similar to your model and in addition show you how to obtain the pressure drop and efficiency of the impeller. Generally speaking, there are four ways to set up BCs for subsonic simulations:
1. Most robust way: Velocity/Mass Flow at an Inlet; and Static Pressure at an Outlet. The Inlet total pressure is an implicit result of the prediction;
2. Robust: Total Pressure at an Inlet; and Velocity/Mass Flow at an Outlet. The static pressure at the Outlet and the velocity at the Inlet are part of the solution.
3. Sensitive to Initial Guess: Total Pressure at an Inlet; and Static Pressure at an Outlet. The system mass flow is part of the solution.
4. Very Unreliable: Static Pressure at an Inlet; Static Pressure at an Outlet. This combination is not recommended, as the inlet total pressure level and the mass flow are both an implicit result of the prediction (the boundary condition combination is a very weak constraint on the system).

Make sure the openings are long enough to fully develp the flow, otherwise you would be probably prompted if e revolution of the impeller is quite high: warning: a vortex happening at the pressure opening. If not long enough, extent it and you will have a reliable result. I m sure you know what I mean when you look up the pic attached.

Hope useful for you

Tim
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 Vortex happening.jpg (47.5 KB, 22 views)

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