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Rotating Region, inlet outlet mass flow dont match (No conservation of mass)

Question asked by Andrew Locker on Jul 4, 2019

I am struggling with a time dependent, rotating region (sliding mesh) simulation.

I am running a simulation for a regenerative turbine pump (peripheral pump). [do a quick search if you arent familiar]

The working fluid is water. The size of my rotating region is the exact same size as my impeller.

I cannot seems to get the inlet and outlet volume flow rates (or mass flow rates) to equal each other in this pump.

These numbers can be way off throughout the simulation solution. I dont understand how the software could produce this result. The inlet and outlet mass flow rates have to equal eachother.

I have run many many centrifugal pump simulations and have never had this issue.

This is my forst time trying this type of pump. (regenerative turbine)

I will occasionally get warnings (negative pressure or vortex accross BC), but often there are no warnings and the inlet and outlet volume flow rates and mass flow rates can be off by an order of magnitude (or even worse, sometimes they will both be positive or both negative)

This just shouldnt even be possible for flow simulation to produce these results.

I have pressure, volume flow rate, and mass flow rate goals on inlet and outlet.

I have torque goal on impeller.

 

[Things I have tried Already]

- Changing BCs (Inlet flow-outlet pressure, inlet pressure-outlet pressure, inlet flow-outlet flow)

-increasing mesh density in general and specifically near the inlet and outlet boundary conditions.

-lengthened the inlet and outlet tubes.

-I have tried alternate models with single piece volutes to make sure there wasn't somehow a leak that wasn't detected.

-I checked for leaks on various different model configurations and there aren't any.

-I have tried various geometric spacing values between the impeller front, back, and outer diameter and the volute. (ie larger impeller tip clearance, etc.)

 

 

Here is the assembly.

 

Here is the impeller itself.

 

EDITED BY MODERATOR: Moved to the Flow Simulation sub-space. Please post in the appropriate sub-space if one exists.

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