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Mass flow being inadvertedly created

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Old   April 6, 2007, 00:23
Default Mass flow being inadvertedly created
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Daniel
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I'm modelling a pump, with both an impeller and volute to compare both different impellers and volutes before building phyisical models. However, CFX seems to be creating mass between the interface of the impeller and the volute. The volote side of the interface is slightly larger than the impeller side to accomodate for the thickness of the outer surfaces of the volute, and it appears that extra mass is being added in as an effect of this or something of the sort. Is there a way to prevent this?

Thanks, Daniel
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Old   April 6, 2007, 05:08
Default Re: Mass flow being inadvertedly created
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Johnny
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Are you modelling the full 360 of both components, or just a periodic section for the hub? What type of interface are you using between the impeller and volute (frozen rotor, stage?)?

If you have a pitch ratio, then you should expect the mass flows to be different. If the impeller and volute have a mismatch in the spanwise direction, plot the variable Non Overlap Fraction on the interfaces in Post to make sure that the correct sections are being walled off. Mass flow should definitely be conserved across the interface.
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Old   April 6, 2007, 20:19
Default Re: Mass flow being inadvertedly created
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Daniel
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I'm modeling the full 360 degrees of both components. I've tried using both a stage and frozen rotor model for this interface. If by the spanwise direction you mean the radial direction, the two parts were designed so that they should overlap. I'll plot the variable Non Overlap Fraction on the interfaces in post and get back to you
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