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Abnormal pressure comparing to Fluent

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Old   November 26, 2013, 23:45
Default Abnormal pressure comparing to Fluent
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I am simulating a pipe flow with cavitation physics. The inlets and outlets cannot be defined as pressure conditions according to the current available data. Mass flow rate at the inlet and continuity at the outlet are in use. The solver will report "there is no reference pressure available".

When using velocity inlet and outflow outlet conditions both in fluent and flow3d, the results are quite different. The range in Flow3D is wider and the value is much larger.

How to make the two results with the same value within an acceptable discrepancy.

Is there a possible way to define the reference pressure without defining the pressure boundary conditions? Void pressure does not work.

Thanks if there is any help.
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Old   December 3, 2013, 13:06
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Jeff Burnham
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You should not use cavitation physics without a reference pressure. Cavitation occurs at a cavitation pressure which must be known. If the "available data" doesn't provide upstream pressure, then there is not enough data to model cavitation.

If you know the flow rate, then use Bernoulli's equation to determine the difference between inlet and outlet pressures to get that flow rate. Set the pressure boundaries to 'static' type, that is, uncheck the 'stagnation' box. 'Static' works well for confined pipe flow, but is not recommended for free-surface upstream boundaries.

Also, make sure that the cell sizes and time steps are identical between the two software models. It is not appropriate to compare softwares unless the discretizations are also the same: the "error" between software could be due to different cell sizes or time steps, and not due to differences in solution method.
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