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What is a Pressure Point Constraint? When is it used?

Posted 17 oct. 2019, 12:18 UTC−4 Computational Fluid Dynamics (CFD), Microfluidics 1 Reply

shreeyansh96
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My solution is not converging. The model consists of inlet and outlet pressures. I read online in such cases you can use Pressure Point constraint. But I don't know much about it. Can someone help me out in this.

1 Reply Last Post 17 oct. 2019, 13:41 UTC−4
Jeff Hiller COMSOL Employee

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Posted: 5 years ago 17 oct. 2019, 13:41 UTC−4
Updated: 5 years ago 17 oct. 2019, 09:41 UTC−4

The Navier Stokes equation involves the pressure only through its derivatives, so in a NS model you need to specify the pressure at at least one point, otherwise there's an infinite number of solution differing from one another by an arbitrary constant pressure. That's when you want to use the pressure point constraint to fix the pressure at a point.

Since you're imposing the pressure at both the inlet and the outlet, the source of the lack of convergence for your model is different.More likely, there is no solution, or no unique solution, that respects your boundary conditions while satisfying the equation in the domain. It's more typical for inside flow problems to impose the velocity at the inlet and the pressure at the outlet.

Hope this helps,

Jeff

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Jeff Hiller
The Navier Stokes equation involves the pressure only through its derivatives, so in a NS model you need to specify the pressure at at least one point, otherwise there's an infinite number of solution differing from one another by an arbitrary constant pressure. That's when you want to use the pressure point constraint to fix the pressure at a point. Since you're imposing the pressure at both the inlet and the outlet, the source of the lack of convergence for your model is different.More likely, there is no solution, or no unique solution, that respects your boundary conditions while satisfying the equation in the domain. It's more typical for inside flow problems to impose the velocity at the inlet and the pressure at the outlet. Hope this helps, Jeff

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