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Laminar flow and Heat transfer

Posted Jun 24, 2018, 7:27 a.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD), Mesh 1 Reply

Domi Bede
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Hello guys!

I am facing a problem with Laminar flow and Heat Transfer in Fluids modules. I have found some examples regarding these modules, where in the boundary conditions of the Laminar Flow the "Pressure, no viscous stress" was selected.

For my program, I would like to use in the Boundary Condition section the "Laminar inflow" with a Flow rate given by the user. But in this case, I get the error message "Failed to find consistent initial values".

I have found discussions about this topic: https://www.comsol.com/forum/thread/25297/failed-to-find-consistent-initial-values?last=2017-09-04%2016%3A38%3A20 and I have tried all these suggestions, but none of them worked.

Can somebody help me, how should I put those initial values? I can put some velocity and pressure there, no flow rate.

The final goal is to see the influence of a gas flow in the temperature of a heated body (metallic filament), which is situated in a pipe through which we apply the gas flow.

Thanks for every help!

Domokos

1 Reply Last Post Jun 28, 2018, 9:36 p.m. EDT
Jim Freels mechanical side of nuclear engineering, multiphysics analysis, COMSOL specialist
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Posted: 6 years ago Jun 28, 2018, 9:36 p.m. EDT

A mathematically consistent boundary condition is to set flow at the inlet, and pressure at the outlet. If you all the no viscous stress at the outlet, that is mathematically consistent only if the velocity gradient is zero at the outlet (i.e., no friction). As for temperature, a suggestion would be to set the temperature at the inlet, but certainly somewhere in the domain(s) and/or the heat flux on a boundary. As a user, think of what it takes to solve each individual equation in your system. It gets more complex as you add more equations to you multiple-physics problem.

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James D. Freels, Ph.D., P.E.
A mathematically consistent boundary condition is to set flow at the inlet, and pressure at the outlet. If you all the no viscous stress at the outlet, that is mathematically consistent only if the velocity gradient is zero at the outlet (i.e., no friction). As for temperature, a suggestion would be to set the temperature at the inlet, but certainly somewhere in the domain(s) and/or the heat flux on a boundary. As a user, think of what it takes to solve each individual equation in your system. It gets more complex as you add more equations to you multiple-physics problem.

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