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Laminar outflow boundary condition does not converge!
Posted 26 juil. 2013, 05:47 UTC−4 Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4.2a, Version 5.2 2 Replies
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Hello everyone,
I am new to this programm and want to simulate the first part of a streamed circular duct. It serves as an hydrodynamical entry length to develop the velocity flow profile. In the second part (not part of this simulation) the duct is affected by a heat flux to develop the thermal flow profile separately.
Therefore I chose the "laminar flow" physics and used "normal inflow velocity" as a inlet boundary condition. Using "pressure, no viscous stress" as outlet boundary condition COMSOL archieves a solution.
But I want to consider the first part of the duct continued in the earlier explained second part.
So I chose "laminar outflow" as outlet boundary condition with an average velocity=[inflow velocity] (due to unchanged temperature/density) and an exit length=[length of the second part of the circular duct]. Now COMSOL gives the error:
"Failed to find a solution.
Maximum number of Newton iterations reached.
Returned solution is not converged."
Both parts are calculated long enough to serve as an entry/exit length. Re is always <2300.
Please give me a hint about what I did wrong!
Sincerely, Fabian
EDIT: I found out that the max. velocity (2*entry velocity) does not get reached, although the entry length is much longer than 0,056*(Re=2300)*d ?!
I am new to this programm and want to simulate the first part of a streamed circular duct. It serves as an hydrodynamical entry length to develop the velocity flow profile. In the second part (not part of this simulation) the duct is affected by a heat flux to develop the thermal flow profile separately.
Therefore I chose the "laminar flow" physics and used "normal inflow velocity" as a inlet boundary condition. Using "pressure, no viscous stress" as outlet boundary condition COMSOL archieves a solution.
But I want to consider the first part of the duct continued in the earlier explained second part.
So I chose "laminar outflow" as outlet boundary condition with an average velocity=[inflow velocity] (due to unchanged temperature/density) and an exit length=[length of the second part of the circular duct]. Now COMSOL gives the error:
"Failed to find a solution.
Maximum number of Newton iterations reached.
Returned solution is not converged."
Both parts are calculated long enough to serve as an entry/exit length. Re is always <2300.
Please give me a hint about what I did wrong!
Sincerely, Fabian
EDIT: I found out that the max. velocity (2*entry velocity) does not get reached, although the entry length is much longer than 0,056*(Re=2300)*d ?!
2 Replies Last Post 6 août 2017, 06:05 UTC−4
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Posted:
1 decade ago
Hi Fabian,
I think your outlet boundary condition should not define the velocity, since the model already takes care of this with the inlet boundary condition. If you define the velocity at one end, the other end should define the pressure and vice versa.
Best regards
David
I think your outlet boundary condition should not define the velocity, since the model already takes care of this with the inlet boundary condition. If you define the velocity at one end, the other end should define the pressure and vice versa.
Best regards
David
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Posted:
7 years ago
Updated:
7 years ago
i am wondering, how can someone apply velocity gradient [(delu)by del(x) =0] boundary condition at outlet in comsol?