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Setting Boundary Condition for Transient Navier Stokes

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Hi all!

SETTING BOUNDARY CONDITION FOR TRANSIENT NAVIER STOKES

I want to set a boundary (i.e. inlet) with constant flow rate of 1.11 m/s.

In "Constant" option, I have set

u_in = 1.11 [m/s]

However, I cannot get initial value with the solver. I need the initial value (at t=0) for the transient solver to begin.

In the second case, I tried setting the flow rate at

u0 = 1.11*(t[1/s])

The transient solver (i.e. BiCGStab) could give a solution but the velocity is increasing with time and this is not what I want.

Basically, my case is very simple. A step increase of constant magnitude (i.e. constant velocity). How should I set me boundary condition in order for the solver to be able to obtain constant inlet flow?

Please help me! Thank you very much!

1 Reply Last Post 2010年1月15日 GMT-5 02:50
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 2010年1月15日 GMT-5 02:50
Hi

if you want to study th step, I wouuld trie one of the "heaviside" functions to make a short but smooth step, this helps the solvers to follow the non-linearities
Good lukc
Ivar
Hi if you want to study th step, I wouuld trie one of the "heaviside" functions to make a short but smooth step, this helps the solvers to follow the non-linearities Good lukc Ivar

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