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Initial Values for Laminar Flow

Posted 26.11.2010, 08:30 GMT-5 2 Replies

Matt Kaskow
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I'm having issues with setting inital values. I have a box with a helium inflow on top, and outflow at bottom. Inside there's a small cell. It all works fine, when I set-up these values to proper domains/boundaries:

LF/Fluid prop.
Pressure 1[atm]

LF/Initial Values
Velocity field (0,0,0)
Pressure 1[atm]

LF/Inlet (Laminar Inflow)
Av. Velocity - 1m/s
Lentr - 1m

LF/Outlet
Pressure, no visc. stress - 1[atm],

I plot 3D Arrow volume showing velocity field with flow deformations around the cell. Here's the thing. The target velocity is 30m/s. After I change it to this value, the simulation crashes with information, that consistent inital values cannot be found. I've been changing pressures, entrance length, inital velocity field etc, but I cant find any boundary conditions, that would let me see the results.

Thank You in advance for any tips and hints.
Cheers

2 Replies Last Post 26.11.2010, 09:02 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 26.11.2010, 08:42 GMT-5
Hi

I wounder if it could comes from the numerous pressure definitions you have, pls check carefully as you have relative, gauge and absolute pressures. Test on a simple example that you can calculate analytically.

I would try to define "p" on the initial values and on one inlet or exclusively the outled, only

--
Good luck
Ivar
Hi I wounder if it could comes from the numerous pressure definitions you have, pls check carefully as you have relative, gauge and absolute pressures. Test on a simple example that you can calculate analytically. I would try to define "p" on the initial values and on one inlet or exclusively the outled, only -- Good luck Ivar
Matt Kaskow
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Posted: 1 decade ago 26.11.2010, 09:02 GMT-5
I set up INITIAL PRESSURE to 1E6 Pa, FLUID PROPERTIES/ABS PRESSURE to 110 Pa and OUTLET PRESSURE to 1000 Pa to distinguish which has a greater impact on results. Simulation runs w/o a problem. Thing is, that a 3D Surface with Pressure plot sets value of 1006 Pa at Inlet, and 1000 Pa at Outlet, so it turns out, that Pressure is governed by an outlet pressure? Seems a bit weird to me.

Any ideas?
I set up INITIAL PRESSURE to 1E6 Pa, FLUID PROPERTIES/ABS PRESSURE to 110 Pa and OUTLET PRESSURE to 1000 Pa to distinguish which has a greater impact on results. Simulation runs w/o a problem. Thing is, that a 3D Surface with Pressure plot sets value of 1006 Pa at Inlet, and 1000 Pa at Outlet, so it turns out, that Pressure is governed by an outlet pressure? Seems a bit weird to me. Any ideas?

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