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Physics of an incompressible fluid

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Old   March 23, 2015, 11:14
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Martin Hegedus
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I gather Jonas might not have understood this

"in you room the closed domain does not permit flow to go in/out from walls. Therefore, the fan must be introduced as an external force in the momentum equation to prevent continuity be unsatisfied. This force, if is not divergence-free acts as source term in the elliptic pressure equation."

statement.

Denaro is correct.
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Old   March 23, 2015, 11:26
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Here is the point that people have been trying to make, the fan provides a delta p, it DOES NOT provide a given velocity.

So, in actuality you have assumed a velocity, then calculate the delta p, adjust the velocity, calculate the delta p, and iterate till you are satisfied.
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Old   March 23, 2015, 15:16
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Filippo Maria Denaro
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A fan can be introduced by means of a dp/dtheta gradients in the tangential momentum equation. You can decompose this forcing term along the cartesian direction.

See F. Nygard, H. I. Andersson DNS of swirling turbulent pipe flow, Int. J. Numer. Meth. Fluids 2010; 64:945972
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Old   March 23, 2015, 15:52
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Do you mean dp/dr?

Yes, the torque from the fan must show up in the flow.
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Old   March 23, 2015, 17:09
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Quote:
Originally Posted by Martin Hegedus View Post
Do you mean dp/dr?

Yes, the torque from the fan must show up in the flow.
I don't think torque is relevant. One could imagine a fan with counter-rotating blades, or a grille that straightened the flow.
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Old   March 23, 2015, 17:41
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Yes, put I don't get the impression that is what is being talked about. We're talking about ceiling fans and disk actuator theory.
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Old   March 23, 2015, 17:45
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And yes, if we are modeling the individual blades there will be a dp/dtheta.
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Old   April 22, 2019, 11:40
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Quote:
Originally Posted by Louise Charlton View Post
Sorry, a little lost here but this sounds like a discussion about potential flow (Panel methods, etc.)

No, potential flows share the divergence-free constraint but you can generilize the topic for more general viscous flows
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