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Old   December 8, 2010, 05:45
Default Help: Nasal flow for human
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Chih Fang
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Hello..

Before this i only learnt basic about Fluent and i ran analysis about airfoil both 2d and 3d to obtain Lift and Drag..
However, now i am supposed to run analysis for human nose. And all the settings should be different. But, i have no idea how to do it..

Pls help me.. Thanks..
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Old   December 8, 2010, 17:37
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Julien de Charentenay
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Hi,

I think you are half-way where you want to be. The process is:
- Identify the geometry (human nose, with or without some outside air) and conditions (inspiration, expiration, both in a transient fashion);
- Build the geometry and mesh;
- Set the physical models;
- Set the boundary conditions within your solver of choice;
- Set the numerical parameters, etc;
- Run and analysis.

Personally, I would start simple and refine:
1) do just the nose cavity with a pressure outlet representing the outdoor and a inlet/outlet with a fixed mass flow rate to represent the action of the lungs and limit to either air going in or out (i.e. model a steady-state behavior);
2) Try a transient analysis with the same geometry;
3) Try to expand the analysis by adding a bit of outdoor space and maybe a bit of "ducting" on the other side;
4) Try different models (if applicable).

Hope this help.
Julien
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Old   December 8, 2010, 22:34
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Chih Fang
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Julien, thanks alot.
I already finished with the meshing, its human nose for inspiration.
I set the inlet as mass flow, however i got the info in L/min, but the unit in Fluent is kg/s. I maybe sound stupid, but i dunno how to change it? Do you have any idea?
I think steady state should be ok for me but transient im not sure. Steady state doesnt involve time step rite? Just normal iteration is it?
There are still alot of thing to learn..

Anyway, may i ask personal question? Are you doing the same analysis as well?

Thanks..
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Old   December 9, 2010, 05:21
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Julien de Charentenay
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Hi,

Mass flow (kg/s) = 1.2 (kg/m3) * Mass flow (L/s) / 1000 (L/m3)
(1.2 is the density of air roughly).

Correct, steady-state does not involve time-step, just iterations. But there is no reason to stay away from transient (using fluent, it is just a click of a button away).

No, I don't do simulation of air flow in nasal cavities. I am after buildings and other things (over 10 years experience).

Good luck
Julien

Last edited by julien.decharentenay; December 9, 2010 at 17:28. Reason: Wrong units for conversion L to m3 (formula is correct)
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Old   December 9, 2010, 11:26
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Chih Fang
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Hello,

Thanks alot.. Your replies are really helpful.. Now i will start running the steady state first..
Because i dont really understand about the transient thingy.. Is it opposite to steady state?

Wow.. You have 10 years experience.. Thats amazing..
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Old   December 9, 2010, 17:28
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Julien de Charentenay
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It is amazing I lasted 10 years, indeed...
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Old   December 9, 2010, 17:34
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Julien de Charentenay
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Steady-state: the results assumes that all parameters are maintained in time, therefore the converged solution is "steady-state" (i.e. it will no longer evolve).

Transient: For your scenario, the assumption that someone breathe in (or out) for an infinite period of time is obviously incorrect. So you undertake a transient analysis for a complete breathing cycle (breath in for 2 seconds, pause for 1 seconds, breath out for 2 seconds for example). This would be closer to real life (but also opens lots of questions: what happens if someone breath in for 1 seconds instead of 2? What if I breath slowly first and strongly after? etc). But this analysis is useful to compare to your steady-state analysis and "estimate" the error associated with the steady-state assumption.

There are many other applications of transient analysis, which do not involve time change in boundary conditions: vortex shedding behind a bridge pile...

Hope this help. Julien
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Old   December 9, 2010, 22:31
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Chih Fang
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Haha.. Funny.. Transfer some of your experience to me then.. Need it urgently.. :P

Thanks for your suggestion for transient.. Although not fully understand since i never use the transient analysis before, but it gives me ideas for my future work. Maybe after i finish with the steady state, then i can run transient and compare the results and write a paper about it.
Last time i ran steady state, the results i monitored were the lift and drag. Its very simple setting and all i have to do is get the total lift and drag coefficient. But, for this case, if i wan to get the velocity or pressure at any point along the nose length, how can i get that?
Actually i am taking my masters degree at the moment.. So, i just started getting used to all these softwares. Really thanks for your help..
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