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Author Topic: Tangential Velocity  (Read 8113 times)

nsdmr

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Tangential Velocity
« on: May 07, 2013, 08:30:41 am »

Hello pyrosim users,

I hope this question hasn't asked before, how you manage a tangential velocity? I want to create a 60 degree angled fan for ex. Could this be possible? I've attached a picture of my project which has some fans blowing the air in x,y,z directions. I want to blow the air through the escape routes for two circled fans . But they blow the air through the red lines not black ones. If their velocity would be 5 m/s, what i should apply for tangential velocity? assume the angle about 30 degrees.

Please help.
Thanks.
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Charlie Thornton

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Re: Tangential Velocity
« Reply #1 on: May 08, 2013, 08:52:10 am »

The details are in the FDS Users Guide, Section 9.1.4 "Louvered Vents". You have to work out what you need the tangential component of the velocity (in your case X or Y - the left box in pyrosim) to be to achieve your 60 degree angle.
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nsdmr

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Re: Tangential Velocity
« Reply #2 on: May 09, 2013, 12:25:08 am »

yes, i read it but i don't understand the logic. is there any formula about this description. i want to create a velocity with 60 degree angle but there is no further information in fds manual

note: the problem is not about mesh resolution (it's 0.1X0.1X0.1).
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Charlie Thornton

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Re: Tangential Velocity
« Reply #3 on: May 09, 2013, 08:52:09 am »

Here is my unofficial, barely-tested derivation.
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nsdmr

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Re: Tangential Velocity
« Reply #4 on: May 10, 2013, 05:14:01 am »

i see your approach but it doesnt work properly in pyrosim+fds. for example i want a velocity with 15.555 m/s and 7 degree angle. according to your derivation, V_T must be 1.70105 m/s however when i put normal velocity about 15.555 m/s and tangential velocity about 1.70105 m/s, average velocity becomes 9.5 m/s and angle becomes very different from 7 degree.

on the otherhand, these all were for supply surface. but when i use fan surface and apply it to thin obs. also, i different phenomenon occurs. if the fan surface is very close vertically to ceiling, there is a coanda effect and the fan blows toward to ceiling. how can i solve this problem. any idea...

note: the problem is not about mesh resolution (it's 0.1X0.1X0.1).
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Charlie Thornton

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Re: Tangential Velocity
« Reply #5 on: May 10, 2013, 09:34:29 am »

My understanding was that VEL was the velocity independent of direction and the VEL_T components changed the direction but not the magnitude.

I'll do some tests and get back to you.
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Charlie Thornton

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Re: Tangential Velocity
« Reply #6 on: May 13, 2013, 02:07:50 pm »

When I set VEL=15.555 m/s and VEL_T=[1.70105, 0.0] on a supply vent, I get the expected result of a 7 degree angle with a strength of a about 15 m/s. I'm not sure what we are doing differently. I'm using FDS 5.5.3

Here is a picture of my result and my PSM file.
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nsdmr

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Re: Tangential Velocity
« Reply #7 on: May 15, 2013, 04:58:24 am »

Yes, that's exactly what we did, but it does not work sufficiently with fan surfaces just with supply vents.
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Charlie Thornton

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Re: Tangential Velocity
« Reply #8 on: May 15, 2013, 09:07:09 am »

Thank you. I missed the distinction that we are talking about a PyroSim FAN type. There may be a limitation in FDS or in the way PyroSim generates the input file when it comes to using SURF's POROUS option. In FDS User Guide Section 9.1.5 "Jet Fans", the manual seems to assume axis-aligned flow. I'll check it out.
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nsdmr

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Re: Tangential Velocity
« Reply #9 on: May 17, 2013, 12:57:42 am »

 i think true derivation is vel_t= vel_normal*tan(a)     
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