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Blooper
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Vortex Shedding Question

04/05/2016 10:05 AM

hi guys!

looking for an answer : why in CFD ,we choose to plot the lift force coefficient instead of plotting the lift force (flow around a cylinder in solidworks)?

need a detailed explanation ! thank you.
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Rixter
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#1

Re: vortex shedding question

04/05/2016 10:24 AM

Maybe the lift force coefficient is independent of flow rate whereas lift force is not?

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phoenix911
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#3
In reply to #1

Re: vortex shedding question

04/05/2016 10:38 AM

that's pretty detailed with the information given.

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Blooper
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#9
In reply to #3

Re: vortex shedding question

04/05/2016 11:42 AM

what do you need?
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phoenix911
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#10
In reply to #9

Re: vortex shedding question

04/05/2016 11:48 AM

Actually the question is what do you need...

Vortex shedding is can create havoc that can have a number of variables that is impossible for us to guess.

Flow induced vibration problem in a cross flow tube bundle heat

.

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TonyS
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#2

Re: vortex shedding question

04/05/2016 10:24 AM

We need a detailed explanation as to why you haven't done your homework.

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Blooper
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#6
In reply to #2

Re: vortex shedding question

04/05/2016 11:35 AM

what do you mean!
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PWSlack
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#7
In reply to #6

Re: vortex shedding question

04/05/2016 11:38 AM

Given that the question indicates plural [N] persons, the reason for coming to CR4 instead of asking one of the N-1 other people involved is abstruse.

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SolarEagle
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#4

Re: Vortex Shedding Question

04/05/2016 11:22 AM

http://slideplayer.com/slide/2523747/

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Blooper
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#11
In reply to #4

Re: Vortex Shedding Question

04/05/2016 12:15 PM

what about the lift coefficient!!!!!!!!!!!!!!!!!!!
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SolarEagle
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#13
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Re: Vortex Shedding Question

04/05/2016 2:58 PM

Lift force is always relative to the fluid density and velocity on the surface area of the object.... These we would refer to as the various complexities....

"The lift coefficient (CL, CN or Cz) is a dimensionless coefficient that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area. "

We can then use this coefficient as a statement of the force in these circumstances, and make change calculations that are relative to this known existing force that has been proven in these circumstances and conditions...otherwise yer just flyin' blind..

https://en.wikipedia.org/wiki/Lift_(force)

https://en.wikipedia.org/wiki/Lift_coefficient

https://www.grc.nasa.gov/www/k-12/airplane/dragco.html

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Blooper
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#14
In reply to #13

Re: Vortex Shedding Question

04/05/2016 5:23 PM

so if i'm gettting it right, beeing dimensionless makes it a good tool to evaluate the behaviour of the fluid (around a bluff body) but is there a way or a formula to proof that the calculated vortex shedding frequency by CFD (using the lift force coefficient) is the same as the lift force's, thanx pale.
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SolarEagle
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#15
In reply to #14

Re: Vortex Shedding Question

04/05/2016 9:25 PM

http://www.cfd-online.com/Forums/main/80134-vortex-shedding-frequency.html

https://www.grc.nasa.gov/www/k-12/airplane/lifteq.html

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Blooper
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#18
In reply to #15

Re: Vortex Shedding Question

04/06/2016 9:06 AM

thank you so mutch it was realy ,helpful!

happy to know you!
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Codemaster
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#19
In reply to #4

Re: Vortex Shedding Question

04/07/2016 5:18 AM

Interesting chart, I'll save that. But what is BL?

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SolarEagle
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#21
In reply to #19

Re: Vortex Shedding Question

04/07/2016 6:36 PM

I believe that would be boundary layer....

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#20
In reply to #4

Re: Vortex Shedding Question

04/07/2016 2:19 PM

A minor point, but it might confuse some readers - it should say Fdrag = Cd*1/2*ρ*U2*A where U = fluid velocity. ν (nu, but it doesn't come out too well on here) is kinematic viscosity, in Reynold's No. R = U*D/ν. As I'm sure you know!

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SolarEagle
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#22
In reply to #20

Re: Vortex Shedding Question

04/07/2016 6:46 PM

https://www.quora.com/What-is-the-difference-between-dynamic-and-kinematic-viscosity

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Codemaster
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#23
In reply to #22

Re: Vortex Shedding Question

04/08/2016 6:46 AM

Yes, I know kinematic viscosity ν = dynamic viscosity μ/ρ, density (not specific gravity BTW).

I was just pointing out that ν in the formula for Fdrag is wrong. A typo I assume, not yours, in the original, or just mixing up ν (nu) with v or V for velocity. Though on the graph velocity is U.

Thanks for the BL.

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#5

Re: Vortex Shedding Question

04/05/2016 11:27 AM

<...we choose...> Simply ask the rest of <...we...>. This forum does not know to whom the word <...we...> refers.

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Blooper
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#8
In reply to #5

Re: Vortex Shedding Question

04/05/2016 11:39 AM

ok english man!
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Blooper
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#12

Re: Vortex Shedding Question

04/05/2016 12:28 PM

is there a better answer !
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lyn
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#16
In reply to #12

Re: Vortex Shedding Question

04/05/2016 10:50 PM

Why not propose some answers that you have discovered first.

Where have you looked, so far?

Do you have a text book?
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IdeaSmith
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#17
In reply to #12

Re: Vortex Shedding Question

04/05/2016 11:04 PM

If you find out let us know?

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