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Point-velocity of a turbulent flow

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Old   October 11, 2012, 07:30
Default Point-velocity of a turbulent flow
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Liangli
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Dear all:

I am trying something in Fluent which has been bothering me for days.

I have a turbulent flow and some fixed monitoring points. If I plot the velocity as a function of flow time for any of those points I should expect random velocity right? However what I get is a smooth sinusoidal wave. I tried to reduce the time step because I thought maybe because it is time-averaged. I still get the same almost perfect sinusoidal wave.

Is it even possible to capture the velocity fluctuation with fluent or any other CFD programs? If yes, how should I do it? I am really desperate to know. Thanks in advance.
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Old   October 11, 2012, 09:06
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Filippo Maria Denaro
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Quote:
Originally Posted by Meegao View Post
Dear all:

I am trying something in Fluent which has been bothering me for days.

I have a turbulent flow and some fixed monitoring points. If I plot the velocity as a function of flow time for any of those points I should expect random velocity right? However what I get is a smooth sinusoidal wave. I tried to reduce the time step because I thought maybe because it is time-averaged. I still get the same almost perfect sinusoidal wave.

Is it even possible to capture the velocity fluctuation with fluent or any other CFD programs? If yes, how should I do it? I am really desperate to know. Thanks in advance.
first, turbulence is not a pure random signal ... then, what's more is the formulation you are using ... only DNS or LES can give higher statistics, if you use RANS/URANS then you can not see fluctuations over the entire lenghts
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