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-   -   How to calculate Turbulent Intensity? (https://www.cfd-online.com/Forums/fluent/39507-how-calculate-turbulent-intensity.html)

 prem February 3, 2006 13:59

How to calculate Turbulent Intensity?

Could any one please guide me on how to calculate the turbulent intensity..While doing k-epsilon turbulent modeling I chose Turbulent Intensity and Hydraulic Diameter Option.Please Help me in this regard.Thanks in Advance

 balmiki February 4, 2006 15:08

Re: How to calculate Turbulent Intensity?

hi prem It is there in Fluent manual. turbulance Intensity = 0.16*{(Re)power(-1/8)} hydraulic dia. for circular section it is equal to diameter of section and for any other section it is sqrt(4*A/pie), where A is area if section . it will be better if u have a look of manual.

 prem February 5, 2006 08:12

Re: How to calculate Turbulent Intensity?

HI balmiki thanks a lot for your guidance

 champshof August 24, 2011 10:39

Quote:
 Originally Posted by balmiki ;128512 hi prem It is there in Fluent manual. turbulance Intensity = 0.16*{(Re)power(-1/8)} hydraulic dia. for circular section it is equal to diameter of section and for any other section it is sqrt(4*A/pie), where A is area if section . it will be better if u have a look of manual.

I know this is an old topic...

But why is the intensity irreversible proportional to the Reynolds number? I would expect that the intensity increases for a higher Reynolds number

 nawar September 11, 2011 21:50

Quote:
 Originally Posted by balmiki ;128512 hi prem It is there in Fluent manual. turbulance Intensity = 0.16*{(Re)power(-1/8)} hydraulic dia. for circular section it is equal to diameter of section and for any other section it is sqrt(4*A/pie), where A is area if section . it will be better if u have a look of manual.
Hi
i want to ask is there any formula for calculating the turbulent intensity of an internal flow in a pipe in the case of non-fully developed flow

i do know how to use the formula of I=0.16〖(Re)〗^(-1/8), but this formula,as i think, can be used only for fully developed flow.

thanks
nawar

 Philipov September 12, 2011 03:32

Fluent manual point two methods for calculating: one for internal flows and one for external....

 Technoyoungman March 4, 2012 09:11

Estimating the turbulence intensity

Estimating the turbulence intensity

When setting boundary conditions for a CFD simulation it is often necessary to estimate the turbulence intensity on the inlets. To do this accurately it is good to have some form of measurements or previous experince to base the estimate on. Here are a few examples of common estimations of the incoming turbulence intensity:
1. High-turbulence case: High-speed flow inside complex geometries like heat-exchangers and flow inside rotating machinery (turbines and compressors). Typically the turbulence intensity is between 5% and 20%
2. Medium-turbulence case: Flow in not-so-complex devices like large pipes, ventilation flows etc. or low speed flows (low Reynolds number). Typically the turbulence intensity is between 1% and 5%
3. Low-turbulence case: Flow originating from a fluid that stands still, like external flow across cars, submarines and aircrafts. Very high-quality wind-tunnels can also reach really low turbulence levels. Typically the turbulence intensity is very low, well below 1%.

 Marli March 4, 2012 15:14

External flow

For 3D external flow around a 3D wheel, bounded by 'parallel' boundaries, what would the boundary conditions for the velocity inlet be in this case? The velocity inlet is 70m/s in my case. (actually simulating the wheel moving at 70m/s, but instead the wheel stationary and the air moving over it). Using the equation previously stated, 'I' comes out at 0.0224 (so 2.24%?). Regarding the second boundary condition, I thought Hydraulic Diameter was not appropriate because the eddies wouldn't be restricted by any boundaries in external flow, so would I used 'Length Scale' as have it has the wheel diameter?
I'm a bit confused as the literature doesn't really define a case like mine.

 Technoyoungman March 21, 2012 14:40

Quote:
 Originally Posted by Marli (Post 347583) For 3D external flow around a 3D wheel, bounded by 'parallel' boundaries, what would the boundary conditions for the velocity inlet be in this case? The velocity inlet is 70m/s in my case. (actually simulating the wheel moving at 70m/s, but instead the wheel stationary and the air moving over it). Using the equation previously stated, 'I' comes out at 0.0224 (so 2.24%?). Regarding the second boundary condition, I thought Hydraulic Diameter was not appropriate because the eddies wouldn't be restricted by any boundaries in external flow, so would I used 'Length Scale' as have it has the wheel diameter? I'm a bit confused as the literature doesn't really define a case like mine.

Yes, there is no literature about turbulent length scale for external flow!!! :(:(:(:(:(

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