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FloEFD/ CHT: How to calculate yplus / y+

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Old   June 14, 2017, 12:06
Default FloEFD/ CHT: How to calculate yplus / y+
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MM
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Hi everyone,

I am a little bit puzzled and hope someone can give me a good hint on this. Currently, I try to simulate a conjugate heat transfer case. Single phase, incompressible, newtonian. However, for evaluating the results, I want to calculate y+ at my heat transfer areas.

I know FloEFD has a special way of dealing with boundarys. There is a Whitepaper where they give values for y+, but in the regular documentation I can find nothing.

Does anyone of you know how to calculate y+ in FloEFD. Is it even possible/ necessary? How can i determine if the resolution on the heat transfer area is good enough.

Thanks for any help.

Regards,
mulm
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Old   December 6, 2017, 17:25
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I'd like to know this too. I wander if Boris knows the answer.
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Old   December 14, 2017, 11:58
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Correct me if I'm wrong but the y+ = u* x y / nu.
With u* being sqrt(tw/rho) with tw being the shear stress at the wall and rho the fluid density.
All parameters do exist in FloEFD so the calculation should be straight forward.

I put the u* as a user defined visualization parameter for this example.
If I select with the probes a specific point on my surface plot and set the u* as the parameter then I get the value for that point. The only parameter missing now it the nu (dynamic viscosity) which FloEFD can also provide with the plot parameter (just might need to activate it from the parameter list) and at your desired location y you can then get the nu and put that into a simple calculator.

You can also use the XY Plot to get the y+ over a longer length of an object for example the length of a flat plate and the same goes for the nu at the specific distance y.
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Old   October 17, 2019, 11:28
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Hello together,

i would like to plot the y+ value on the wall. I searched a time to find these possibilites.

For those of you how are searching the user defined visualization parameter: You can find it in:

Flow Simulation - Tools - Engineering Database

Good Luck!
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Old   October 18, 2019, 04:16
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Yes, it's there where you can specify the parameters to calculate it for a user-defined post-processing parameter.
Simply type in the equation with the selection of the parameters from the drop-down list.

It should also work if you copy past the equation below into the equation field:
{Wall Distance}*({Shear Stress}*{Density (Fluid)})^0.5/{Dynamic Viscosity}

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Boris
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Old   October 18, 2019, 04:27
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Thanks again Boris.

One small error is in your Formula.

Ny is the kinematic viscosity.
Eta the dynamic viscosity.

Ny=eta/rho

-->

{Density (Fluid)}*{Wall Distance}*({Shear Stress}*{Density (Fluid)})^0.5/{Dynamic Viscosity}


Best regards. I am glad to find such a fast help in you!
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Old   October 18, 2019, 04:30
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Yes, you are right. Sorry, I picked the first viscosity I found.

Boris
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conjugate heat transfer, floefd, heat transfer, yplus

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