[CFD] What is the difference between y+ and y*?

A concise explanation of the difference between the dimensionless wall distances y+ and y*. These metrics are used by all mainstream CFD codes (OpenFOAM, CFX, FLUENT, Star, Saturne, COMSOL). The following topics are covered:

1) 7:36 What is the difference between y+ and y*?

2) 10:22 Is it better to use y+ and y*?

3) 17:54 Which CFD codes y+ and which CFD codes use y*?

#yPlus #fluidmechanics101 #cfd

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Some useful references:
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1) ANSYS FLUENT User Manual
12.10.2 Standard Wall Functions

2) J. Bredberg, On the Wall Boundary Condition for Turbulence Models, Internal Report 00/4, Chalmers University of Technology, Goteborg, Sweden, 2000.

3) R. Moser, J. Kim and N. Mansour. Direct numerical simulation of turbulent channel flow up to Re_tau = 590. Physics of Fluids, 11(4):943-945, 1999.

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Disclaimer
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The methods, algorithms, equations, formulae, diagrams and explanations in this talk are for educational and demonstrative purposes only. They should never be used to analyse, design, accredit or validate real scientific / engineering / mathematical structures and flow systems. For such applications, appropriate trained, qualified and accredited (SQEP) engineers / scientists should be consulted along with the appropriate documentation, procedures and engineering standards. Furthermore, the information contained within this talk has not been verified, peer reviewed or checked in any way and is likely to contain several errors. It is therefore not appropriate to use this talk itself (or any of the algorithms, equations, formulae, diagrams and explanations contained within this talk) as an academic or technical reference. The reader should consult the original references and follow the verification and validation processes adopted by your company / institution when carrying out engineering calculations and analyses. Fluid Mechanics 101 and Dr. Aidan Wimshurst are not accountable or liable in any form for the use or misuse of the information contained in this talk beyond the specific educational and demonstrative purposes for which it was intended.

[awos]

Everyone saying thanks, meanwhile I just hit Y and missed enter xd

[noahzhang]

Finally, there is someone doing this kind of in-depth explanations of those parameters we use in the simulation. Well done!

[thekoseng]

i was searching for youtube but accidently typed y+, but nice video 👍

[hydrokbar]

thanks a lot dear dr. aiden. it is impossible to find these materials as easy as here. I appreciate

[sreekar]

You upload exactly when I'm searching for it. Great explanation mate

[谢岸峰-zl]

Very explanatory video helping me a lot while getting through CFD literatures. Thanks a lot!

[mdfaiazkhaled]

Once again. A brilliant and articulate lecture.

[rohanverma]

Hello sir, thank you for uploading this. Its very informative because I was always confused in this topic. Please keep posting the vedio like this on CFD.

[MultiMartini]

I really love your lectures, it is a great help in understanding CFD codes/models

[riccardocolombo]

I love your contents, many thanks from PoliMi ! 🇮🇹

[teddya]

Thank you for the explanation. Very helpful for me who is learning CFD.

[medusillaycalamar]

Thank you man =) Great video! Precise and concise

[prasisgod]

Brilliant upload. Exactly what I was looking for!

[nightwalker]

Thanks for the video, very clear explanation indeed.

[minhn]

Hello, this is a wonderful video, but I have a quick question, regarding a point made at 10:10. How can y+ and y* (assuming you're in an equilibrium turbulent boundary layer) end up being the same, when tau_w, as a measure of shear stress, is a value that is independent of wherever your y is, whereas turbulent kinetic energy k_p is going to necessarily change depending on your distance from the wall?

[anupamdas]

Dr Aiden, can you please make a video explaining Two-Layer Model for Enhanced Wall

[Yiqingzhang-vncr]

I would like to ask you, how to calculate the characteristic length of open channel flow?Y+ needs to be calculated when drawing the grid, so the value of the feature length needs to be known. I want to know whether the feature length of open channel flow is calculated by hydraulic radius or hydraulic diameter? Can you give specific formulas for reference?

[akbarravan]

Hello Dr. Aidan. Thanks for these great contents.

I completely understood how y+ is being calculated. I justed wanted to ask why we used the the log-law profile for calculating tau_w in Equation 6, andthen deriving Equation 7? In low-Re simulations, the first cell is not in the log-region. Is the explained procedure only works for high-Re simulations?

Thanks in advance

[niki]

I always end up here when I want to type "y" in my search bar to get to youtube but mistype and end up typing "y+"

[hernanjaviergomezzambrano]

¿Cómo se calcula el valor de la energía cinética turbulenta (k), si aun no se tiene valores para iniciar?... How do you calculate the value of the turbulent kinetic energy (k), if you do not yet have values ​​to start with?