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-   -   plotting u+ vs y+ (http://www.cfd-online.com/Forums/fluent/106057-plotting-u-vs-y.html)

 Shamoon Jamshed August 16, 2012 20:09

plotting u+ vs y+

I want to plot the famous TBL curve U+ vs y+on an aerofoil at supersonic speed. M=2. for potting U+ vs y+ I drew a vertical line in the mid chord, sufficiently enough to be in the boundary layer as I see through vector plot. I calculated U+ via formula through custom f/n from U/utau. and utau=sqrt(shear stress/density). When i use wall shear stress option in available functions of Fluent the U+ value was computed to be zero. Then I used tau=mu * (du / dy)y=0. This gave me some value but I still don't get the TBL plot. I get y+ value from 0.01 to 0.6 in the plot as well as maximum in the contour plot range. When I use the log scale it says that no data points in range. Please help me in this regard.

 Touré August 17, 2012 18:27

your y+ is too small. Use CFD Online Home -> Online tools -> Y+ estimation or click on http://www.cfd-online.com/Tools/yplus.php
Estimated wall distance is y with this tool.
Y+ for the cell adjacent to the wall is between is 1 for enhenced or 30 for standard turbulent model (See documentation)

 Shamoon Jamshed August 18, 2012 09:05

The thing is that y+ is although very small but I want to plot the famous curve of U+ and y+ which I dont get. Forget that my y+ is 0.6 lets assume it is 1 then how can I plot U+ and Y+.

 Touré August 18, 2012 14:36

Check the document at page 19 http://www.stanford.edu/class/me469b...turbulence.pdf
y+ begins in the diagram with 1. I don't think that y+ is defined under this value of 1.

There is a thread for how to compute y+ (FLUENT: variable -. Turbulence -> wall y+) and u+ at http://www.cfd-online.com/Forums/ope...-testcase.html.
You only need to compute u+ with custom functions.

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