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August 16, 2012, 20:09 
plotting u+ vs y+

#1 
Senior Member

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.


August 17, 2012, 18:27 

#2 
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your y+ is too small. Use CFD Online Home > Online tools > Y+ estimation or click on http://www.cfdonline.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) 

August 18, 2012, 09:05 

#3 
Senior Member

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+.


August 18, 2012, 14:36 

#4 
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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 y+ and u+ values with lowRe RANS turbulence models: utility + testcase. You only need to compute u+ with custom functions. 

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