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Old   November 14, 2003, 06:15
Default Y-Plus
  #1
Florian
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hi everybody, i am trying to simulate the surface temperature of a coupling enclosure. thus the heat comes from a rotating coupling (14000 rpm) and now my question is, do i have to use the reynold stress model and which value of Y+ should i have or is it enough when i am only using the k-epsilon turbulence model? what are the values of Y+ for the k-epsilon model? thanks, Florian
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Old   November 24, 2003, 00:32
Default Re: Y-Plus
  #2
KKA
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which k-epsilon models do you want to use? high or low-Reynolds number. for high reynolds number: y+ >= 20 and for low-reynolds y+ =< 2.

CFX/CFX-TASCflow guys recommend to use k-omega instead of low-reynolds number model for k-epsilon.

all the best! Check the User manual. email me!
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Old   November 25, 2003, 04:30
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  #3
Florian
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thanks for your help. now i switched to the sst-model with automatic wall function and with a value of about 100 for y+, that works quite good when i´m using the k-epsilon model for the first 100 iterations.
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Old   November 25, 2003, 05:32
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Jan Rusås
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The SST model with a Y+ on 100? I had the impression that the SST was a modified k-omega model, which basically means that Y+ should be small also with the scaled wall model ?? Any opinion?
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Old   November 25, 2003, 05:43
Default Re: Y-Plus
  #5
Florian
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thats right, the sst model is a mix of k-omega and k-epsilon. in near wall regions the k-omega model is used and in the middle the k-epsilon which can be seen when plotting the first blending factor where 1 means k-omega and 0 for k-epsilon. I have read in an article on the cfx homepage that for sst model and automatic wall function any value for y+ between 2 and about 100 can be used, there will always be the same solution.
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