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Old   January 24, 2006, 15:48
Default y+
  #1
Drauss
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hello

i have been using the y+ calculator here for a while; i like to ask two questions:

1)does anyone knows the equations inside of the y+ calculator; i do know the text book equation but the y+ calculator asks only for Reynold, ref length and y+. i just want to build my own on excel!!

2) also for a 3-D problem of plate (ex: the floor of a room 7 x 7 m), is it okay to take the ref length as 7 m?? is 7 m a good number for any points along the floor (plate)??

3) is it acceptable to the establish grid independence by performing several computation at different first grid distance. then at the moment the results at one point does not change anymore. Take that first grid distance as the correct grid distance from the wall????? this way no need for y+
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Old   January 24, 2006, 15:51
Default Re: y+
  #2
Drauss
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sorry forgot to ask the last question:

why is that for Reynold less than 10-5, the y+ calculator does not compute anything?

many thanks and happy new year
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Old   January 27, 2006, 03:58
Default about convergence
  #3
Rameshwari
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hi I am doing problem of rapid mixing tank in water treatment plant. while running tank in fluent all five element i.e. is x,y,z,k,epsilon is converged but continuity is not converged what is reason i have not understand please help me for that.....
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Old   January 28, 2006, 02:39
Default Re: y+
  #4
Omar Qazi
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About the question regarding y+. I guess you have to resolve y+ to the required level inorder to resolve the turbulrnt boundary layer characteristics. Generally, the code will switch over automatically to near wall-modelling if you have a y+ of higher that 30 app. In such cases, the results will not vary much with different models and also with a finer grid UNLESS the code changes to near-wall solution instead of using wall models.

Now you need a low y+ in cases where you need to resolve the boundary layer characteristics or you expect a profound impact of the near-wall effects on the mean-flow. IN cases where the wall models provide sufficient near-wall accuracy, you may not need to resolve teh grid beyound the condition you have described.

Regards
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Old   February 2, 2006, 19:58
Default Re: y+
  #5
justin
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Hi, I amd study Y+ as well. My case is that a cube with side 6m in the wind tunnel and wind speed 10m/s. Re is about 4*106, roughness lengh is 0.01m. If I define y+ 60,the first distance is 4.6*10-7m. What is the problem?
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