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 cfdman_aero February 23, 2012 03:36

k-epsilon near wall conditions

hi every body
I have written my cfd code to solve incompresible turbulent flow past a cylinder by finite volume method. I have some troubles in source terms of k and epsilon near wall. I dont know if I should do mesh refinement or use wall functions. Please let me know how to implement them. Note that the equations are nondimensional so for example how can I specify Y-Plus.

thanks.

 xiandjf February 23, 2012 04:15

for k-epsilon model,Y-plus between 100 and 200 is all ok!

 cfdman_aero February 23, 2012 07:44

tank you but would you please tell me aboaut near wall treatment of k-epsilon!?

 eishinsnsayshin February 24, 2012 13:47

Someone might correct me but I thought for k-epsilon you needed y+ between 30 and 200. You can't be below 30 because this will be in the buffer layer (but you can be really close to 30). The right number of y+ depends on pressure gradient. For adverse pressure gradients you need a closer y+ (closer to 30) and for favorable pressure gradients you can get up towards that 200 number. That's why this range exists in the first place.

Now your question was about near wall treatments. I think this needs y+ less than 5 because you're actually resolving the laminar sublayer so you need those nodes there.

My question to someone else out there is: is this still correct for the finite volumes, not finite differences? Does it matter?

 cfdman_aero February 24, 2012 14:12

source term

yes I have also trouble in descritizing of nonlinear source terms of k and epsilon equations by finite volume.

 heidar February 26, 2012 15:59

sugestion

dears
Using K-e model near wall or using a wall treatment method depends on your accuracy requsition. nonetheless, i suggest you to use a wall treatment modelization near the walls to save time due to the little effects of using K-e model near wall in comparison with wall treatments.
you could use wolf-steinn as a one equation model, K-w model or wall functions to predict the fluid flow or heat transfer near the boundries which directly depends on your data request.

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