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June 13, 2016, 23:36 |
How much Y+ is enough in K-e model?
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#1 |
Senior Member
Aja
Join Date: Nov 2013
Posts: 496
Rep Power: 14 |
Hi,
I am running an axial turbine with RNG K-e turbulence model. Wall Function is scalable and Y+ contours are as follows: (please see range of Y+-I enable clip to range) 1. Is there any problem in these contours? 2. How much Y+ is enough in K-e model? What range is Y+ in K-e model? 3. If there is a problem in terms of Y+, What is your suggestion for solving this problem? Y+ On the blade: Y+ On the Hub more explanation about hub position: Thanks. Last edited by aja1345; June 17, 2016 at 14:59. |
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June 14, 2016, 00:09 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
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You need to check the sensitivity to y+ for your case. Run a simulation with a coarser or finer y+ and see if it makes a difference to parameters you care about.
You can't tell if the y+ is OK from a contour plot. |
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June 14, 2016, 00:19 |
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#3 | |
Senior Member
Aja
Join Date: Nov 2013
Posts: 496
Rep Power: 14 |
Thanks,
Quote:
I think that Y+ value have to be match with turbulence model. For example, Y+ should be equal to about 1 in K-W SST. Am I right? What is your idea? I am grateful that guide me more in detail. |
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June 14, 2016, 00:26 |
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#4 |
Senior Member
Aja
Join Date: Nov 2013
Posts: 496
Rep Power: 14 |
Is there difference between "grid sensitivity" and "grid independence"?
Could you please explain me the difference between the two terminologies, 'grid Independence' and 'grid Sensitivity ' |
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June 14, 2016, 03:03 |
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#5 | |||
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
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Quote:
Quote:
1) If the result is not sensitive to wall resolution 2) If the wall function approach works well then you want y+>11 You ONLY want y+=1 when you know you are sensitive to near wall resolution AND you know you need to integrate to the wall as the wall function approach will not work. Quote:
Grid independence means that when you change your grid your results do not change. This is what you want and is a necessary requirement for validation of a simulation. |
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June 14, 2016, 04:03 |
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#6 | |
Senior Member
Aja
Join Date: Nov 2013
Posts: 496
Rep Power: 14 |
Thanks for your clear reply.
Quote:
How do i find this maximum value? |
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June 14, 2016, 06:12 |
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#7 | |
Super Moderator
Glenn Horrocks
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Location: Sydney, Australia
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Quote:
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June 15, 2016, 10:39 |
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#8 |
Senior Member
Aja
Join Date: Nov 2013
Posts: 496
Rep Power: 14 |
Thanks.
Y+=11.225 is the transition to the log-law region. Now I have one question: We know that buffer layer is between 5 to 30. So it seems somehow wrong to place first layer in buffer layer! Can you explain in this case? |
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June 15, 2016, 19:58 |
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#9 | |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
Rep Power: 143 |
Quote:
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