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What y+ value shall we choose for laminar flow? |
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October 4, 2012, 07:48 |
What y+ value shall we choose for laminar flow?
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#1 |
Senior Member
lnk
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Hi,
May I ask what y+ value shall we choose for laminar flow? Is that the same as for turbulent flow? Could I still use the calculator given by this forum? (http://www.cfd-online.com/Tools/yplus.php) Thank you very much. lnk Last edited by lnk; October 4, 2012 at 13:25. |
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January 26, 2013, 05:58 |
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#2 | |
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Meimei Wang
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January 27, 2013, 12:13 |
viscous-sub-layer
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#3 |
New Member
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The y+ value is important for the turbulent-model. It defines the height of the viscous-sub-layer where a laminar flow near the wall in turbulent flows occurs. I'm not a specialist but i would say it doesn't matter how big the height of your first cell is because there isn't a turbulence model.
regards |
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January 27, 2013, 15:51 |
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#4 |
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mohsen
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hi the y+ is only important for turbulent flow because it used in turbulent flow.
boundary layer is three region in turbulent flow they are sub layer , buffer layer & log layer. velocity is linear in sub layer and it's logarithmic for log layer. if y+ was below 5 then the first cell is in sub layer. velocity for first cell obtain linearly if y+ was larger than 30 the the first cell is in log layer . velocity for first cell obtain logarithmic. however boundary layer of laminar flow is one region and it's velocity is defined we do'nt need y+ for laminar flow |
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January 27, 2013, 17:24 |
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#5 | |||
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Lucky
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Quote:
Quote:
Quote:
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January 28, 2013, 08:47 |
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#6 |
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Filippo Maria Denaro
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Consider the example of the plane channel flow. Then,
y+ = u_tau *y/ni = (u_tau *H/ni) * (y/H) = Re_tau* y' being y' the non-dimensional position along the vertical direction. Assuming that y'=1 in the half-heigh of the channel, as in laminar flow one assumes Re_tau=O(1), you see that y+ will be very very small close to wall and will be O(1) in the half-height. |
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February 2, 2013, 08:24 |
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#7 | |
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Meimei Wang
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Quote:
Thanks for your answer. But in order to resolve laminar boundary layer well, we still need a lowest wall cell width criteria, right? For example, what wall cell width would you choose for laminar pipe flow?
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February 3, 2013, 05:29 |
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#8 |
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venki
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calculate first cell height based on boundary condition
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February 6, 2013, 12:11 |
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#9 |
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Meimei Wang
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Could you briefly give a short example of how? Thank you very much.
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February 15, 2013, 10:17 |
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#10 |
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Lefteris
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You can calculate the maximum displacement of the boundary layer from the Blasius solution and then you can figure out how many points you need in order to cover this (with a geometric distribution let's say) after you decide your initial ds. Usually, the initial ds should be small enough, let's say of order 10^-4.
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February 15, 2013, 16:27 |
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#11 | |
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Lucky
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I usually take 3 orders of magnitude less the boundary layer thickness and then take half that height if I want to be conservative. El. K. suggested 10^-4 which should also work. You just need to estimate the boundary layer thickness somehow (can always resort to Blasius solution). |
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March 3, 2013, 18:54 |
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#12 | |
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Meimei Wang
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March 4, 2013, 04:56 |
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#13 | |
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andy
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Quote:
Laminar flows have no turbulence models and hence have none of these constraints on y+ for the first cell. What is required for the first cell and every other cell in the grid is that the gradients in the flow are adequately resolved. This is a function of the discretisation scheme and how well the gradients need to be resolved at the cell location. For example, a fully developed flow in a pipe may require only 1 cell to be fully resolved with a higher order numerical scheme or tens of cells for a low order scheme. A resolution criteria based on y+ is going to be rather limited in applicability compared to a normal one based on gradients of the solution variables. |
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August 27, 2015, 13:09 |
y+ value
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#14 | |
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AZ
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August 4, 2016, 05:23 |
y+ value or first cell height for laminar flow
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#15 |
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Vijaya Kumar. G
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This may help
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February 15, 2017, 14:34 |
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#16 |
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Hamed Abdul Majeed
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November 23, 2021, 09:24 |
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#17 |
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Valarivan
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Location: Tamil Nadu, India
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DEVELOPED LAMINAR FLOW IN PIPE USING COMPUTATIONAL
FLUID DYNAMICS by M.sahu and et http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf http://www.fem.unicamp.br/~phoenics/...l%20fluent.pdf Last edited by Valarivan; November 23, 2021 at 21:28. |
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February 23, 2024, 23:32 |
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#18 |
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Nigeria
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