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Suitable Y-plus values for SST with "Automatic near wall treatment" |
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#1 |
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Johan Björk
Join Date: Nov 2017
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Hello!
I am currently doing my master thesis project which consists of performing CFD analysis of a centrifugal compressor in a turbocharger. One of the first parts of this project is to do a mesh study to determine how refined my mesh needs to be in order to get the requested simulation data in the least computational heavy simulation. when it comes to the CFX setup, the company that I perform this project at has from previous work found out that the best suitable turbulence option is the SST Menter k − ![]() I have read in the Ansys help that when using automatic near wall treatment, the solver based on both wall functions and Low-Reynold-Number methods overcomes the grid resolution requirements by gradually switching between wall function and LRN method. From what I have understood, the automatic near wall treatment will switch to wall function treatments when ![]() ![]() For that reason, I have tried to find answers to this online, where some say that the switch happens at ![]() I am planning to make the mesh refined enough to avoid switching between wall functions as far as possible by having a refined mesh that puts me in the lower region. I would be very thankful if someone can help me with this question. Thanks in advance! /Burken |
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#2 |
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Glenn Horrocks
Join Date: Mar 2009
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This is discussed in section 2.8.1.2 of the CFX theory manual, particularly equation 2.229 (CFX V19 help files). Eqn 2-229 is y+ = max(y*,11.06), so the y+ is limited to 11.06.
I do not know where you got y+=2 as the switch from.
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#3 | |
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Johan Björk
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Quote:
I have read in section 4.2.3 from version 18.2: "However, a strict low-Reynolds number implementation of the model would also require a near wall grid resolution of at least ![]() /Burken |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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The quotation says that for good resolution when integrating to the wall you need y+<2, but for most cases this is difficult to achieve everywhere so the approach used by CFX can handle larger y+ than that by switching to wall functions.
The switch occurs at y+=11.06.
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Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. |
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#5 | |
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Johan Björk
Join Date: Nov 2017
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Quote:
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Tags |
ansys, cfx, sst, wall functions, y plus |
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