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  • About Y+ Ranges in Mini Project

    Posted by Ho Yin on July 17, 2023 at 1:32 pm

    Dear Sir,

    Lesson 25 covered two ways of capturing the boundary layers, one is the log-based wall function (having Y+ value from 30 to 300) , while the another is about the viscous sub-layers (Y+ value around 1). As taught the k epsilon and omega turbulence models are using the viscous sub-layers approach, does it mean the Y+ value of the boundary around the domain should always be monitored to maintain around 1? In such case, I would like to ask why the written example suggesting 50 as the targeted Y+ value?

    Based on the hand calculation, the desired first layer height of the Ahmed body is 3.26e-5m, which seems to be very fine and requires huge computational power.

    Also, may I ask some practical applications of log-based wall function for capturing the boundary layers, and could we find this method in Fluent?

    Thank you for answering!

    All the best,
    Jason

    Sandeep replied 8 months, 3 weeks ago 2 Members · 2 Replies
  • 2 Replies
  • Ho Yin

    Member
    July 24, 2023 at 8:01 am

    It is hoped for some clarifications to address my doubts or misunderstanding, thanks!

  • Sandeep

    Administrator
    July 25, 2023 at 10:23 am

    Hi jason,

    Good Question.

    It depends on us computational resources we have and the accuracy we are interested in.

    If we can keep Y+<1 we can capture the laminar sublayer and is more accurate. If we keep only up to 50 or 100 as Y+ we skip the actual capturing but instead, the inbuild wall function will be used in that region. This will result in less accuracy, but the results will be still OK.

    In fluent all these models are having inbuilt wall functions, you can check it in the GUI itself.

    Regards

    Sandeep

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