The Handiest CFD App – the Y+ Calculator

The Y+ Calculator app is a handy tool for calculating the grid spacing to achieve a target y+ value for viscous computational fluid dynamics (CFD) computations. Simply specify the flow conditions, the desired y+ value, and compute your grid spacing.

If you are an engineer running viscous CFD computations, setting the distance of the first grid point off the wall is essential for accurately resolving the boundary layer. Y+ is a non-dimensional measure of wall spacing that has been normalized by wall shear stress. For turbulent boundary layers, y+ should be 1.

The Y+ Calculator computes the height of the first mesh cell given a target y+ value and the flow conditions. The app works in either SI or Imperial units and quickly resets to sea-level conditions. Its computations are based on flat-plate boundary layer theory from Frank M. Whiteโ€™s Fluid Mechanics 5th edition, page 467.

The Y+ Calculator app is available for both iOS (left) and Android (right).

The Y+ Calculator is available for both iOS and Android so download your preferred version today. For more information see the Y+ Calculator page on our website.

Update: It’s worth noting that the app is free.

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2 Responses to The Handiest CFD App – the Y+ Calculator

  1. Alex says:

    1: Seems to be the only piece of software which does this locally — very good, and thank you
    2: Would have been nice if it also computed boundary layer thickness (for a flat plate), which could then also be used to work out how many inflation layers are needed, for a given first wall distance and expansion factor
    3: The interface is a little awkward because most of the screen is filled by the “keys”, and I can’t see all of my inputs at the same time. Old pocket calculators cannot show more than one number at a time, but modern smartphones don’t have that limitation ๐Ÿ™‚

    4: Would have been even nicer if it also included a standard atmosphere model to generate the inputs. I’m currently using a separate app to compute velocity, density and viscosity from altitude and Mach number, then transferring them, number by number, to the Y+ calculator.

    • John Chawner says:

      Thanks for the feedback, Alex. I’ll pass these ideas along to our programmers. I can’t guarantee when we’ll have another update because free stuff always goes to the bottom of the priority list.

      Also, if you have ideas for other CFD calculators besides Y+ that would be handy, please suggest them.

      Thanks again.

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