I’m trying to simulate an aerofoil based on experimental data with flow in the following conditions:


Reynolds number (Re) = 3*10^6

I wanted to keep my chord length at 1unit but then what would I use as my free stream flow velocity in my pressure far field boundary condition? Does the Reynolds number even matter here?

Would it be correct to say that the Re doesn’t matter here as I know M=0.8?


1 Answer 1


This depends on what kind of flow solver you are using and how it is set up.

Mach and Reynolds numbers appear when we write the flow equations in a non-dimensionalized form. So often, these codes have Mach and Reynolds numbers as direct inputs and the pressure, density, and temperature they work with are in somewhat odd scaled forms.

  • $\begingroup$ I’m using a density based solver. I thought that as the Re and Mach cannot be both inputted, but the Mach can be inputted directly into my pressure far field boundary condition, the Re number doesn’t matter? $\endgroup$
    – SirTimothy
    Commented Oct 25, 2023 at 16:20
  • $\begingroup$ Are you running in an invsicid mode? Do you have to turn on viscous terms separately? If so, I would expect Re to become an option when you turn on the viscous terms. It also will probably be a 'Reynolds Number per mesh length'. I.e. If the chord is 1.0, then you could think of it as the Reynolds number at the chord length (at scale). $\endgroup$ Commented Oct 25, 2023 at 19:44
  • $\begingroup$ Hi, I’m running with inviscid assumptions. I’ll look more into what you’re saying, thank you $\endgroup$
    – SirTimothy
    Commented Oct 26, 2023 at 19:37
  • $\begingroup$ @SirTimothy Great. With inviscid assumptions, Re has no meaning. Even if you eventually want to run a viscous solution, starting inviscid is often a good idea. You will be able to get some experience with a case that is easier to set up and that will run faster. $\endgroup$ Commented Oct 26, 2023 at 21:07
  • $\begingroup$ Hi Rob, thanks you for that! Why/when would you run a viscous simulation please? $\endgroup$
    – SirTimothy
    Commented Oct 27, 2023 at 12:26

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