SDK Question Reynolds number.. how does Orbiter calculate it ?

[Mindblast]

In the AirfoilCoeffFunc callback that is passed to CreateAirfoil3 function the orbiter core passes the Reynolds number as one of the parameters. I'm wondering how this is calculated by orbiter ?

I'm trying to calculate a semi-realistic heat transfer coefficient for simulation of convection and found some equations on Wikipedia to calculate that from the Nusselt number which can be calculated from Reynolds number and Prandl number. What is needed there though is the characteristic length, which from what i read is also used to calculate the Reynolds number.

 

[Urwumpe]

characteristic length is one of the parameters you give to the CreateAirfoil function.

 

[Mindblast]

Oh right i found the formula in the API guide. I didn't think the chord length would be used as in the formula for Re-number for flow through a tube they used the diameter of the tube. But now i learned that the characteristic length is just used for getting the Re-number right in wind tunnel tests with scaled down models.

So apparearently i could just calculate Re number as

Re = rho * v / viscosity

assuming a characteristic length of 1.

I also found a formula on wikipedia for calculating the viscosity: http://en.wikipedia.org/wiki/Viscosity
about 1/3 into the article.. Sutherlands formula.