[K1650369]

Hi All,

I am a little confused as to the different values different sources are using for calculating the wall spacing for meshing and inflation layer.

In the online y+ Calculator of Pointwise (http://www.pointwise.com/yplus/), they use a Dynamic Viscosity of 1.8375 x 10-5 Kg/m/s and a Density of 1.225 Kg/m-3 (same value used in many sources).

However, for International Standard Atmosphere definition, a density of 1.225 Kg/m-3 corresponds with sea-level, which also corresponds with a Dynamic Viscosity of 1.789 x 10-5 Kg/m/s.

Why does pointwise (and other sources) use a different value to ISA definitions?

Many thanks for your help.

[LuckyTran]

As usual, standards are non-standard.

It differs of course what pressure & temperature you take. Of course, 1.225 kg/m^3 is not a very good density to use if you are at 300 K and 1atm (1.18 kg/m^3 is a better number). You should of course update these values for your problem; any decent y+ calculator will let you do this. There's no point taking the properties of any standard atmosphere when that's not the air you are dealing with. Since nobody states exactly what P,T, and equation of state they use to calculate these values, they are never wrong. Actually if you look closely at the table in Frank White's book, you'll realize it uses ideal gas law and is not an actual property table (i.e. not from a database) for air at the stated temperatures and pressures.