#202 false reynoldsnumber over the span when the altitude is changed

[Marko J.]

Hello i have found an another bug in the version 6.57

Here is the description
create a wing with a generic airfoil.
define a LLT analysis with a air density at sealevel and 11000m altitude.

in xflr 6.57 the reynoldsnumber over the span is wrong implemented.
The reynoldsnumber is decreasing when the velocity is increased.

In the Attechment you will find the

• xfl-file
• png_1 for the drag velocity plot
• png_2 for the reynolds over span plot @ sealevel
• png_3 for the reynolds over span plot @ 11000m altitude

[Jochen Guenzel]

Hi Marko,
for me everything looks fine. The spanwise Re distribution is just a function of chord length. And for your test wing, the chord length is linearly decreasing - so does Re ...

An estimation of the absolute values:

The density in 10000m is about 1/3 to sea level. The speed of a plane flying at this altitude with the same CL is sqrt(3) => 1.7 higher - which fits to Xflr5.

At the same time Re is sqrt(3)/3 corrected with the dynamic viscosity => 0,7 lower. This is also ok with Xflr5.

regards
Jochen

[André]

Agree with Jochen.
Re =Ch V /nu
Speed increases but the dynamic viscosity is increased by a greater factor.

[Marko J.]

i'm sorry, you can close this ticket.

I have seen that the temperature is specified seperatly, so the viscosity is also changing due to temperature.

your feature was correctly implemented.