CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   Main CFD Forum (https://www.cfd-online.com/Forums/main/)
-   -   Reynolds number for Wing analysis (https://www.cfd-online.com/Forums/main/112219-reynolds-number-wing-analysis.html)

 solar.spectrum January 24, 2013 00:52

Reynolds number for Wing analysis

hey guys, I would like to know about reynold's number for a wing

I have designed a NACA 4412 wing which has wingroot = a , wingtip = b and winglet tip = c (a,b,c are any integers or decimals)

please tell me the formula of calculating D for the eqn of reynolds number = VD/

additional info : Wing taper ratio = 0.3 , sweep and sweepback angle = 37 degree

altitude = 6000m , density = 0.65970 kg/m3, Pressure = 47182.5 Pa ,
Temp= 249.2K , velocity of freestream= 100m/s, viscosity= 0.00001594 N sec/m^2

 truffaldino January 24, 2013 07:13

The definition of Re in this case depends on your purpoces. Do you want to comute Lift, Drag, CM?

 solar.spectrum January 24, 2013 13:25

Quote:
 Originally Posted by truffaldino (Post 403745) The definition of Re in this case depends on your purpoces. Do you want to comute Lift, Drag, CM?
yes, I want to calculate lift and drag for different reynolds number as well as Angle of attack

 FMDenaro January 24, 2013 13:32

your characteristic length "D" is the one that is meaningful for your problem ... any choice of a lenght is coherent with the definition of a Reynolds number, but if you want that the Re number represents the relative magnitude between convective and diffusive fluxes of the momentum quantity for your problem, then you have to choice properly the lenght..

 truffaldino January 24, 2013 18:28

Quote:
 Originally Posted by solar.spectrum (Post 403834) yes, I want to calculate lift and drag for different reynolds number as well as Angle of attack
What method or sotware are you going to use?

In general, single reynolds number fits only for calculation of 2D airfoil. In your case the analysys should be more sophisticated, unless you are going to have a rough estimation.

Tell us more details.

 A.D.E January 28, 2013 11:57

For a 2D wing (airfoil) you can use your chord length to calculate the value of Re!! If you have a tapered 3D wing then the Re will vary at the different locations. You can however calculate an average Re based on your average chord length. A more in-depth analysis can be obtained at:

Fundamentals of Aerodynamics SI by John D. Anderson

And/or

Aerodynamics for Engineers John J. Bertin, Russell M. Cummings

 Hybrid January 28, 2013 12:51

You have to compute the "Mean Aerodynamic Chord" and use that as a characteristics length "D" in Reynolds number formula. The formula for MAC is:

MAC = A-(2(A-B)(0.5A+B) / (3(A+B)))

here, A : Root chord of the wing
and B: Tip chord of the wing

This equation for the straight-tapered wing.