Reynolds number calculation for undergraduate

[ra180]

Calculate the Reynolds number at a location χ= 0.3m along the chord length of an aircraft wing at each of the following velocities;u= 20,40,60,80 and 100 knots. Assume International Standard Atmosphere (ISA) conditions for pressure and temperature. Take; R =287 J/KG;μ= 18 X10 -6 Kg/m s; 1 knot = 0.869 1mph= 1.61km/h

If someone could answer this in a step by step manor that would help me greatly. (I have been offered a retake for a mitigating circumstance at my University)

 

[Travis_King]

As this reads as a homework question, as per the rules, you have to provide your work and attempt at a solution along with any figures or tables accompanying the question. Even if it isn't, if you want to learn the material, try it first then you'll find help here.

 

[ra180]

Thanks Travis can i post photos of calculations i have tried?

 

[boneh3ad]

Of course you can do that, and we encourage you to do that.

 

[ra180]

Sorry guys I have been really busy here is my answer.

Assuming ISA P= 101325pa ,R= 287 J/kgk and T=288.15K

Convert knots into meters per second

(1) 20 knots= 10.29/ms, 40 knots =20.58m/s 60 knots= 30.87 m/s 100 knots =51.44 m/s

(2) Using the formula R= ρux/μ where (ρ= P/RT) (u= velocity in m/s-1) (x=0.3) and (μ= 18 x10-6)

(3) Final answer at 20 knots Reynolds number = 210088, 40 knots = 420175, 60 knots = 630263, 80 knots = 8402350, 100 knots = 1050233

 

[Travis_King]

Looks good to me, looking at the 20 knot answer. Note also that sometimes the Reynolds number over an airfoil will read as R=V*Xc / v where Xc is the location along the chord length and v is the kinematic viscosity, which is equal to μ/ρ.

Edit: though I think you have an extra 0 in the first one, that should be 210087.

What does this tell you about the boundary layer conditions at these locations?

 

[ra180]

Would you believe that is the next question should I start a new thread or continue posting here?