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Homework Help: Reynolds number calculation for undergraduate

  1. Jul 23, 2014 #1
    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)
  2. jcsd
  3. Jul 23, 2014 #2
    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.
  4. Jul 23, 2014 #3
    Thanks Travis can i post photos of calculations i have tried?
  5. Jul 23, 2014 #4


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    Of course you can do that, and we encourage you to do that.
  6. Jul 29, 2014 #5
    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
    Last edited: Jul 29, 2014
  7. Jul 29, 2014 #6
    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?
    Last edited: Jul 29, 2014
  8. Jul 29, 2014 #7
    Would you believe that is the next question should I start a new thread or continue posting here?
    Last edited: Jul 29, 2014
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