Calculating Reynold's Number for a Passenger Jet Cruise

In summary, the cruise Re number for a passenger jet traveling at 525 mph with a wing chord of 3 m and in an altitude of 39,000 ft, is approximately 15667833.16. This was calculated using the equation Re=(pvL)/u, where p is density, v is velocity, L is length, and u is dynamic viscosity. The units used were consistent, with density in kg/m^3, velocity in m/s, and dynamic viscosity in N-s/m^2.
  • #1
Spartanlol
19
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A passenger jet cruises at 525 mph and an altitude of 39,000 ft. The wing chord is 3 m. If the local density is 6.14 x 10-4sl/ft3 and the dynamic viscosity is 2.97 x 10-7lbf-s/ft2, what is the cruise Re number based on the chord? Make sure your units are consistent in your calculations!



2. Equation for Re, which I believe is Re=(pvL)/u where p=density, v=velocity, L=length, u=dynamic viscosity. We haven't been taught the equation, supposed to find it online, and I believe this is it.



3. My issue is I am confused as to what units I should keep everything in and also I have no idea what lb-s/ft2 is.
 
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  • #2
Why don't you look up (or write down) the units of viscosity that you are familiar with, and maybe you can work backwards from that (swapping one at a time a metric-type unit into its imperial version) to allow you to figure out these imperial ones.

lbf is probably pounds or pounds force, but I'm guessing.
 
  • #3
UPDATE

Just tried to solve it myself and I think it worked. I turned 6.14x10^-4 slug/ft^3 to .3164 kg/m^3, 525mph to 234.696 m/s, and 2.97x10^-7 lb-s/ft^2 to 1.422x10^-5 N-s/m^2

I think those were the correct unit required to keep this dimensionally homogeneous since Re number is unitless. I am pretty sure my conversions are correct, if anyone notices one is off please tell me. After typing these into the equation (I didn't round on my calculator for these conversions like I showed here) I ended up with Re=15667833.16

I am not sure if that is it or if it's even a reasonable number (never used Reynold's equation before) so please tell me if this looks strange.
 

1. What is Reynold's Number Calculation?

Reynold's Number Calculation is a dimensionless number used to determine the type of flow in a fluid (laminar or turbulent) based on its velocity, density, viscosity, and length scale.

2. How is Reynold's Number Calculation calculated?

Reynold's Number Calculation is calculated by multiplying the fluid's velocity by its characteristic length and dividing the result by its dynamic viscosity.

3. What is considered a high Reynold's Number?

A high Reynold's Number indicates a turbulent flow, typically greater than 4000.

4. How is Reynold's Number Calculation used in practical applications?

Reynold's Number Calculation is used in various engineering applications, such as determining the type of flow in piping systems, designing aircrafts and ships, and predicting drag forces on objects in a fluid.

5. What are the limitations of Reynold's Number Calculation?

Reynold's Number Calculation is limited to Newtonian fluids and does not account for complex fluid behaviors such as compressibility, non-Newtonian behavior, and flow instabilities.

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