The reynolds number equation, .

In summary: In that example, the Reynolds Number would beRe = \rho *D *VRe = 6.8 x 10^{5} \text{N}You would find the Reynolds Number on a Cd Chart.
  • #1
picklefeet
16
0
I understand most of the equation.

[tex] Re=\rho *D *V
over a symbol I don't recognize

I don't know what the symbol is the denominator, and I can't find its name so I don't know what it means. I just need one definition, thanks.
 
Last edited:
Physics news on Phys.org
  • #2
http://en.wikipedia.org/wiki/Reynolds_number"
 
Last edited by a moderator:
  • #3
Its the viscosity, mu.
 
  • #4
I was given the above equation in order to find drag coefficient through estimation and Reynolds Number. Where would I find a Reynolds Number - Cd Chart?
 
  • #5
I'm having a problem with another related problem. If I wanted to find terminal velocity, the Cd=1.17, the Ac=.4522 m^2 and the weight equalled 5.67 grams or.0556037055 Newtons and the air density is 1.184 with no turbulance, what do you get? I think the problem may be my arithmetic.
In the terminal velocity equation, I get .33347775 over .7914693. I know this isn't right. What am I doing wrong?
 
  • #6
Interesting... Since you apparently know when you have the wrong answer, how about you just go through and eliminate every answer that you know is not right until you only have only one answer left over. That answer, by process of elimination, must be the right one.

This method of solution may be applied to all of your homework problems without fail.
 
  • #7
picklefeet said:
I'm having a problem with another related problem. If I wanted to find terminal velocity, the Cd=1.17, the Ac=.4522 m^2 and the weight equalled 5.67 grams or.0556037055 Newtons and the air density is 1.184 with no turbulance, what do you get? I think the problem may be my arithmetic.
In the terminal velocity equation, I get .33347775 over .7914693. I know this isn't right. What am I doing wrong?
First off, if you are still talking about a quarter, the area you are using is way off. The measured diameter of a quarter is about 24 mm. Therefore the area is

[tex]A =\frac{1}{2}*\pi*(24 x 10^{-3} m)^2[/tex]

[tex]A = 4.52 x 10^{-4}[/tex] [tex]m^2[/tex] or [tex]A = .000452[/tex] [tex]m^2[/tex]

The variable that you are asking about, [tex]\mu[/tex] is the dynamic viscosity of the medium the object is moving in, i.e. air. In that example, the seal level value for [tex]\mu = 1.79 x 10^{-5}[/tex] [tex]\frac{N*s}{m^2}[/tex]

Reynolds Number is a unitless number, i.e. all units should cancel out when it is calculated.
 
Last edited:

1. What is the Reynolds Number equation?

The Reynolds Number equation is a dimensionless quantity that is used in fluid dynamics to predict the type of flow (laminar or turbulent) that will occur in a given fluid. It is calculated by dividing the product of the fluid's velocity, density, and characteristic length by its dynamic viscosity.

2. How is the Reynolds Number equation used?

The Reynolds Number equation is used to determine the transition from laminar to turbulent flow in a fluid. It is also used to study the flow of fluids in pipes, channels, and over surfaces. It can help engineers design more efficient and effective systems, as well as predict potential flow problems.

3. What is the significance of the Reynolds Number?

The Reynolds Number is significant because it helps determine the type of flow that will occur in a fluid. Laminar flow is smooth and predictable, while turbulent flow is chaotic and less predictable. The value of the Reynolds Number can also indicate the presence of flow instabilities or the potential for flow separation.

4. What are the units for the variables in the Reynolds Number equation?

The units for the variables in the Reynolds Number equation are as follows: velocity (m/s), density (kg/m^3), characteristic length (m), and dynamic viscosity (Pa*s). The Reynolds Number itself is a dimensionless quantity, meaning it has no units.

5. How does the Reynolds Number affect drag?

The Reynolds Number can have a significant impact on the amount of drag experienced by an object in a fluid. For low Reynolds Numbers, the flow around an object is primarily laminar and has lower drag. As the Reynolds Number increases and the flow becomes more turbulent, the drag also increases. This is why cars and airplanes have streamlined designs to reduce drag and improve efficiency.

Similar threads

I How is the Reynolds number derived (is my derivation wrong)?
    • Other Physics Topics
Replies
6
Views
2K
Pressure drag and the Reynolds number
    • Aerospace Engineering
Replies
5
Views
2K
Nozzle loss coefficient that increases with Reynolds number?
    • Mechanical Engineering
Replies
3
Views
1K
Trouble calculating the Reynolds number
    • Other Physics Topics
Replies
14
Views
2K
I Laminar-turbulent transition and Reynolds number
    • Classical Physics
Replies
5
Views
956
Fully developed flow, Reynolds number
    • Other Physics Topics
Replies
12
Views
3K
I Reynolds Number in Organism-Fluid Interactions
    • Classical Physics
Replies
4
Views
2K
Pipe Friction, Reynolds number & Bernoilli's Equation
    • Introductory Physics Homework Help
Replies
7
Views
1K
At what critical Reynolds number does vortex shedding begin?
    • Mechanical Engineering
Replies
9
Views
2K
Physical Interpretation of Reynolds Number
    • Other Physics Topics
Replies
2
Views
8K

Hot Threads

Recent Insights

Back
Top