Calculating the Reynolds Number (Re) for a non-spherical object?

In summary, the Reynold's number can be calculated using the formula N_R = \frac{vL}{\nu} for non-spherical particles, with the length of the body parallel to the flow used as the characteristic dimension. This allows for the determination of drag coefficients and drag force for various shapes. However, for complex shapes, it is recommended to test for the proper drag coefficient.
  • #1
vette982
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I have the density (ρ) of the particles and the fluid, as well as the complete dimensions of the non-spherical particles. I know the Force of drag (F) and the Coefficient of drag (C). But how do you get the Reynolds number from this? I can't use Stokes' equations because they only apply to spheres.
 
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  • #2
What? Do you know what the Reynolds number is? What are doing that you need to know the Re?
 
  • #3
This thread has also been posted in physics section, there I asked for a better explanation of your question. Please don't post threads in multiple sections.
 
  • #4
vette982 said:
I have the density (ρ) of the particles and the fluid, as well as the complete dimensions of the non-spherical particles. I know the Force of drag (F) and the Coefficient of drag (C). But how do you get the Reynolds number from this? I can't use Stokes' equations because they only apply to spheres.

I presume you are referring to the Reynold's number as associated with the determination of drag coefficients - yes?

For non-spheres and cylinders it is common for some shapes to use the length of the body parallel to the flow as the characteristic dimension. So the normal relation one would use in fluid mechanics for pipe flow becomes:

[tex]N_R = \frac{vL}{\nu} [/tex]

Note that the only change is that the length of the body parallel to the flow(L) is used instead of the pipe diameter (D).

For complex shapes it is always recommended to test them for the proper drag coefficient.

Once you calculate the Reynold's number you can pick off the drag coefficient from a chart for that particular shape and then determine your drag force.

Hope this helps.

CS
 

1. What is the formula for calculating the Reynolds Number (Re)?

The formula for calculating the Reynolds Number (Re) for a non-spherical object is: Re = (ρVD)/μ, where ρ is the density of the fluid, V is the velocity of the fluid, D is the characteristic length of the object, and μ is the dynamic viscosity of the fluid.

2. What is the significance of the Reynolds Number (Re)?

The Reynolds Number (Re) is a dimensionless quantity that represents the ratio of inertial forces to viscous forces in a fluid flow. It is used to determine the type of flow (laminar or turbulent) and the resistance to flow of a fluid around an object.

3. How do you determine the characteristic length (D) for a non-spherical object?

The characteristic length (D) is the length of the object that is most representative of its size and shape. For a non-spherical object, it can be determined by taking the average of its longest and shortest dimensions, or by using the equivalent diameter of the object.

4. What are the units of measurement for the Reynolds Number (Re)?

The Reynolds Number (Re) is a dimensionless quantity and therefore has no units of measurement.

5. Is the Reynolds Number (Re) calculated differently for different types of fluids?

Yes, the Reynolds Number (Re) is calculated differently for different types of fluids because the density and dynamic viscosity of the fluid will vary. Therefore, the values for ρ and μ will change, resulting in a different value for Re.

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