Calculating Force of Drag Using the Reynolds Number

In summary, the conversation is about the relationship between Reynolds number, inertial forces, viscous forces, and drag. The Reynolds number is equal to the ratio between inertial forces and viscous forces. The force of drag, Fd, is dependent on the viscosity of the air and the relative magnitude of the viscous forces to the motion of the flow, expressed as the Reynolds number. However, it is not equal to inertial forces alone, as it also takes into account the contribution of viscous forces. There are two regimes of drag, turbulent and linear, which can be further understood by looking at the Navier-Stokes equation and researching more on the topic.
  • #1
luckis11
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  • #3


See

http://en.wikipedia.org/wiki/Drag_(physics )

There are two regimes, turbulent (high Reynold's number) and linear (Stokes) drag.

Bob S
 
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  • #4


I meant how Fd is related to:

(Reynolds Number)=(Inertial Forces)/(Viscous Forces)
 
  • #5


luckis11 said:
I meant how Fd is related to:

(Reynolds Number)=(Inertial Forces)/(Viscous Forces)

Did you not read the link I gave you?

...For the gas, the magnitude depends on the viscosity of the air and the relative magnitude of the viscous forces to the motion of the flow, expressed as the Reynolds number...

CS
 
  • #7


"...For the gas, the magnitude depends on the viscosity of the air and the relative magnitude of the viscous forces to the motion of the flow, expressed as the Reynolds number..."

So? We have:
Re=(inertial forces)/(viscous forces)

At wiki it says
" Note that this (Re) is equal to the ratio between...which is the drag (up to a numerical factor, half the drag coefficient)..."

So, Fd=(inertial forces)?
Should't it be Fd=(inertial forces)+(viscous forces)?

Both wrong? Any site making all this a bit clear?
 
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1. What is the Reynolds Number?

The Reynolds Number is a dimensionless quantity used in fluid mechanics to indicate the ratio of inertial forces to viscous forces in a fluid flow. It is named after British scientist Osborne Reynolds.

2. How is the Reynolds Number calculated?

The Reynolds Number is calculated by dividing the product of the fluid density, velocity, and characteristic length by the fluid viscosity. The characteristic length is typically the diameter of the object in the fluid flow.

3. What does the Reynolds Number indicate?

The Reynolds Number is used to determine the type of flow in a fluid. A low Reynolds Number (less than 2300) indicates laminar flow, while a high Reynolds Number (greater than 4000) indicates turbulent flow. A Reynolds Number between these two values indicates transitional flow.

4. How is the force of drag calculated using the Reynolds Number?

The force of drag can be calculated using the Reynolds Number by using the drag coefficient, cross-sectional area, and fluid density in the drag equation. The drag coefficient is a dimensionless quantity that is dependent on the shape and roughness of the object in the fluid flow.

5. What are some real-world applications of using the Reynolds Number to calculate force of drag?

The Reynolds Number is commonly used in the design of aircraft, ships, and cars to optimize their aerodynamic performance. It is also used in the design of pipelines, pumps, and other industrial equipment to minimize drag and improve efficiency. Additionally, the Reynolds Number is used in sports, such as swimming and cycling, to improve performance by reducing drag on the human body.

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