Calculating Force of Drag Using the Reynolds Number

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    Drag Force
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Discussion Overview

The discussion revolves around the calculation of the force of drag using the Reynolds number, exploring the relationship between inertial and viscous forces in fluid dynamics. Participants are examining theoretical aspects and seeking clarification on how drag is quantified in different flow regimes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the force of drag (Fd) could be equated to inertial forces, questioning if this is a valid assumption.
  • Others mention that drag is a mechanical force and reference external sources to support their claims.
  • One participant highlights the existence of two regimes of drag: turbulent (high Reynolds number) and linear (Stokes) drag, indicating different behaviors in fluid dynamics.
  • There is a suggestion that the relationship between Fd and the Reynolds number is not straightforward, with one participant questioning whether Fd should include both inertial and viscous forces.
  • References to external sources, such as the Navier-Stokes equation and Wikipedia, are made to provide context and further information on the topic.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between drag and the Reynolds number, with no consensus reached on whether Fd should be considered solely as inertial forces or if it should also account for viscous forces.

Contextual Notes

Participants acknowledge that the understanding of drag force may depend on the definitions used and the specific conditions of the flow, such as viscosity and flow regime, which remain unresolved in the discussion.

luckis11
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See

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

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

Bob S
 
Last edited by a moderator:


I meant how Fd is related to:

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


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
 


"...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?
 
Last edited:

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