Calculating Drag Coefficient of a Car

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Discussion Overview

The discussion focuses on calculating the drag coefficient (CD) of a car, exploring methods to determine the drag force (FD) necessary for this calculation. Participants consider theoretical and practical approaches, including computational fluid dynamics (CFD) and wind tunnel testing.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant presents the formula for drag coefficient as CD=FD/0.5xρv^2A and expresses difficulty in finding FD without knowing CD.
  • Another participant suggests using computational fluid dynamics (CFD) to determine FD, noting that simplifications could allow for hand calculations, but emphasizes the complexity involved.
  • A different participant recommends using a wind tunnel as the typical method for measuring FD, indicating that analytical solutions may not be feasible for car shapes.
  • It is mentioned that the car will reach a specific steady state speed on the hill, which is necessary to calculate CD, with a proposed speed of "84.7 km/h."

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best method to find FD, with multiple competing views on the feasibility of CFD, wind tunnel testing, and the need for steady state speed information.

Contextual Notes

The discussion highlights the dependence on specific conditions, such as the car's speed on the hill, and the limitations of analytical methods for complex shapes like cars. The assumptions regarding the steady state speed and the applicability of CFD versus experimental methods remain unresolved.

philo2005
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Hi

I am currently trying to work out the drag coefficient of a car, I know the formulae to work out CD, this being CD=FD/0.5xρv^2A. I can not figure out how to find FD as the formulae for this requires CD. Is there another way to find FD? The information I have is as follows:

Car Mass: 1350 kg
Rolling Resistance: 400 N
Cross Sectional Area: 2.2 m^2
Density of Air: 1.23 kg m^-3
Hill Gradient: 3.18 degrees

I would greatly apprecitate any help offered as I am now completely stumped.

Thanks
 
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The way to work out Fd is through CFD. You could simplify it enough to do it by hand as well, but there really is no quick and easy way to do it.
 
The typical way to find Fd would be a wind tunnel. There isn't really any good way to do it analytically for a shape like a car.
 
From the looks of your info, the car in question will attain a specific steady state speed on that hill; you need to know that speed ("84.7 km/h") in order to figure out the Cd.
 

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