Calculating Drag Coefficient of a Car

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SUMMARY

The drag coefficient (CD) of a car can be calculated using the formula CD = FD / (0.5 * ρ * v² * A). To determine the drag force (FD), computational fluid dynamics (CFD) or wind tunnel testing are the most effective methods, as analytical solutions are not practical for car shapes. Given the car's mass of 1350 kg, rolling resistance of 400 N, cross-sectional area of 2.2 m², air density of 1.23 kg/m³, and a hill gradient of 3.18 degrees, the steady-state speed required to calculate CD is approximately 84.7 km/h.

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  • Knowledge of computational fluid dynamics (CFD) tools
  • Basic physics concepts related to forces and motion
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Automotive engineers, aerodynamicists, and physics students interested in vehicle performance optimization and drag coefficient calculations.

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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