What is a Drag Coefficient?

In this video, we will be discussing Drag Coefficients. What are they? How can you calculate them? And most of all, how you can use them in your design process! Theory Drag coefficients are used to calculate the hydrodynamic (in water) or aerodynamic (in air) force on an object, given the density Rho (ρ), the speed (u) and the frontal area (A) of an object. So if you know the force on an object at a certain speed, for example after a wind tunnel test, you can calculate the drag coefficient yourself using this formula. (0:28) Once you know the drag coefficient for a certain geometry, you can calculate the force for different object sizes or different velocities That is very useful for example when you need to size engines, calculate required battery capacity, etc. But keep in mind that the drag coefficient can vary in function of the Reynolds number. So be careful with large extrapolations to other speeds, sizes or densities. Practical use A drag coefficient allows you to analyze the aerodynamic efficiency of an object, irrespective of its size or velocity. That makes it possible to compare a cyclist for example to a building. They are quite different, but still, they have a normalized aerodynamic coefficient. It is also quite useful within a design process: when you are looking at different concepts for example for your new project or new vehicle, you can rank them according to their drag coefficient. Or you could get inspired by aerodynamic shapes coming from a completely different sector (Mercedes once had a car design inspired by fish!). Typical Values A drop shape, which is quite efficient, can have a drag coefficient as low as 0,05, whereas a building typically has one above 1. Lower means more streamlined. So if you are working on a drone that needs to fly as far as possible on a single charge or a cyclist that wants a higher top speed, you will want to reduce the drag coefficient as much as possible. ----------------------------------------------------------------------------------------------------------- Wouter Remmerie Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week! Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it? Check out https://www.AirShaper.com and see how easy it can be!

Supported by

  • openfoam-logo
  • liso-logo
  • imec
  • start-it-kbc

Code contributions by

  • KU Leuven
  • Inholland
  • Linkoping University