Aerodynamic Drag

Also found in: Dictionary, Wikipedia.

aerodynamic drag

[‚e·ro·dī′nam·ik ′drag]
(fluid mechanics)
A retarding force that acts upon a body moving through a gaseous fluid and that is parallel to the direction of motion of the body; it is a component of the total fluid force acting on the body. Also known as aerodynamic resistance.

Aerodynamic Drag


head drag, a force which a gas (for example, air) exerts on a body moving through it; this force is always directed opposite to the direction of velocity and is a component of the aerodynamic force. Knowledge of aerodynamic drag is necessary for aerodynamic calculations of aircraft, since, in particular, the speed of motion for given thrust characteristics of an engine installation depends on this knowledge.

Aerodynamic drag is the result of the irreversible transformation of a portion of the kinetic energy of a body into heat. Aerodynamic drag depends on the shape and dimensions of the body, on its angle of attack, on the magnitude of velocity, and also on the properties and conditions of the medium in which motion takes place. In actual mediums there is viscous friction in the boundary layer between the surface of the body and the medium, and there are losses in the formation of shock waves at transonic and supersonic velocities (wave drag) and in the formation of vortices. The predominant component of aerodynamic drag depends on the flight conditions and shape of the body. For example, for blunt bodies of rotation moving at a high supersonic velocity, aerodynamic drag is determined mainly by wave drag. For streamlined bodies moving at a low velocity, aerodynamic drag is determined by friction drag and by losses in the formation of vortices.

In aerodynamics, aerodynamic drag is described by a nondimensional aerodynamic drag coefficient CD, through which the aerodynamic drag D is defined as

where ρ∞ is the density of the undisturbed medium, v∞ is the velocity of motion of the body relative to this medium, and 5 is the specific area of the body. The coefficient CD for a body of a given shape at a particular orientation relative to the flow depends on the non-dimensional similarity criteria, which include Mach numbers and Reynolds numbers. The numerical value of CD is usually determined experimentally, by measuring the aerodynamic drag in wind tunnels and in other devices used in aerodynamic experiments. Aerodynamic drag may be determined theoretically only for a limited class of the simplest bodies.


References in periodicals archive ?
Among the topics are safe road trains for the environment that reduce fuel consumption through a lower aerodynamic drag coefficient, low-cost autonomous vehicles for urban environments, system design and objective testing results for vehicle safety communications, a semi-autonomous system for testing with somnolent drivers, integrating controller design for path following in autonomous vehicles, and autonomous vehicle control in an urban environment by detecting map-based driving lanes.
Modern cars use virtually no extra fuel when they're re-started without pressing the accelerator so you won't waste it; | Drive smoothly - anticipate the road ahead to avoid unnecessary braking and acceleration; | Slow down - driving at 85mph uses 25% more fuel than 70mph; | Close your windows if you're going more than 60 mph - the aerodynamic drag will add to fuel usage; | Check tyre pressure at least once a month - under inflated tyres increase fuel consumption; | Get rid of excess weight - your car has to work harder to accelerate if it is heavier.
The force created by the aerodynamic drag of a vehicle goes up exponentially with the speed of the vehicle.
TransFoil Aerodynamic Skirts are attached to the sides of over-the-road (OTR) trailers to reduce aerodynamic drag and to improve fuel economy.
The car, which resembles the Batmobile, has half the weight, half the horsepower and half the aerodynamic drag of a typical prototype.
Cervelo's engineers carefully simulated each component on the S5, looking for ways to minimize aerodynamic drag.
The project brief was as follows: BAE Systems Munitions requires a fuzed projectile where the fuze function acts to improve the accuracy of the round on hitting the target using aerodynamic drag alone.
DRS reduces the aerodynamic drag by means of a movable flap in the rear wing, thus allowing cars greater straight-line speed than they would ordinarily achieve.
New injection, turbocharger, stop-start, brake energy recuperation, low rolling resistance tyres and a special grille shutter to reduce aerodynamic drag all combine to make the Focus sip fuel like a starling.
The two-plane wings have a slot in between that can be opened up by drivers to reduce aerodynamic drag and thus boost speed, The Sun reports.
And to that end it produces more aerodynamic down force without extra aerodynamic drag, and more power - 450bhp - without using more fuel.
Fuel consumption improvements over the outgoing Focus are said to be between 10 and 20% and engine stop-start, low-rolling-resistance tyres and aerodynamic drag reduction will all be used.