aerodynamic coefficients

Aerodynamic Coefficients


dimensionless quantities which characterize the aerodynamic force and moment acting on an object moving through a fluid or gaseous medium. The aerodynamic coefficients of a force CR are defined as the ratio of the aerodynamic force R to the velocity head (ρ v2)/2 and the characteristic area 5, and the aerodynamic coefficient of the moment CM, as the ratio of the aerodynamic moment M to (ρ v2)/2, S, and the characteristic length l —that is,

CR = R/½ρ v2S CM = M/½ ρ v2Sl

where ρ is the density of the medium through which the object is moving and ν is the velocity of the object relative to this medium. The characteristic dimensions are chosen rather arbitrarily. For an airplane, for example, S is the surface area of the supporting wings (in a plane) and / is the length of the wing chord; for a rocket, S is the surface area of the maximum cross section and / is the length of the rocket. If the aerodynamic force and moment are resolved into components along the coordinate axes, the following are obtained: the aerodynamic drag coefficient (C0), the lift and cross forces coefficients (Cu and Cz respectively), and also the aerodynamic coefficients of the rolling, yawing, and pitching moments.

The expression of aerodynamic forces and moments in the form of aerodynamic coefficients is very important in aerodynamic studies and calculations, simplifying them considerably. Thus, for example, the aerodynamic force acting on an airplane can attain values in the hundreds and thousands of kilonewtons (kN; tens and hundreds of ton-forces); the same force acting on the model of this plane which is being tested in a wind tunnel will be tens of newtons, but the aerodynamic coefficients for the airplane and the model will be equal.

Figure 1. Dependence of the aerodynamic drag coefficient of a cone on the Mach number

Figure 2. Dependence of the aerodynamic drag coefficient of a sphere on the Reynolds (R) number

For large devices flying at low altitude with subsonic velocity for which the Mach number is less than 0.2, the aerodynamic coefficient depends mainly on the shape of the aircraft and the angle of attack (the angle between the characteristic plane and the direction of velocity of the airplane). Generally, the aerodynamic coefficients depend on the viscosity and compressibility of the gas, which is characterized by dimensionless similarity criteria—the Mach number and the Reynolds number (see Figures 1 and 2).


aerodynamic coefficients

aerodynamic coefficientsclick for a larger image
Nondimensional coefficients for aerodynamic forces and moments. The most common are the coefficients of lift and drag (i.e., CL and CD).
References in periodicals archive ?
Uncertainty Analysis of Aerodynamic Coefficients in an Automotive Wind Tunnel, SAE: 01-0870.
For all measurement points a one page overview of the results, containing all wind tunnel settings, measurement description, the measured forces and the calculated aerodynamic coefficients is created as a pdf-file.
Therefore, further studies at full-scale Reynolds number should be performed to obtain an accurate prediction of full scale aerodynamic coefficients.
Actually, the equations derived using the inertial velocities incorporate the impact of the wind velocity when computing the aerodynamic coefficients.
Therefore, the aerodynamic coefficients are often assumed to be not dependent on the Mach number.
Extending flaps changes both the cord line and aerodynamic coefficients.
To provide accurate CFD unsteady flow data and aerodynamic coefficients.
existence of the VIP block reduces extreme aerodynamic coefficients on the nearest local roof zone by values from 0.
The following values for the aerodynamic coefficients of lift and moment in respect to the axis of tilt drawn in Figure 1 were found, as reproduced in diagrams 3 and 4.
During early stages of development, it was found that an important consideration was the balance of the bullet's physical configuration and aerodynamic coefficients, meaning the length of the ogive relative to the length of the cylinderical bearing surface.
The MathWorks today introduced Aerospace Toolbox, which provides reference standards, environmental models, support for importing aerodynamic coefficients, and three-dimensional visualization capabilities in MATLAB[?
The cooling module fans were assumed stationary for all simulations (in the experimental testing campaign, no appreciable difference in aerodynamic coefficients or local Cp values were seen if the fans were held stationary).