CarSim+空气动力学+参考手册
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Mechanical Simulation VehicleSim Products
755 Phoenix Drive, Ann Arbor MI, 48108, USA
Phone: 734 668-2930 • Fax: 734 668-2877 • Email: info@carsim.com carsim.com
1 / 7 January 2018
Aerodynamics
Aerodynamic effects are represented in the vehicle model by a force acting on a point in the
sprung mass and moment vector the sprung mass. Each vector is built from three components (X,
Y, and Z) that are parallel with the axes of the sprung mass coordinate system. The three force
components are defined in terms of two dimensionless coefficients C
1
and C
2
, aerodynamic
cross-section area A, and dynamic air pressure Q:
F = C
1
•C
2
•A•Q (1)
where Q is:
Q =
r
V
2
2
(2)
r is air density, and V is air speed relative to the vehicle. Air density is normally 1.206 kg/m
3
.
The coefficients C
1
and C
2
differ for the three force directions. One is a function of aerodynamic
slip angle (b) and the other is a function of both vehicle ride height (Z) and pitch (q). (The
coefficients are specified as tabular functions of the dependent variables b, Z, and q).
The point of application of the aerodynamic forces is the aerodynamic reference point.
Aerodynamic effects are sometimes described in terms of a center of pressure, the point at which
at which no moments are required to produce all aerodynamic effects. By convention in
automotive engineering, however, aero effects are instead resolved to a set of forces at reference
location (reference point) and moments applied to the body.
The general form of a moment equation is similar:
M = C
1
•C
2
•A•L•Q (3)
where L is a reference length used to scale the moment equations. As with the force equations,
the coefficients C
1
and C
2
differ for the three moment directions. One is a function of
aerodynamic slip angle (b) and the other is a function of both vehicle ride height (Z) and pitch
(q).
In BikeSim, CarSim and TruckSim the six forces and moments can be described by 6
configurable functions that define the sensitivities of the coefficients in equations 1 and 3 to
aerodynamic slip angle. Each of these functions is represented with a separate library screen, as
summarized in Table 1.
Table 1 also includes two libraries used to define wind conditions: the amplitude (speed) and
direction (heading), where the heading is the yaw angle of the wind vector.
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