A. L. Chen
PhD dissertation, 1997.
The transient aerodynamic forces on automotive vehicles
traveling in close proximity to each other are investigated
in a wind tunnel. Scale vehicle models are
longitudinally aligned in a ``platoon" configuration with
various separation
distances between the models.
One model is actuated such that it is capable
of lateral motion at several accelerations with respect to the platoon.
The location of the
mobile model in the platoon is varied to simulate various lane
changing maneuvers of full scale vehicles.
The drag force, side force, and yawing moment are measured
with strain gage
balances to quantify the transient interactions of the vehicle
flow fields. Several important general trends can be observed.
The drag coefficients for the vehicles in a platoon
are lower than that of a single vehicle, and the coefficients decrease
with smaller vehicle spacings. In addition, the drag coefficients on the
remaining
vehicles increase as a
vehicle leaves the platoon. The side force coefficients also increase as a
vehicle
leaves the platoon. The increase in the side force is on the same order
as the increase in the drag.
The side force also increases with decreasing
vehicle separation.
Although the yawing moment is small, and thus, difficult to quantify,
the moment also reflects influences of the transient flow field.
A significant conclusion of the results
is that the transient forces
differ depending upon whether a vehicle leaves or
joins a platoon. This hysteresis in the flow dynamics is not
observable in steady-state measurements.
View pictures of the experiment: