1975-02-01

Development of Devices to Reduce the Aerodynamic Resistance of Trucks 750702

A summary of AeroVironment Inc. research programs in Truck Drag Reduction is given. These programs involve analytical studies, wind tunnel testing, full-scale field tests, full-scale road test, and operational testing. A number of different test methods and instrumentation techniques have been perfected which operate simply and reliably, and give precision of higher than 2% under windless conditions.
A discussion of the basic elements of bluff body drag, as it relates to truck air resistance is given. The concept of a dragless forebody is introduced. It is shown that this dragless state can nearly be achieved with a lip-like device on the front face of the van. The shielding effect of one body ahead of another is described, and the deleterious effects of crossflow in the gap between the bodies is discussed. In particular, it is shown that some add-on devices are particularly susceptible to crosswind flows and lose effectiveness at a few degrees of yaw.
Two devices, one, the lip, for the front face of the van body, and the other, the perforated screen for tractor mounting, are described, with their principles of operation. These devices have been road tested and give very substantial savings in aerodynamic drag coefficients, exceeding 30% in both cases. The fuel savings associated with such devices depend upon payload, speed, etc., but can be as much as 60% of the aerodynamic drag saving.
The importance of full-scale testing under operational conditions is pointed out with particular reference to random wind effect. It is noted that the devices described appear to function well under crosswind conditions.

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