How do Scientists study Drag?
It is important to identify the sources of drag in order to study its effects. Consider the following picture:
l(Bib.
#9)
Identifying Sources of Drag
- The Front Radiator ~ 45% (Top) (Bib. #3)
- The Tractor/Trailer separation ~ 20% (Bottom a)
- Rear Drag ~ 20% (Bottom b)
- The undercarriage ~
15%
(Bib. #9)
lAs you can see from the illustrations above the majority of drag produced from a truck rolling down the road is from the wind hitting the large surface area of the radiator and creating a force opposing the velocity of the truck. This accounts for 45% of the overall drag. Then the air flows up across the windshield of the truck and hits the large surface area of the trailer. See the flow of the green smoke in the illustration above. There is turbulent air flow in between the tractor trailer separation by necessity of utility. In other words, the commercial utility of the truck can not be compromised to accommodate a more aerodynamical design. See figure (a) above. There is turbulent flow from the recirculation area in the rear of the trailer. See figure (b) above. Now that the sources of drag have been identified a terminology to define drag quantitatively.
Terminology of Drag Study
- lCd = Drag
- Yaw Angle
Drag is defined as Cd
or the coefficient of drag. It is important to quantify what drag is so
that it can be calculated and studied. The Yaw angle is a
critical parameter. There are comprehensive studies of yaw angle and its
effects that must be considered. If you think about it wind doesn't always
hit your car head on when you drive down the road but instead usually hits your
car at an angle. See the picture below. (Bib. #6)
As you probably know when you are moving down the road at speed the Yaw Angle does not go beyond m 15 degrees. Now we have a basic terminology to discuss and study drag.