Knee-Down Aerodynamics

KNEE-DOWN AERODYNAMICS

WHAT YOU SEE HERE IS computational fluid dynamics animation of airflow over a Yamaha YZF-R1 and its rider. It was created by Advantage CFD. an English firm (www.advantage-cfd.co.uk). using software from the Fluent Corporation of Lebanon. New Hampshire (www.fluent.com).

One hundred years ago, lift and drag were purely experimental subjects. The Wright brothers built their miniature wind tunnel and sophistication grew from there. Applied math ematicians analyzed specific situations like the flow of air ov er wings or prop blades.

In the wind tunnel, airflow was visualized by “smoke rakes”-bars with many outlets from which streams of smoke trailed over test objects to make flow phenomena v isible. Tufts of thread were taped to vehicle surfaces and observed to reveal where drag-increasing flow separations occurred.

Aero cook books, like Hoemer’s famous big white volumes, provided rules of thumb for estimating the drag of messy shapes that were beyond manual calculation-radar arrays or landing wheels, for example.

Then came the computer. Com-

plex shapes

A could be digi-

tized and flow around

broken

down

into elements. Then, a computer could apply the basic equations of viscous fluid flow, element by element, and crunch out the flow field. This is CFD. the uses of which are now expanding beyond av iation to a variety of less obvious tasks like analyzing under-hood airflow in cars and forces on a motorcycle in midcorncr.

Like any tool, CFD software requires skill in its use. Some fudging of the treatment of turbulence (most mysterious of subjects) and craftsmanship in preparing the computational mesh are required to get the programs to solve problems rather than give meaningless infinities.

In the case of the Rl, the goal was to find possible aerodynamic means to increase cornering speed. Sources of lift, which reduces tire grip, were identified, and an improved fairing shape was determined-one with a fuller shape where it comes closest to the road surface. A corner speed increase of 0.5 mph resulted. Although this is only one-third of a percent of the corner speed of 150 mph. over a one-hour race, a 5-second margin of victory is a mere 'Ath of a percent. Of course, all corners aren't taken at 150 mph. but you get the point.

Kevin Cameron