What is the most aerodynamic shape?

Aerodynamics Read more from
Chapter Fluids

Golfing has been played for several centuries, but dimpled golf balls have existed for only a hundred years. The dimples in golf balls, first introduced by the Spalding Company in 1908, can double the distance a golf ball can fly. Without the dimples the flow of air is laminar and the ball drags a thin layer of air completely around the golf ball. The dimples break up this air layer, creating turbulence that reduces drag. Golf balls can also experience lift. When hit with a slight backspin, the air passing over the top section of the ball flows in the direction opposite the motion of the ball. This creates low pressure above the ball. On the bottom of the ball the ball’s motion in the same direction as the air and the pressure is higher. According to Bernoulli’s Principle, such a pressure difference provides a lifting force, called the Magnus Force on the ball, giving the ball a few more seconds in flight.

Some think the narrower and more needle-like an object is, the lower its drag force will be. Although a needle-head cuts easily through the wind, the problem emerges at the tail end, where the wind becomes turbulent and forms small eddy currents that hinder the streamline flow of air. The optimum shape depends on the velocity of the object.

For speeds lower than the speed of sound, the most aerodynamically efficient shape is the teardrop. The teardrop has a rounded nose that tapers as it moves backward, forming a narrow, yet rounded tail, which gradually brings the air around the object back together instead of creating eddy currents.

At high velocities, such as a jet airplane or a bullet may travel, other shapes are better. For turbulent flow, the least drag comes from having a blunt end, which intentionally causes turbulence. The rest of the air then flows smoothly over the region of turbulence behind the object.


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