62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009;
Minneapolis, Minnesota
Session BW: Mini-Symposium on Fluid Dynamics of Sports
10:30 AM–12:40 PM,
Sunday, November 22, 2009
Room: 208A-D
Chair: Kyle Squires, Arizona State University
Abstract ID: BAPS.2009.DFD.BW.5
Abstract: BW.00005 : Fluid Mechanics of Cricket and Tennis Balls
12:14 PM–12:40 PM
Preview Abstract
Abstract
Author:
Rabindra D. Mehta
(Sports Aerodynamics Consultant, Mountain View, California)
Aerodynamics plays a prominent role in defining the flight of a
ball that is struck or thrown through the air in almost all ball
sports. The main interest is in the fact that the ball can often
deviate from its initial straight path, resulting in a curved, or
sometimes an unpredictable, flight path. It is particularly
fascinating that that not all the parameters that affect the
flight of a ball are always under human influence. Lateral
deflection in flight, commonly known as swing, swerve or curve,
is well recognized in cricket and tennis. In tennis, the lateral
deflection is produced by spinning the ball about an axis
perpendicular to the line of flight, which gives rise to what is
commonly known as the \textit{Magnus effect.} It is now well
recognized that the aerodynamics of sports balls are strongly
dependent on the detailed development and behavior of the
boundary layer on the ball's surface. A side force, which makes a
ball curve through the air, can also be generated in the absence
of the Magnus effect. In one of the cricket deliveries, the ball
is released with the seam angled, which trips the laminar
boundary layer into a turbulent state on that side. The turbulent
boundary layer separates relatively late compared to the laminar
layer on the other side, thereby creating a pressure difference
and hence side force. The fluid mechanics of a cricket ball
become very interesting at the higher Reynolds numbers and this
will be discussed in detail. Of all the round sports balls, a
tennis ball has the highest drag coefficient. This will be
explained in terms of the contribution of the ``fuzz" drag and
how that changes with Reynolds number and ball surface wear. It
is particularly fascinating that, purely through historical
accidents, small disturbances on the ball surface, such as the
stitching on cricket balls and the felt cover on tennis balls are
all about the right size to affect boundary layer transition and
development in the Reynolds numbers of interest. The fluid
mechanics of cricket and tennis balls will be discussed in detail
with the help of latest test data, analyses and video clips.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.DFD.BW.5