Transcript Title
Wind Tunnel Experiments
Investigating the Aerodynamics
of Sports Balls
Team Members:
Colin Jemmott
Sheldon Logan
Alexis Utvich
Advisor: Prof. Jenn Rossmann
Overview
Motivation/Background
Flow Visualization
Calibration
– Pitot tube
– Hot wire anemometer
Wiffle ball instrumentation/experiments
Baseball instrumentation/experiments
Motivation
Previous studies have not produced a
complete understanding of the flowfield
around a spinning baseball
A comprehensive Wiffle ball study has not
been documented before
Background
Reynolds Number:
Re = ρVD/μ
Lift Coefficient:
CL = 2FL/ρU2A
Drag Coefficient:
CD = 2FD/ρU2A
Flow Visualization
Calibration: Velocity Profiles
Measurements were taken to characterize
flow in the test section
Pitot tube measurements were conducted at
heights of 1, 2, 4, 6, 8, 10, and 11 in. and
fan settings of 10, 30, and 50 Hz
– Velocity profiles were constructed from these
measurements
Calibration: Velocity Profiles
10 Hz Velocity Profile
1800
1790
Velocity (ft/min)
1780
1770
1760
1750
1740
1730
1720
1710
1700
1690
0
2
4
6
8
Height (in.)
Front
Middle
Back
10
12
Calibration: Hot-Wire
Anemometer
Device that determines
airflow speed by
measuring the rate of
cooling of a heated
wire.
Measures velocity
fluctuations.
Turbulence level
within tunnel was
found to vary.
Hot Wire Anemometer: 0.3%
Turbulence
Hot Wire Anemometer: 0.5%
Turbulence
Hot Wire Anemometer: 6%
Turbulence
Hot Wire Anemometer: Variance
in Velocity
Stationary Ball Force
Measurements
A nylon rod with strain
gauges mounted on it
was used to measure the
lift and drag forces on
stationary balls.
Two full bridges were
placed on the nylon rod
to measure both axial
and bending effects.
Schematic of Strain Gauge
Device
Schematic of DC Amplifier
Gain ≈ 3000
Amplifying Circuit
Orientation of Ball for Drag
Measurements
Drag Coefficient: Results
The Drag Coefficient of the Wiffle ball was found
to decrease exponentially with respect to the
Reynolds number.
Lift Force
It was discovered that
Wiffle ball would
experience a lift force
if the holes of the ball
were not
symmetrically
distributed about the
horizontal axis.
Lift Force: Results
The magnitude of the lift force seemed to depend
on the angle at which the ball was tilted.
Lift Force: Results
One of the
potential
reasons these
lift forces come
about is due to
the air flowing
into the ball.
Lift Force: Results
The lift force results in the deflection of the wake.
Spinning Baseball Apparatus
Mathematical Breakdown of a
Curveball
Mass
Diameter
Velocity
Angular Velocity
Lift Force
Lift Coefficient
Drag Force
Drag Coefficient
0.32 lb
2.86 in
80 MPH
1800 rpm
0.18 lb
0.20
0.37 lb
0.54
145 g
7.26 cm
36 m/s
30 Hz
0.79 N
1.7 N
-
Forces on an 1800 rpm Baseball
2
Force in Units of the Ball's Weight
1.8
Drag
1.6
Lift
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
20
40
60
Velocity (mph)
80
100
120
Lift on a Spinning Baseball
0.25
Coeffice nt of Lift
0.2
0.15
0.4 E 5
0.8 E 5
1.2 E 5
0.1
1.7 E 5
2.1 E 5
Briggs 2.0 E 5
0.05
Briggs 1.7 E 5
Briggs 1.4 E 5
Briggs 1.0 E 5
0
0
0.2
0.4
0.6
Spin Number (Rw/V)
0.8
1
Coefficient
of Lift by
Spin
Parameter
Comparison
Conclusion
Turbulence levels in the wind tunnel are
satisfactorily low.
Lift force on a Wiffle ball is dependent on
its orientation.
Lift coefficient for a spinning baseball was
found to have stronger dependence on
Reynolds number than previously reported.
Acknowledgements
Sam Abdelmuati
Mike Wheeler
Prof. Carl Baumgaertner
Profs Bright, Cha, and Duron
Prof. Joe King
Prof. Toby Rossmann
Prof. Jenn Rossmann