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