Bernoulli's in a Building
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Transcript of Bernoulli's in a Building
Examining Bernoulli’s Principle
through the McKee Breezeway
Measuring the Effects of Building Construction on Wind FlowThrough a Structure
Ross Kononen, Keri Bowling, Nick Horianopoulos, and Matt Nolen
Scientific Observation• McKee Hall’s breezeway
– Uncomfortable!– Cold– Windy
Scientific Observation- Ross Kononen noticed wind while
skateboarding
Scientific Question
• Why does the wind velocity appear to increase inside of the McKee breezeway?
• Probable Cause: Dynamic of wind changed by some property of building
Hypothesis• If the McKee Hall Breezeway acts as
a venturi, then: 1. High pressure will exist in
front of and behind the breezeway
2. Low pressure will exist within the breezeway
3. The velocity within the breezeway will increase due to the pressure differential between the outside and the inside of the breezeway
Supporting Literature• Blocken B, Stathopoulos T, Carmeliet J. (2008) Wind environmental
conditions in passages between two long narrow perpendicular buildings. Journal of Aerospace Engineering – ASCE 21(4): 280-287
• Gaimbattista, A., Richardson, B., & Richardson, R.C. (2010) Physics (2nd ed.). New York, NY: McGraw-Hill Companies, Inc.
• Heim, D., and Klemm, K., (2009) LOCAL WIND AND RAIN CONDITIONS IN SEMI-CLOSED NARROW CORRIDORS BETWEEN BUILDINGS , Eleventh International IBPSA Conference, Glasgow, Scotland July 27-30, 2009 1745 – 1752.
• McIlveen, J. F. R., (2002) The everyday effects of wind drag on people, Weather , Vol. 57, pp. 410-417
• Serway, R.A., Faughn, J.S. Vuille, C., Bennett, C.A., (2006) College Physics, (7th ed.), Belmont, CA: Thomas Brooks/Cole, Ch. 6, 160-164
• APB Foundation. (1998). Session 9, Part B: Surface Area and Volume. Retrieved November 04, 2011, from Learning Math: Measurement: http://www.learner.org/courses/learningmath/measurement/session9/solutions_b.html#b8
Examination of Space
}
Examination of SpaceInitial Speed 2.995 m/sFinal Velocity 0. 939 m/s
Outside headwind 2.995 m/sInside headwind???
8.3mIgnored:
• Friction (ground, wheels, Ross’ hair)
• Rotational losses• Vectors
from motion equations
4.25s
an estimate
We thought we could model a value for the wind slowing Ross down
Estimation of Wind Speed
if mVmVptF Used momentum equation to determine force required to slow Ross down:
t
pFav
s
mKg
7.238
s
m 939.0 kg 116.1
s
m 2.995 kg 116.1
Nssm
Kg2.56
25.4
7.238
Estimation of Wind Speed
N)(in force drag 2
2
AvCd
Estimation of Drag Force (modeled at 0.50)
Where:
Air Density, usually 1.2 kg/m3
dC Coefficient of Drag, 0.5 (McIlveen 2002)
A Area, m2
v Velocity in m/s56.2N 4247.050.0
2
2.122
3
vmmKg
s
m01.18
s
m 2.995 of headwind original
s
m21.0v
known from momentum equation
Estimation of Wind Speed
Estimation of Drag Force (modeled at 0.85)
Where:
Air Density, usually 1.2 kg/m3
dC Coefficient of Drag, 0.85 (Engineering Toolbox, 2011)
A Area, m2
v Velocity in m/s56.2N 4247.085.0
2
2.122
3
vmmKg
s
m11.13
s
m 2.995 of headwind original
s
m.161v
known from momentum equation
N)(in force drag 2
2
AvCd
Rosstimation• Ross is 6’4” or 193 cm• Make a square with arms out• Fingertip-fingertip distance is
roughly your height• Square that value, 3/5ths = surface
area (Annenberg Foundation 2011)•Only 19% surface area
exposed to relative wind•Side profile 4247cm2 or 0.4247m2
{19%
Physicist Approved!
• Dr. Matthew Semak• Numbers and physics “make sense”
So to review…
• 13-18 m/s (46 kph to 65 kph) gusts slowing a skateboarder in 8m and 4 ¼ seconds inside McKee Breezeway
• We should expect values somewhat close to these if hypothesis = valid (a 1:~7 down to a 1:4 ratio of speed inside to speed outside)
• We began our research!
Data Collection
• We collected data…
Data Collection
• Three data collectors• Data taken:
– 10 readings– 30 seconds– 5 minutes total
Data Collection
Equidistant, along centerline
Data Collection• We used calibrated anemometers• Precision to the 1/10th m/s
Collection Problem
• Notes– Surprisingly few windy days
• 10 attempts, 3 conditions of observable data
Collection Problem• Unique weather conditions
– When in Colorado is it not windy during Fall?
– Four years history – winds low in 2011!
• Wind mostly came from out of NNE– Also unusual
• Last reading came out of SSW!– Low wind readings outboard– High wind readings inside– Supporting?
Collection Problem
October 2011
October 2010
Findings
1 2 3 4 5 6 7 8 9 100
2
4
6
8
10
12
14
Observations on Oct. 20, 2011
Trial Number
Win
d V
elo
city
(km
/h)
1 2 3 4 5 6 7 8 9 100
2
4
6
8
10
12Observations on Oct. 25, 2011
SE Side of McKee
Breezeway Center
NW Side of McKee
Trial Number
Win
d V
elo
city
(km
/h)
1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8Observations on Nov. 6, 2011
Trial Number
Win
d V
elo
city
(km
/h)
Findings
Mostly shows higher wind values outside of breezeway
than inside!
AHHHHHH!
SE side Breezeway NW side0
1
2
3
4
5
6
7
8
9
Average Wind Velocities from Measurement Points
Oct. 20
Poly-nomial (Oct. 20)
Oct. 25
Measurement Point
Ave
rag
e W
ind
Vel
oci
ty (
km/h
)
FindingsDo we reject hypothesis?
•Majority of observations do not support hypothesis•Curious conditions cause suspicion•Not enough data able to be taken to support conclusion either way
•Why??
Analysis•What we think happened:
High pressure(low speed)
Low
pre
ssur
e
(hig
h sp
eed)
1
Low
pre
ssur
e
(hig
h sp
eed)
1
Potential Sources of Error
• Trees• Measurement error
– Face into wind?
• Oddball weather conditions
October 2011
October 2010
Applying this to classroom•Teach learners that science is
complex•Object lesson: wind patterns, historical data•You may have to make many observations to prove or disprove hypothesis•Inquiry based projects promote group work skills•You may not just get different results, you may get results that don’t match observations•Knowledge of Bernoulli’s Principle can help students make better decisions during the course of their lives