measurement of pressure distribution and lift for an airfoil purpose test design measurement...
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Measurement of Pressure Distribution and Lift for an
Airfoil
PurposeTest designMeasurement system and Procedures
Instrumentation Data reduction Data acquisition
Uncertainty Analysis
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PurposePurpose
Examine the surface pressure distribution on a Clark-Y airfoilCompute the lift and drag forces acting on the airfoilSpecify the flow Reynolds numberCompare the results with benchmark dataUncertainty analysis for
Pressure coefficientLift coefficient
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Test DesignTest Design
Facility consists of: Closed circuit vertical wind tunnel. Airfoil Load cell Temperature sensor Automated data acquisition system
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Test Design (contd.)Test Design (contd.)
Airfoil (=airplane surface: as wing) is placed in test section of a wind tunnel with free-stream velocity of 15 m/s. This airfoil is exposed to:
Forces acting normal to free stream = Lift Forces acting parallel to free stream = Drag
Only two dimensional airfoils are considered:Top of Airfoil: The velocity of the flow is greater than the free-stream. The pressure is negativeUnderside of Airfoil: Velocity of the flow is less than the the free-stream. The pressure is positiveThis pressure distribution contribute to the lift
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Measurement systemsMeasurement systems
Instrumentation Protractor – angle of attack Resistance temperature detectors (RTD) Pitot static probe – velocity Scanning valve – scans pressure ports Pressure transducer (Validyne) Digital Voltmeter (DVM) Load cell – lift and drag force
Airfoil Model
Pitot Tube(Free
Stream)
Pressure Taps
Bu nd le o ftu bes
Digita li/o
A /DBo ards
SerialCo m m .(C O M 1)
So ftw are- Su rface Pressu re- Ve lo c ity- W T C on tro l
PC
ScanivalvePo sition
C ircu it (S PC)
RT D
M etrabyteM 2521Sign al
Co nd itio ner
ScanivalveSign al
Co nd itio ner(S SC)
ScanivalveCo ntroller
(S C)
Scanivalve
PressureTransdu cer(Valid yne)
D igita lVo ltim eter
(D VM )
PressureIn p ut
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AOA, and Pressure taps positions
AOA, and Pressure taps positions
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Data reductionData reduction
In this experiment, the lift force, L on the Airfoil will be determined by integration of the measured pressure distribution over the Airfoil’s surface. The figure shows a typical pressure distribution on an Airfoil and its projection .
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Data reduction Data reduction
Calculation of lift and drag forces The lift force L is determined by integration of the measured
pressure distribution over the airfoil’s surface. It is expressed in a dimensionless form by the pressure
coefficient Cp where, pi = surface pressure measured, = P pressure in the free-stream
The lift force is also measured using the load cell and data acquisition system directly.
U = free-stream velocity, = air density ( temperature), pstagnation = stagnation pressure measured at the tip of the
pitot tube, L = Lift force, b = airfoil span, c = airfoil chord
cU
dspp
C sL
2
21
sin
2
21
U
ppC ip
ppU stagnation2
bcU
LCL 2
2
dsppLs
sin
bcU
DcbUDCD 2
2,,,,
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Calibration of load cellCalibration of load cell
Lifty = -3.9781x - 0.0792
R2 = 0.9992
-0.50
0.51
1.52
-0.6 -0.4 -0.2 0
Volts
Mas
s Fzavg
Linear(Fzavg)
mass (kg) Volts
0 -0.021
0.295 -0.1525
0.415 -0.203
0.765 -0.3565
1.31 -0.5935
1.635 -0.7385
Calibration program
Program output
Curve fitting method
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Data acquisitionData acquisition
Setting up the initial motor speed Visualization of wind tunnel conditions
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Data acquisition (contd.)Data acquisition (contd.)
Data needed: Observation point list Sampling Rate Settling Time Length of each Sample Angle of attack
Airfoil pressure visualization
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Calculation of lift forceCalculation of lift force
Program to measure lift force in volts
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Uncertainty analysisUncertainty analysis
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Uncertainty analysisUncertainty analysisPressure coefficient Lift coefficient
),,( UppfC ip
222CpCpCp PBU
2)(
2)(
2
1
22
ppippii
j
iiCp BBB
2_
2
Upp
C
i
pppi
MSP CpCp 2
),,,,( cUppfC iil
222CLCLCL PBU
2)(
2)(
2
1
22
ppippii
j
iiCL BBB
MSP CLCL 2
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Benchmark dataBenchmark data
a) Distribution of the pressure coefficients for = 0, 6, 13, 16 and Re = 300,000; , Benchmark data
Reference data for CL
Reference data for CD
Benchmark data for pressure coefficient for AOA = 0
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100
x/c
Co
eff
cie
nt
of
pre
ss
ure
(C
p)
AOA = 0
Benchmark data for pressure coefficient for AOA = 6
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100
x/c
Co
eff
cie
nt
of
pre
ss
ure
(C
p)
AOA = 6
Benchmark data for pressure coefficient for AOA = 16
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100
x/c
Co
eff
cien
t o
f pre
ss
ure
(Cp
)
AOA = 16
Benchmark data for lift coefficient
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 5 10 15 20 25 30 35
Angle of attack (AOA)
Lif
t c
oe
ffic
ien
t (C
l)
Benchmark data for drag coefficient
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 5 10 15 20 25 30 35
Angle of attack (AOA)
Dra
g c
oef
ficie
nt (
Cd
)
Benchmark data for pressure coefficient for AOA = 13
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100
x/c
Co
effc
ien
t o
f p
ress
ure
(C
p) AOA = 13