measurement of pressure distribution and lift for an airfoil purpose test design measurement...
TRANSCRIPT
Measurement of Pressure Distribution and Lift for an
Airfoil
PurposeTest designMeasurement system and Procedures
Instrumentation Data reduction Data acquisition
Uncertainty Analysis
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
Test DesignTest Design
Facility consists of: Closed circuit vertical wind tunnel. Airfoil Load cell Temperature sensor Automated data acquisition system
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
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
AOA, and Pressure taps positions
AOA, and Pressure taps positions
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 .
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,,,,
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
Data acquisitionData acquisition
Setting up the initial motor speed Visualization of wind tunnel conditions
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
Calculation of lift forceCalculation of lift force
Program to measure lift force in volts
Uncertainty analysisUncertainty analysis
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
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