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Measurement of Pressure Distribution and Lift for

an Airfoil

Purpose

Test design

Measurement system and Procedures

Uncertainty Analysis

Data Analysis and Discussions

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Purpose

Examine the surface pressure distribution

Compute the lift force acting on the airfoil

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Test Design

Airfoil(=airplane surface: as wing) is placed in testsection of a wind tunnel where a flowing fluid (air)is operating. This airfoil is exposed to:

Forces acting normal to free stream = Lift

Forces acting parallel to free stream = DragOnly two dimensional airfoils are considered:

Top of Airfoil:

The velocity of the flow is greater than the free-stream.

The pressure is negative

Underside of Airfoil:

Velocity of the flow is less than the the free-stream. The pressure is positive

This pressure distribution contribute to the lift

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AOA, and Pr Taps Positions

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Lift forceThe lift force L is determined by integration

of the measured pressure distribution over the airfoils surface.

It is expressed in a dimensionless form by the pressure

coefficient Cp where

pi = surface pressure measured, p = pressure in the free-stream

U = free-stream velocity wherer = air density ( temperature), pstagnation stagnation pr

measured at the tip of pitot tube

L = Lift force

b = airfoil span

c = airfoil chord

2

2

1

U

ppC ip

r

r

ppU

stagnation2

bcULCL 22

r

dsppLs

sin

cU

dspp

C sL2

2

1

sin

r

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Pressure Distribution on the Airfoil

In this experiment, the liftforce, L on the Airfoil willbe determined byintegration of themeasured pressuredistribution over theAirfoils surface. Thefigure shows a typicalpressure distribution onan Airfoil and itsprojection .

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Data Acquisition system

Airfoil Model

Pitot Tube(Free

Stream)

Pressure Taps

Bundle oftubes

Digitali/o

A/DBoards

SerialComm.(COM1)

Software- Surface

Pressure- Velocity- WT Control

PC

ScanivalvePosition

Circuit (SPC)

RTD

MetrabyteM2521Signal

Conditioner

ScanivalveSignal

Conditioner

(SSC)

ScanivalveController

(SC)

Scanivalve

PressureTransducer

(Validyne)

DigitalVoltimeter

(DVM)

PressureInput

Protractor angle of attack

Resistance temperature detectors (RTD)

Pitot static probe

Scanning valve

Pressure transducer (Validyne)

Digital Voltmeter (DVM)

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Measurement System and data reduction

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ADAS

A virtual instrument(VI) =Lift is an ADAS is used tocalculate the liftcoefficient

Data needed: Total # of points considered

Observation point list

Sampling Rate

Settling Time

Length of each Sample Conversion Coefficients

Angle of attack

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Reference Data

References plots with 6

different angles of attack:

0 Group 1,2 4 Group 3,4

6 Group 5,6

8 Group 7,8 12 Group 9,10

14 Group 11

x/c

020406080100

Cp

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

AOA=0

x/c

020406080100

Cp

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

AOA=8

x/c

020406080100

Cp

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

AOA=4

x/c

020406080100

Cp

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

AOA=6

x/c

020406080100

Cp

-3.0

-2.5-2.0

-1.5

-1.0

-0.5

0.0

0.51.0

1.5

2.0

2.5

3.0

AOA=12

x/c

020406080100

Cp

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

A0A=14