# measurement of pressure distribution, drag, lift , and velocity for an airfoil

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Measurement of Pressure Distribution, Drag, Lift , and Velocity for an Airfoil. Purpose Test design Measurement system and Procedures Uncertainty Analysis. Purpose. Examine the surface pressure distribution and wake velocity profile on a Clark-Y airfoil - PowerPoint PPT Presentation

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• PurposeTest designMeasurement system and ProceduresUncertainty Analysis

• PurposeExamine the surface pressure distribution and wake velocity profile on a Clark-Y airfoilCompute the lift and drag forces acting on the airfoilSpecify the flow Reynolds numberCompare the results with benchmark dataUncertainty analysis forPressure coefficientLift coefficient

• Facility consists of: Closed circuit vertical wind tunnel. AirfoilTemperature sensor Pitot tubes Load cell Pressure transducerAutomated data acquisition system

• 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 = LiftForces 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 free-stream. The pressure is positiveThis pressure distribution contribute to the lift

• InstrumentationProtractor angle of attackResistance temperature detectors (RTD)Pitot static probe velocity Vertical Pitot probe traverseScanning valve scans pressure portsPressure transducer (Validyne) Digital Voltmeter (DVM)Load cell lift and drag force

• AOA, and Pressure taps positions

• Data reduction In this experiment, the lift force, L on the Airfoil will be determined by integration of the measured pressure distribution over the Airfoils surface. The figure shows a typical pressure distribution on an Airfoil and its projection .

• Data reduction Calculation of 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-streamThe lift force is also measured using the load cell and data acquisition system directly.

U = free-stream velocity, r = air density (temperature), pstagnation = stagnation pressure measured at the tip of the pitot tube, L = Lift force, b = airfoil span, c = airfoil chord

• Data reduction The drag force, D on the Airfoil will be determined by integration of the momentum loss found by measuring the axial velocity profile in the wake of the Airfoil. The figure shows how the wake of the airfoil affects the velocity profile.

• Data reduction Calculation of drag forceThe lift force D is determined by integration of the momentum loss found from the velocity profile measurement. The velocity profile u(y) is approximated by measuring ui at predefined locationsThe drag force is also measured using the load cell and data acquisition system directly.

U = free-stream velocity, r = air density (temperature), pstagnation = stagnation pressure measured at the tip of the pitot tube, D = Lift force, b = airfoil span, c = airfoil chord

• Calibration programProgram outputCurve fitting method

Chart1

0

0.295

0.415

0.765

1.31

1.635

Fzavg

Volts

Mass

Lift

Sheet1

Force CalibrationInitial VWT load cell calibration done by DOH and MAW on 20031023

10/23/03

2:57 PM

VoltsL(n)L(ghosh)

Mass [kg]Lift [V]LiftSD [V]Drag [V]DragSD [V]VoltsFitted KgFitted N-0.1422.4116570464.76448156

0-0.02710.0046-0.03510.00430.000-0.0053-0.0524-0.1983.5693233746.94983564

0.105-0.07670.0079-0.03420.0156-0.0500.10000.9809-0.3667.04232235813.50589788

0.11-0.07790.0042-0.04020.0042-0.1000.20542.0142-0.2173.9621030217.69129506

0.195-0.11830.004-0.0470.0052-0.1500.31083.0475-0.3496.69088793712.84248682

0.3-0.16740.0034-0.06410.0048-0.2000.41614.0807-0.713.946975126.539974

0.79-0.39310.0032-0.09550.0053-0.2500.52155.1140-0.523854-0.776952

1.54-0.75960.0036-0.16950.0059-0.3000.62696.1473-0.523854-0.776952

Sheet1

Lift (volts)

Mass (kg)

VWT Initial Force Calibration

Lift (kg) = -2.1073* Volts - 0.0534R2 = 0.9998

Sheet2

mass (kg)Fy1Fy2avg FyFz1Fz2avg Fz

0-0.015-0.027-0.021-0.015-0.015-0.015

0.295-0.163-0.142-0.1525-0.093-0.111-0.102

0.415-0.22-0.186-0.203-0.102-0.142-0.122

0.765-0.391-0.322-0.3565-0.188-0.238-0.213

1.31-0.669-0.518-0.5935-0.316-0.381-0.3485

1.635-0.808-0.669-0.7385-0.395-0.465-0.43

mass (kg)avg Fy

0-0.021

0.295-0.1525

0.415-0.203

0.765-0.3565

1.31-0.5935

1.635-0.7385

Sheet2

Fzavg

Volts

Mass

Lift

Sheet3

Fy1

Fy2

Fyavg

Volts

mass

Drag

• Setting up the initial motor speedVisualization of wind tunnel conditions

• Data acquisition (contd.)Data needed:Observation point listSampling RateSettling TimeLength of each SampleAngle of attackAirfoil pressure visualization

• Program to measure lift force in volts

• Program to measure velocity in volts

• Uncertainty analysis

• Pressure coefficientLift coefficient

• Benchmark data

Distribution of the pressure coefficients for = 0, 4, 8, 16 and Re = 300,000

• Benchmark data continuedReference data for CL Reference data for CD

• ePIVMeasurements of complete flow field with a small Clark-YRe1000 Chord length 20 mmAoA of 0 and 16Plot the followingContour of velocity magnitudeVector fieldStreamlinesTwo models: AoA 0 and 16

• ePIV-Post Processing StreamlinesContour of velocity magnitudeVelocity vectors

• ePIV Post Processing continuedFlow conditionsRe 1000AoA = 16

PIV settingBrightness = 35Exposure = 100Gain = 100Frames = 9Window size = 30Shift size = 15PIV pairs = 9

AirfoilWakeWallWallFlow

• ePIV AnalysisFlow featuresOptical hindrance

Fast moving flowLow pressure region

Stagnation points

Slow moving flowHigh pressure region

• ePIV CFD ComparisonePIV CFD

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