 Purpose  Test design  Measurement system and Procedures  Uncertainty Analysis.

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Measurement of Pressure Distribution and Lift for an Airfoil

AOA, and Pressure taps positions

PurposeExamine 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 forPressure coefficientLift coefficientTest Design

Facility consists of: Closed circuit vertical wind tunnel. AirfoilTemperature sensor Pitot tube Load cell Pressure transducer Hot wire anemometer Automated data acquisition system

Measurement systemsInstrumentationProtractor angle of attackResistance temperature detectors (RTD)Pitot static probe velocity Scanning valve scans pressure portsPressure transducer (Validyne) Digital Voltmeter (DVM)Load cell lift and drag force

Measurement systems

Hot-wire anemometryCorrelates velocity and voltageSurvey of velocity in wake region is preformedLower velocities are found directly downstream of airfoilHigher velocities are located far above and below airfoilApply momentum flux equations to calculate drag force

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 and drag forcesThe 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

Calibration of load cell

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 programProgram outputCurve fitting methodData acquisition

Setting up the initial motor speedVisualization of wind tunnel conditionsData acquisition (contd.)Data needed:Observation point listSampling RateSettling TimeLength of each SampleAngle of attack

Airfoil pressure visualization Calculation of lift force

Program to measure lift force in voltsCalculation of drag forceProgram to measure velocity in volts

Uncertainty analysis

Uncertainty analysisPressure coefficientLift coefficient

Benchmark data a) Distribution of the pressure coefficients for = 0, 6, 13, 16 and Re = 300,000; , Benchmark data

Benchmark data continuedReference data for CL Reference data for CD

Velocity profiles

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