Measurement of Pressure Distribution and Lift for an Airfoil

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# Measurement of Pressure Distribution and Lift for an Airfoil - PowerPoint PPT Presentation

Measurement of Pressure Distribution and Lift for an Airfoil. Purpose Test design Measurement system and Procedures Uncertainty Analysis Data Analysis and Discussions . Purpose. Examine the surface pressure distribution Compute the lift force acting on the airfoil. Test Design.

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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

Purpose
• Examine the surface pressure distribution
• Compute the lift force acting on the airfoil
Test Design

Airfoil(=airplane surface: as wing) is placed in test section 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 = Drag

Only 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

Lift force

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

U = free-stream velocity where

r = air density ( temperature), pstagnation stagnation pr

measured at the tip of pitot tube

L = Lift force

b = airfoil span

c = airfoil chord

Pressure Distribution on the Airfoil

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 .

Protractor – angle of attack

Resistance temperature detectors (RTD)

Pitot static probe

Scanning valve

Pressure transducer (Validyne)

Digital Voltmeter (DVM)

Data Acquisition system
A virtual instrument(VI) = Lift is an ADAS is used to calculate the lift coefficient

Data needed:

Total # of points considered

Observation point list

Sampling Rate

Settling Time

Length of each Sample

Conversion Coefficients

Angle of attack

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

Reference Data