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

AOA, and Pr Taps Positions

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 C p where pi = surface pressure measured, p = pressure in the free-stream U = free-stream velocity where  = air density ( temperature), p stagnation 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.

Data Acquisition system  Protractor – angle of attack  Resistance temperature detectors (RTD)  Pitot static probe  Scanning valve  Pressure transducer (Validyne)  Digital Voltmeter (DVM)

Measurement System and data reduction

ADAS 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

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