The values obtained were then tabulated, graphed and compared. (3) A represents the area of the aerofoil Equation (5) was used to calculate a theoretical value for the lift coefficient. The lift and drag forces obtained for each angle were then plugged into equations (3) and (4) to obtain lift and drag coefficients. Lift and Drag voltage values measured for each angle were recorded and calibration coefficients of 6.7 and 6.4 were used to obtain force Newton values for lift and drag. The protractor of the aerofoil connected to the lift and drag voltmeters was then used to vary the aerofoil’s angle of attack from 0° to 20°. (2) Airflow velocity calculated was 14.68 m/s. (1) was calculated to be 137,34 kPa was the plugged into equation (2) to determine the velocity of the airflow in the wind tunnel. The difference in the fluid level of two manometers was then used to determine the stagnation deflection, which was found to be 14mm was then plugged in equation (1) to calculate the difference between atmospheric and stagnation pressure. To determine the velocity of airflow in the tunnel, both aerofoils (assumed to be sufficiently apart to not be affected by any disturbances) were set at an angle of attack of 0°. The effect this had on the manometers was observed. Methodologyįirst, the protractor on which the aerofoil with tappings attached manometers was used to vary the aerofoil’s angle of attack. The pictures represent the pressure distributions above and below the air foil when the angle of attack is 0°, at stall, and after stall. The manometers on the left represent the pressure sensors on the bottom while the ones on the right represent those on the top. Manometers connected to pressure tappings on the second aerofoil. Both aerofoils were mounted on protractors that rendered it possible to change their angle of attack.
#Airfoil pressure distribution series
The other one had pressure tappings above and below it connected to the series of manometers. One of the aerofoils was lined with nylon tufts and had force balance amplifiers connected to voltmeters enabling measurements for lift and drag to be taken. The apparatus used for this lab experiment consists of two NACA0015 aerofoils placed one in front of the other in a wind tunnel. After stall angle however, a wake is formed above the aerofoil causing air above the aerofoil to recirculate to the front. The theory also predicts that up to stall angle, the air circulation around the aerofoil is normal, it travels above and below the aerofoil from front to back. This pattern continues until the aerofoil reaches a point where the increase in angle of incidence no longer produces increase in lift force, this position is called the Stall. However, as the angle of attack increases, the rate of increase of lift force decreases. As the angle of incidence increases, the point of flow separation moves forward towards the trailing edge of the aerofoil thus increasing the lift force. This generates higher pressures below the aerofoil and results in a net lift force that varies with the its angle of attack vis a vis airflow. This air circulation pattern results in the air above the aerofoil to have higher velocities than that below it. The shape of the aerofoil results in a particular air circulation pattern around it. When air is blown over an aerofoil, it separates into two distinct sets of streamlines above and below it separated by a dividing streamline. An attempt was made to explain any discrepancies between experimental and theoretical values. The experimental lift force the aerofoil experienced when positioned at different angles of attack was then compared with theoretical values. This was done by recording the lift and drag forces the aerofoil experienced when positioned at different angles of attack. This report aims to investigate the effect the angle of attack of an aerofoil has on the air flow around it.
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