Pressure Distribution In An Airfoil

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1- Summary

This study is based on the analysis of pressure distribution around a NACA 23015 airfoil section with a flap of length equal to the 30% of the cord at different angles of incidence and flap settings. The experiment was performed in a non –return wind tunnel at a Reynolds number of 4.4×〖10〗^5 and at a Mach number of 0.073.
It is of note that increasing incidence will increase lift produced until the critical angle of attack, where the airfoil stalls; moreover, deploying a flap will increase the maximum lift produced, but will produce drag and cause an early stall.

2-Introduction

The aim of this experiment is to investigate how the pressure difference about the upper and lower surface of an airfoil can affect its aerodynamic performances
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Pressure on the airfoil is measured by tappings along the two surfaces connected to a manometer.The flow velocity is kept constant at 25 m/s and the experiment is conducted in two phases. Firstly, the flap is not deployed and incidence is increased by 5^° steps starting from -5^° to 〖25〗^°. The second phase consist in deploying the flap at 〖-10〗^°, 〖10〗^°, 〖20〗^°, 〖40〗^°, 〖60〗^° and investigate pressure distribution under these conditions. To understand and visualize what is the nature of flow along the airfoil, Plots of C_p against x⁄c are created by collected data. Moreover, nature of the flow along the airfoil has been investigated using a wool tuft, to visualize the flow under every …show more content…
An higher coefficient of lift will reduce the speed and distance necessary for take-off but at the same time it will increase the total drag, causing an earlier stall than a wing with no flap deployed. It is to note that C_D0 increases as the flap is gradually deployed, as shown in graphs 11, 16,20,24,28. Generally speaking, the increase in lift produced by flap is visualized by a steeper suction peak and an earlier separation point. A particular phenomenom is happening in the situation described in Graph 3, a separation bubble is forming. There is a first separation point at x ≃ 0.28, followed by a plateau, with the flow reattaching at x ≃0.63 and separating again at x ≃ 0.82. Here, the highly energetic turbulent flow created after the first separation is reattaching further down on the airfoil, creating the bubble. A separation bubble can be noticed in graph 6 where a negative deflection of the flap (upwards) causes a difference of lift between the front of the airfoil (experiencing a positive lift) and the aft (experiencing a negative lift); this techinique is used by pilot to increase the lift produced Lastly, graph 8, shows that high-lift devices lower the critical angle of attack of an airfoil: at 20° incidence with 40° flap deflection, the airfoil is completely stalled, even if it is still producing

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