Pressure Distribution In An Airfoil
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.
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 …show more content…
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