AE301WingPressureDistributionLaboratoryManual - 3 Wing...

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3. Wing Pressure Distribution 3.1. Purposes Measure the pressure profile on the upper and lower surface of a symmetric wing at different air speeds and angle of attack. Learn about Bernoulli’s equation and the interaction of static and dynamic pressures. 3.2. Background A wing is a common device on aircraft and hydro-foil. As a 2-D section, the wing is an airfoil body shape that typically has a rounded nose that widens to a maximum thickness and then the body trails off smoothly to the trailing edge. For example, the NACA0015 airfoil used in this experiment is a symmetric airfoil (as indicated by the 00 digits in the classification) because the top and bottom surfaces are the same shape relative to the mean line that runs down the center of 2-D profile. The digits ‘15' indicate that the thickness of the airfoil is 15% of the overall length or what is called the ‘chord.’ Notice in the figure above that the chord is 4 units (along x) while the thickness is 0.6 units (0.3 on each side of the mean line running along at y=0) and 0.6 is 15% of 4. The NACA name stands for ‘National Advisory Committee for Aeronautics’ that was a government precursor to NASA. For us, the NACA0015 is a well-known wing shape that we can study and compare our results to documented history. 0 0.5 1 1.5 2 2.5 3 3.5 4 -1.5 -1 -0.5 0 0.5 1 1.5
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In the above figure, the air flows left to right. But air can’t go through a solid wing and therefore must move around it. As the air moves around it, near the surface the air does not have the same velocity as the flow in the far-field (far away from the wing). For example, as a plane travels through stationary air, the air is cut and must be deflected from its static state. Relative to the aircraft, our frame of reference is on the wing and the wing is stationary while the air in the far field (all the atmosphere) is traveling by us at the speed of the aircraft. Close to the wing, the flow can be either higher or lower than the air speed. It depends where you are looking on the surface of the wing. At the nose of the wing, the air flow splits so that some of it flows over the top of the wing and some flows under the wing. Since the air is continuous, there must be some limit-point where the flow neither goes up or down. This is called the stagnation point. Actual the air that hits the stagnation point can’t travel through the wing so it does not have any horizontal velocity. Since it is a stagnation point, it does not have any vertical velocity either. Therefore, the stagnation point does not have any air speed. This would be the point that has the maximum pressure from the air. The stagnation pressure is a combination of the static atmospheric pressure and the dynamic pressure that is due to the air moving toward the stagnation point and then stopping at the stagnation point. The dynamic pressure is like a kinetic energy (or enthalpy).
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AE301WingPressureDistributionLaboratoryManual - 3 Wing...

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