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Aircraft
Published in Milica Kalić, Slavica Dožić, Danica Babić, Introduction to the Air Transport System, 2022
Milica Kalić, Slavica Dožić, Danica Babić
If the wing is cut with a plane that is parallel to the direction of the air flow and perpendiculars to the horizontal plane, an aerofoil is obtained. In other words, the cross section of the wing is the aerofoil. An aerofoil represents an aerodynamically shaped body that produces an aerodynamic reaction (lift) perpendicular to its direction of motion, for a small resistance (drag) force on that plane. An aerofoil is defined by the suction surface (camber upper surface), pressure surface (camber lower surface), the leading edge, the trailing edge, and the chord line, Figure 2.3. The chord is defined as the distance from the leading edge to the trailing edge and generally varies along the span (McCormick 1995). The leading edge is the first point of the aerofoil or the wing line that the air flow encounters. One part of the air flow passes over the upper and the other below the lower surface. The shape of the aerofoil takes advantage of the air’s response to certain physical laws. Because of the aerofoil shape, the air flow rate is higher on the camber upper surface of the wing due to the longer the distance that it crosses. Therefore, an area of lower pressure relative to the camber’s lower surface is produced on the camber’s upper surface. The lift force is a result not only of pressure differences between upper and lower wing surfaces, but also of the angle of air stream attack, aerofoil shape, air density, and air stream velocity.
Noise emissions from commercial aircraft
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
Slats are high-lift devices installed on the wing leading edge to enhance the wing's lift by allowing it to operate at higher angles of attack at low flight speeds. Slats are deployed during landing to allow the aircraft to operate close to its stall speed. As shown in Figure 1.14, when slats are deployed a gap is generated between the slats and the main wing, which allows a highly unsteady flow to be established inside the slat cavity called the slat cove. A main feature of that flow is the cove vortex whose impingement on the leeward face of the cove is thought to be a major source of slat noise. Added to this source is the vortex shedding that occurs at the slat trailing edge and, potentially, the unsteady flow interactions with the main wing's leading edge. Slat noise is broadband but more directional than the landing gear noise with its dominant radiation in a quadrant directly below and just to the aft of the aircraft.
Airborne dust-induced performance degradation in NREL phase VI wind turbine: a numerical study
Published in International Journal of Green Energy, 2023
J. Zare, S. E. Hosseini, M. R. Rastan
Diab et al. (2015) explored dust accumulation on a number of widely used airfoil sections in the wind turbine industry by NACA, NREL, and DU, showing how passing time changes the blade profile and correspondingly the aerodynamic parameters. The results show that although the dust accumulation percentage is contingent on the blade type, the time and adverse effects have almost a linear rate. They suggested installing a leading edge slat to mitigate the adverse influences of dust contamination. Khalfallah and Koliub (Khalfallah and Koliub 2007) experimentally analyzed the effect of surface roughness due to dust accumulation on the performance of wind turbines. Moreover, the mechanism of dust accumulation was discussed. They observed that the roughness from the chord line toward the leading edge on blades of a stall-regulated, horizontal axis 300 kW wind turbine changes from 5% to 20%. Increasing the blade surface roughness generally reduces the effectiveness of the airfoil and the power output. However, the deterioration depends on the size and nature of the roughness, Reynolds number, and airfoil type. The 2D numerical study of Li et al. (2010) on the DU 95-W-180 airfoil determined the critical roughness height of a wind turbine airfoil as 0.5 mm. The lift and drag coefficient curves of the airfoil with sub-critical roughness decreases and increases, respectively. Beyond the critical value, the rate of variations are decelerated.
Evaluation of novel-objective functions in the design optimization of a transonic rotor by using deep learning
Published in Engineering Applications of Computational Fluid Mechanics, 2021
A. Zeinalzadeh, M.R. Pakatchian
The design space consists of 37 geometrical variables (), seven objective functions and five constraints (V1, V2, V14, V16, V18). Figure 7 shows a boxplot of non-dimensional range of the involved variables from hub to shroud of selected airfoils. In this figure, Vi stands for where (), and for where . For instance, (V1, V2) implies the (x, y) related to the first control point of the thickness distribution line. There are specified variables that are held constant, as determined by zero values in Figure 7, due to initial design considerations and tangency requirements of the Bezier representation; for example, (V7, V8) and (V5, V6), and (V15, V16) and (V17, V18) conform to this requirement. V14, V16, and V18 are related to the maximum thickness of the airfoil and are considered to be constant during optimization. The constants V25 and V27 coincide on the leading edge and the trailing edge, respectively, and determine the chord of the airfoil. Note that the meridional chord is held constant in order to meet the requirements of spacing between the rotor and stator of the first stage. This spacing varies from hub to shroud respectively in the basic design. The fill factor and outflow angle are allowed to vary in a determined bound, in case thickening of the blade at the hub or even at the shroud are required.
Understanding pilot response to flight safety events using categorisation theory
Published in Theoretical Issues in Ergonomics Science, 2019
The crew also exceeded the speed limit for the wing slat and flap devices during the go-around, and this caused a variety of unusual system behaviour. They were not sure if they had exceeded the flap speed limits, despite experiencing an 18 knot and 47 knot exceedance at two different flap settings. Flap speed exceedances are not practiced as they are usually a consequence of inadvertent mismanagement of energy and flightpath. As a result the crew had no exemplar events to compare with their predicament or help with recognition. They then experienced two separate caution messages, ‘LE (leading edge) SLAT DISAGREE’ and ‘TE (trailing edge) FLAP DISAGREE’, partly the result of the speed exceedance and partly due to the incorrect execution of the checklist. These failure messages are conceptually similar, so prone to confusion, a situation exacerbated by their subsequent disappearance brought about by switching to alternate flap control. This illustrates how connecting failure messages with correct checklist selection can be difficult in non-typical scenarios, especially where system behaviour is less transparent and informative than previous flight crew encounters. The difficulty the crew had in managing these events was attributed to their unfamiliarity with this type of malfunction and the associated checklist. The infrequency of exemplar slat/flap events leads to weaker conceptual knowledge; a classic gradient that damaged the crews understanding of the situation and their behaviour. Unfortunately, a great number of flight safety events show this characteristic.