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Unsteady Aerodynamics
Published in Rama B. Bhat, Principles of Aeroelasticity, 2018
Consequently, unsteady-aerodynamic theories need to account for at least three separate physical phenomena, as follows: In view of the airfoil’s unsteady motion relative to the air, the relative wind vector is not fixed in space. The changing direction of the relative wind changes the effective angle of attack and thus changes the lift.The airfoil motion disturbs the flow and causes a vortex to be shed at the trailing edge (Fung 1955). The downwash from this vortex, in turn, changes the flow that impinges on the airfoil. This unsteady downwash changes the effective angle of attack and thus changes the lift.The motion of the airfoil accelerates air particles near the airfoil surface, thus creating the need to account for the resulting inertial forces (although this “apparent-inertia” effect is less significant than that of the shed vorticity). The apparent-inertia effect does not change the angle of attack but it does, in general, affect both lift and pitching moment.
A Search for Meaning: A Case Study of the Approach-to-Landing
Published in Erik Hollnagel, Handbook of Cognitive Task Design, 2003
John M. Flach, Paul F. Jacques, Darby L. Patrick, Matthijs Amelink, M. M. (Rene) Van Paassen, Max Mulder
For Langewiesche, the key to understanding a wing was the angle of attack (AOA; a). He labeled the angle of attack as the "single most important fact in the art of piloting" (p. 5). The AOA is the angle at which a wing's chord line meets the relative wind. Typically, the relative wind will be parallel and in the opposite direction to the motion of the aircraft. AOA is related to but not the same as the pitch angle or the glide path angle of the aircraft. Figure 9.1 illustrates the relations among these three angles. Aircraft are generally designed to stabilize around a specific AOA dependent on the current configuration (e.g., trim). Thus, AOA is a key to understanding how the aircraft naturally behaves so that the pilot can work with the aircraft rather than against it. Also, Langewiesche felt that AOA was critical for developing intuitions about the function of the various controls. Figure 9.1 clearly illustrates that even with longitudinal control an airplane does not typically move in the direction it is pointed as do most land vehicles. The AOA is an important factor relating the orientation (pitch; 0) and the path angle (direction of motion; y) of the aircraft. Thus, for Langewiesche, an understanding of AOA can help a pilot to see how the throttle can function as an "altitude" control and the elevator as an "airspeed" control.
Aircraft
Published in Suzanne K. Kearns, Fundamentals of International Aviation, 2021
The angle of attack is the angle at which the airflow meets the wing, between the chord line and the relative wind. When a pilot pulls back on the yoke in the cockpit, and the aircraft enters a nose-up attitude, the angle of attack of the wing increases (which increases lift and drag). With a high angle of attack, the airflow across the upper wing surface detaches from the airfoil, resulting in a loss of lift called a stall.
A computational approach to estimate the flow and output parameters of various solar updraft tower plants and a proposed model for the best power output
Published in International Journal of Sustainable Energy, 2022
Ramakrishna Balijepalli, V.P. Chandramohan, K. Kirankumar
A wind turbine blade of a SUT system was designed in the study of Ramakrishna, Chandramohan, and Kirankumar (2018). Different local climatic conditions were considered to design the blade pitch angle, relative chord length and relative wind angle. Finally, the optimized parameters were tabulated for better performance of the system. A 12.5 m2 triangular shaped collector plate was made for a SUT in Syria with a chimney diameter of 0.31 and 9 m tall (Kalash, Naimeh, and Ajib 2013). The system developed a peak velocity of 2.9 ms−1 and a peak temperature of 19 °C in winter conditions in Syria. A hybrid SUT with solar PV panels was developed in Turkey (Eryener and Kuscu 2018). They reported that the system produced 2% extra efficiency because of PV panels. 12–14 °C of temperature rise was noticed inside the chimney than the atmosphere.
Influence of Reynolds number consideration for aerodynamic characteristics of airfoil on the blade design of small horizontal axis wind turbine
Published in International Journal of Green Energy, 2022
Figure 16 shows the operational Re distribution for all the blade designs obtained by considering the local chord length of the airfoil section and local relative wind speed, as given by Eq (4). At low design tip speed ratio of 5, the blade design with fixed Re consideration of 0.5 million experience a significantly high Re distribution in the range of 0.97 to 1.48 million. Whereas, with Re consideration of 1.25 million and varying condition, the blade design experiences the Re in the range of 0.81 to 1.24 million and 0.88 to 1.24 million, respectively. With increase in the design tip speed ratio, the operational range of Re distribution for all the blade design falls to a lower range. At a design tip speed ratio of 8, the blade design with Re consideration of 0.5, 1.25, and varying condition, experiences the operational Re distribution in the range of 0.74 to 0.93 million, 0.62 to 0.78 million, and 0.70 to 0.84 million, respectively. This indicates a discrepancy in evaluating the power coefficient of the blade on account of inadequate consideration of Re for obtaining the aerodynamic characteristics of the airfoil to calculate the power coefficient.
Equivalent Static Wind Loads on Snow-accreted Overhead Wires
Published in Structural Engineering International, 2022
Hisato Matsumiya, Saki Taruishi, Mikio Shimizu, Go Sakaguchi, John H.G. Macdonald
The aerodynamic forces acting on overhead wires are usually considered to be quasi-steady forces31,32 expressed using steady-state aerodynamic coefficients. The aerodynamic forces are generated in the plane by wind speeds orthogonal to the -axis in the local coordinate system. Figure 3 shows the relationship between the wind velocity and aerodynamic force in the local coordinate system. represents the mean wind velocity vector in the plane, and represents the relative wind velocity vector. In the case of cylindrical snow accretion conditions, which are considered in snow resistance design, only drag acts on the overhead wires in the direction of the relative wind velocity. represents the increment of the angle of attack, and represents the velocity of motion of the overhead wire. The relative wind speed , increment of angle of attack, and drag can be derived via quasi-steady theory as follows: