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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.
Gas Turbine Systems Theory
Published in Tony Giampaolo, Gas Turbine Handbook: Principles and Practice, 2020
From the aerodynamic point of view there are two limiting factors to the successful operation of the compressor. They are the angle of attack of the airfoil and the speed of the airfoil relative to the approaching air (Figure 4-4). If the angle of attack is too steep, the airflow will not follow the convex surface of the airfoil. This will reduce lift and increase drag. If the angle of attack is too shallow, the airflow will separate from the concave surface of the airfoil. This also results in increased drag.
Introduction to Boundary Layer Theory and Drag Reduction
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
In a real flow field, potential flow theories of flow around an airfoil are generally applicable, which generally implies that all viscous forces may be neglected, provided the Kutta–Joukowski condition for a smooth flow at the trailing edge are imposed. The lift of an airfoil is created by a pressure differential between the bottom, or pressure side, and top, or suction side. The drag force developed is assumed to be in the same direction as the relative wind velocity direction. The net lift force is assumed to be normal to the direction of the drag force. Under such circumstances, the lift, drag and pitching moment characteristics of an airfoil can be assumed to be functions of the angle of attack alone. Given the lift force L and the drag force D per unit span and the chord length c, the coefficients of lift and drag may be defined asCscriptl=L12ρV2c,Cd=D12ρV2c.
Developing an Interactive Digital Reality Module for Simulating Physical Laboratories in Fluid Mechanics
Published in Australasian Journal of Engineering Education, 2022
Fatemeh Salehi, Javad Mohammadpour, Rouzbeh Abbassi, Shaokoon Cheng, Sammy Diasinos, Ray Eaton
Figures 8–11 present streamlines, velocity, vectors, and pressure contours around the wing which are obtained using CFD simulations. The angle of attack is defined as the angle between the chord line and the flight direction, which significantly affects the lift force. As can be seen, at the angle of attack of zero, the streamlines are smooth around the wing. However, increasing the angle of attack to 15º results in separation and vortex shedding on the wing and downstream. The CFD data is consistent with the observation in the wind tunnel; however, it is able to provide much more detail on the flow variations, such as pressure and velocity fields. A closer look at Figure 11 reveals that a larger attack angle leads to lower pressure on the top side and higher pressure at the bottom of the wing, which enhances the lift. Students use VR headsets to virtually walk around the object, helping them to better understand the key flow features. As a part of the assessment task, they require to discuss how the change in the angle of attack affects the velocity and pressure fields. The visualisation of streamlines helps them to better understand the flow separation in external flows. The ability to visualise pressure and velocity fields is another key advantage of the VR module, which is not feasible in physical wind tunnel laboratories. This is consistent with the reported benefits of VR in education: it enables the elaboration and realisation of details and pushes the boundaries of reality (Slater and Sanchez-Vives 2016).
Synthetic jet application in the wind turbine concentrator design
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Teoman Oktay Kutluca, Emre Koç, Tahir Yavuz
As the angle of attack increases, the ability of the flow to adhere to the upper surface of the airfoil decreases and the separation occurs after an angle of attack. For this reason, the increase in the angle of attack in the flow on the airfoil linearly increases the lift coefficient up to a certain value, and then the lift coefficient starts to decrease after the critical value at the stall angle. The reason for this situation is that the flow on the upper surface of the airfoil breaks off in the areas very close to the leading edge from the standpoint of the stall and reverse flow is observed in a large part of the upper surface.
An optimized airfoil geometry for vertical-axis wind turbine applications
Published in International Journal of Green Energy, 2020
A. Meana-Fernández, L. Díaz-Artos, J.M. Fernández Oro, S. Velarde-Suárez
Figure 16 shows the normalized pressure contours around the airfoil at the different angles of attack studied. It may be appreciated how, with the increase in the angle of attack, the pressure on the pressure side of the airfoil increases and the pressure on the suction side decreases. For negative angles, the pressure and suction sides interchange. A stagnation point is observed, which moves toward the leading edge with the increase in the angle of attack.