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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.
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Bodies immersed in flowing fluids experience forces due to the shear stresses and pressure differences caused by the fluid motion. Drag is the force parallel to the flow direction and lift is the force perpendicular to the flow direction. Streamlining is the art of shaping a body to reduce the fluid dynamic drag force. Airfoils (and hydrofoils) are designed to produce lift in air (or water); they are streamlined to reduce drag and attain high lift/drag ratios.
Introduction to Aerodynamics
Published in Thomas Corke, Robert Nelson, Wind Energy Design, 2018
As discussed earlier, airfoils are generally classified as having symmetrical or cambered section shapes. For a symmetrical airfoil, the lift coefficient is zero when the angle of attack is zero. The aerodynamic lift increases linearly with increasing angle of attack until at higher angles of attack, the air flow over the airfoil can no longer follow the curvature of the airfoil upper (suction) surface and the flow “separates”. If the flow separation begins at the trailing edge and moves forward with increasing angle of attack, the rate of increase in the lift coefficient diminishes and then begins to decrease. This is illustrated in the lift coefficient versus angle of attack for a symmetric airfoil shown in Figure 3.4. The angle of attack where the lift coefficient reaches its maximum is referred to as the stall angle of attack, αs. The stall exhibited in Figure 3.4would be considered to be “very gentle”. This is typical of a “thicker” airfoil section shape. The airfoil thickness is generally categorized by the ratio of its maximum thickness to its chord length, namely t/c. For “thin” airfoil sections, the air flow over the suction surface of the airfoil may separate abruptly from the leading edge, with a sharp drop in the lift coefficient. An example of this behavior is presented later in this chapter.
Aerodynamic Efficiency and Performance Development in an Electric Powered Fixed Wing Unmanned Aerial Vehicle
Published in Electric Power Components and Systems, 2023
Berk Kaynak, Ahmet Yigit Arabul
In the simulation phase, variations on increasing the lift force of the aircraft wings are determined and CFD analyzes are performed. The profile that surrounds the outer side of the wing in the side view is called the wing profile. In the most basic terms, an airfoil is the cross-sectional shape of a wing. The CL provided by each airfoil is different. This value changes according to the angle made by the leading edge of the wing with the incoming air flow. This angle is called the angle of attack. This critical angle is called the stall angle [31]. The wing of the aircraft has a 4° incidence angle. Power consumption will be reduced owing to the angle of attack to be provided by the flight controller in order to decrease the cruise flight speed. One of the ways to decrease the flight speed of the aircraft is an increase in wing area [24].
Development of an analytical model for the flexural vibration of fish bone active camber structures with truncated, variable thickness partitions
Published in Mechanics Based Design of Structures and Machines, 2022
Mahdi Nejati, Saeed Shokrollahi, Masoud Cheraghi
After establishing the validity of the developed formulation for partitioned plates of different heights that might also have variable thickness and be truncated along their edges, it is now time to consider a few cases for real scenarios where FishBAC is implemented. It was stated earlier that FishBAC can be built around different airfoils, which may or may not have a slope on their camber line in the trailing edge section. Accordingly, this article considers two different types of airfoils, i.e., a symmetric NACA 4-series airfoil and a cambered 5-digit NACA airfoil in different configurations. The results are then compared with the findings of COMSOL Multiphysics for different mode numbers.
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.