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Wind turbine electricity generation for desalination: design, application and commercialization
Published in Hacene Mahmoudi, Noreddine Ghaffour, Mattheus Goosen, Jochen Bundschuh, Renewable Energy Technologies for Water Desalination, 2017
Zhao Yong, Zheng Shuai, Chua Leok Poh
For the aerofoils S822 and S823, the drag coefficient, Cd, increases more slowly than the lift coefficient, Cl, from the point of minimum Cl/Cd ratio to the point where Cl reaches a maximum value. According to Burton et al. (2011), the drag effect due to skin friction can be ignored as long as the flow remains attached to the blade because the losses caused by drag are only critical when the wind turbine is operating at a high tip speed ratio. The variation of maximum power coefficient versus tip speed ratio is shown in Figure 8.9a. The wind turbine power coefficient, Cp, is the ratio of the power generated by a wind turbine to the total wind power. Since the lift-to-drag ratios and design tip speed ratio for both S822 and S823 are relatively low, the angle of attack will be selected near the point where Cl achieves its maximum value.
UAS Airframe and Powerplant Design
Published in Douglas M. Marshall, R. Kurt Barnhart, Eric Shappee, Michael Most, Introduction to Unmanned Aircraft Systems, 2016
The remaining sources of parasite drag, to some extent, all affect the performance (e.g., range, endurance, useful load, required thrust) of a UAS. Skin friction drag develops from the shearing stresses that dissipate energy in the thin boundary layer above the surfaces of the aircraft. Leakage drag, which is generally associated with fixed-wing aircraft and accounts for 1%–2% of total drag (Sadraey 2009), results from the change in momentum of the air flowing through the gaps between fixed and moveable surfaces (e.g., ailerons, flying wing flaperons, elevators, rudders, flaps, ruddervators). Based on the frontal area presented to the airstream, form drag (aka, pressure drag or flat plate drag) results from the unbalanced pressure distributions across the area of the projected shape presented to the viscous flow and the turbulence it creates. Thrust must overcome this pressure differential in order to move the aircraft forward. Interference drag results from the energy losses resulting from the interaction of airflows at the juncture of various components. Where stabilizers join empennage and wings mate to the fuselage, the flows converge and interact to produce turbulence, shearing, and separation of the boundary layers—all of which are wasteful of energy—creating interference drag. The existence of interference drag explains why total drag is actually greater than the sum of all the drag acting on all components of the aircraft. Finally, cooling drag results from the loss of momentum and total pressure in the air flowing over the powerplant to carry away heat (Sadraey 2009).
ASCE 7-16 for Flood Loads
Published in Syed Mehdi Ashraf, Structural Building Design: Wind and Flood Loads, 2018
Drag coefficient is a dimensionless quantity used to assess the resistance of an object in a fluid environment. A low value of drag coefficient implies that the structural element will have less resistance to the flow of water. Drag coefficient depends on the shape of the structural element. The two contributors to drag coefficient are skin friction and form drag. Skin friction arises from the friction of the fluid against the “skin” of the structural element around which the fluid is moving. Form drag arises from the shape of the object. The general size and shape of the body are the most important factors in form drag. Bodies with a larger cross-section will have a higher drag. Smoother bodies will have lower drag coefficients. Values of drag coefficient of some common shapes are provided in Table 8.1 of the book. The Coastal Construction Manual provides values of drag coefficient for other shapes based on the parameters shown in Table 8.2 of the book. The value of drag coefficient shall be taken as at least 1.25 in the calculations of forces on structural elements. The drag coefficient is determined by using one of the following ratios: The ratio of the width of the object (w) to the height of the object (h) if the object is completely immersed in waterThe ratio of the width of the object (w) to the still-water flood depth of the water (dh) if the object is not fully immersed
Free convective couette flow analysis of viscoelastic dusty fluid along with Newtonian heating in a rotating frame
Published in Waves in Random and Complex Media, 2022
Dolat Khan, Gohar Ali, Poom Kumam, Ata ur Rahman, Wiboonsak Watthayu, Ahmed M. Galal
Drag force is the force that reduces the motion of the fluid. Skin friction is one of the drag force which occurs between the surface and fluid. In this particular problem at the skin fraction is formed by the fraction between the fluids across the surface of the lower plate. In the case of viscoelastic non-Newtonian fluid, the equation for the skin friction is: Using Equation (17) in Equation (33), we obtained the below equation for skin fraction in dimensionless form:
Large eddy simulations of the turbulent channel flow over dimpled surfaces
Published in Journal of Turbulence, 2023
Yasin Kaan İlter, Aras Çetinkaya, Uğur Oral Ünal
Skin friction is the main component of the overall drag force for most fluid flows. Both restrictive legislation as a result of environmental measures and economic reasons have made the energy efficiency issue very important [1]. Reducing skin friction has a key role in the efficiency of rail, highway and airway transport vehicles or naval systems such as ships and underwater vehicles.