What are the factors that affect the efficiency of flapping foils?4 answersThe efficiency of flapping foils is affected by several factors. One factor is the shape of the foil, specifically the thickness of the foil between the 18th and 50th percent along the chord, with thicker leading-edges and sharper trailing-edges resulting in higher efficiency. Another factor is the aspect ratio (AR) of the foil, with increasing slenderness improving thrust coefficients and thrust augmentation, although the benefits level off at higher values of AR. The configuration of multiple flapping foils also plays a role, with the tandem configuration being optimal for multiple foils in terms of energy harvesting efficiency, but also expanding the diffusion range of wake turbulence. Additionally, the phase difference and vertical spacing between multiple foils affect energy harvesting performance, with the stepwise configuration maximizing the utilization of vertical spacing and achieving higher efficiency. Finally, the dimensionless heaving amplitude, pitching amplitude, and flapping frequency of a single flapping wing also impact energy extraction efficiency.
Twist angle effect on stability of flying wing proformance?4 answersThe effect of twist angle on the stability and performance of flying wings has been studied in several papers. It has been found that increasing the twist angle can improve aerodynamic efficiency over a wide range of angles of attack, but at 0° angle of attack, the efficiency may decrease significantly. The twist angle also affects the pitching moment and lift-to-drag ratio. Negative twist delays the onset of pitch-break at higher angles of attack, while positive twist can lower the angle of attack at which pitch-break occurs and increase the lift-to-drag ratio. The spanwise distribution of twist angle is also important, with quadratic profiles performing better for moderate to high wingspans and linear profiles performing better for smaller wingspans. Overall, wing twist plays a crucial role in the stability and performance of flying wings, affecting efficiency, aerodynamic forces, and the onset of pitch-break.
What are the factors that influence the angle of draw?5 answersThe factors that influence the angle of draw include the overburden stiffness and the extraction seam dip angle. Additionally, the child's understanding of angle is influenced by various factors such as the perspective used (static or dynamic), the representational system (oral, written, or body-syntonic), the situation (rotation, navigation, or comparison), the materials used, the required action by the child, and the size of the angle. Drawing accuracy of angles is also influenced by perceptual encoding, as shown by the misperception hypothesis of drawing errors. Furthermore, the binder angle significantly influences the draw bead pulling force, with different materials and bead geometries resulting in varying pulling forces at different binder angles. The haptic perception of raised-line drawings is influenced by the exploration strategy, local apex information, and global angular extent.
What are the different types of flapping wing mechanisms used in UAVs?5 answersFlapping wing mechanisms used in UAVs include the incorporation of flight characteristics of birds and bats, the use of flapping actuators to induce flapping motion, and the utilization of variable-inclination-angle swinging wings. These mechanisms are critical in determining the aerodynamic performance of the UAVs and contribute to their maneuverability, inconspicuousness, and flight efficiency in low Reynolds number regions. Additionally, there is a need for UAVs with adjustable dihedral angles to optimize roll stability and maneuverability based on flight conditions. The use of root spars and attitude control actuators allows for changes in the angle of attack of the wings, introducing pitching moments to the flapping wing micro aerial vehicles. These different types of flapping wing mechanisms provide flexibility and control in UAV flight.
How can angle of attack effect drag coefficient in wind turbine blades?2 answersThe angle of attack of incoming flow velocity has an effect on the drag coefficient of wind turbine blades. The maximum icing thickness on the blade surface is positively correlated with the water collection efficiency, and the larger absolute value of the angle of attack, the larger the icing area on the blade surface. The impact of varying pitch angles on the performance parameters of a horizontal axis wind turbine shows that the power generated by the turbine is maximum for its corresponding optimum pitch angle. State of the art 3D CFD codes are capable of predicting the correct dependency of the integrated drag of a flat plate placed perpendicular to the flow, and the computed drag distribution along the plate span deviates from the general expectation of 2D behavior at the central part of the plate. The optimum design attack angle for fixed-pitch variable-speed wind turbine blade design is determined based on the aerodynamic characteristics, such as lift and drag coefficients and lift to drag ratio. The variation of local angle of attack influences the lift coefficient and causes a large change in the lift of wind turbine blades.
Why there is a difference in lift and drag values while using different angles of attack?3 answersThe difference in lift and drag values while using different angles of attack is due to various factors. The abstracts provide insights into these factors. According to Spalart, at zero angle of attack, the lift and drag coefficients vanish proportionally to the diameter-to-length ratio of the body. Bhattacharyya et al. conducted numerical analysis on an airfoil and found that the coefficient of drag and lift varied at different angles of attack. Zhang et al. developed a method to determine the optimal sliding angle of an underwater glider, which affects the lift and drag forces at different attack angles. Park et al. conducted a parametric study on elliptic cylinders and observed that the angle of attack significantly affects the lift and drag forces. Therefore, the difference in lift and drag values while using different angles of attack can be attributed to factors such as the shape of the body, the angle of attack, and the Reynolds number.