By Wei Shyy, Yongsheng Lian, Jian Tang, Dragos Viieru, Hao Liu
Low Reynolds quantity aerodynamics is critical to a couple of normal and man-made flyers. Birds, bats, and bugs were of curiosity to biologists for years, and lively learn within the aerospace engineering neighborhood, prompted by means of curiosity in micro air automobiles (MAVs), has been expanding speedily. the first concentration of this booklet is the aerodynamics linked to mounted and flapping wings. The ebook reflect on either organic flyers and MAVs, together with a precis of the scaling laws-which relate the aerodynamics and flight features to a flyer's sizing at the foundation of easy geometric and dynamics analyses, structural flexibility, laminar-turbulent transition, airfoil shapes, and unsteady flapping wing aerodynamics. The interaction among flapping kinematics and key dimensionless parameters resembling the Reynolds quantity, Strouhal quantity, and diminished frequency is highlighted. some of the unsteady raise enhancement mechanisms also are addressed, together with modern vortex, swift pitch-up and rotational movement, wake seize, and clap-and-fling.
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Additional info for Aerodynamics of Low Reynolds Number Flyers
Based on the insight into the flapping frequency, it is possible to estimate the power output from a bird’s flight muscles and achieve an estimation of the power required for flying. According to Pennycuick (1975) it is possible to estimate the maximum flapping frequency fw,max for geometrically similar animals, as shown in the following discussion. Because the force Fm exerted by a muscle is assumed to be proportional to the cross-sectional area of its attachment, we get Fm ∼ S ∼ l 2 . 10) Pennycuick (1975) assumes that the stresses in muscles and bones are constant and that the torque acting about the center of rotation of the proximal end of the limb, with length l, can be expressed as JT = Fml.
For fast forward flight the downwash velocity is small and can be largely neglected. With a larger wing span, Uf increases and changes its direction, which affects the magnitude and direction of Ur . 14. Velocity-force vector diagram at different flapping wingspan locations for fast forward flight. Here, the lift and drag are defined based on the effective velocity combining forward and local flapping velocities. , in the vertical direction, and drag/thrust in the horizontal direction. According to the resulting force vector F illustrated here, drag of the vehicle is generated by the inner wing, and thrust of the vehicle is generated by the outer wing.
The trailing vortices (the tip vortices) are of the same circulation magnitude as the bound vortex. At the beginning/end of the downstroke, when the flapping velocity changes direction, a transverse vortex (starting/stopping vortex) is produced at the trailing edge, and, according to Kelvin’s circulation theorem, these two transverse vortices connect the two tip vortices and result in the shedding of a vortex ring. Some flyers (for example, doves) make use of the clap-and-fling mechanism to generate the starting vortex and reduce the delay in building up maximum lift during the first part of the downstroke.