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Replaces tangential blowing with alternating tangential blowing/suction in boundary layer control. Implication of boundary-layer separation; Numerical simulations based on Navier-Stokes equations; Variation of the aerodynamic forces.

The effects of stroke deviation of a flapping model insect wing on its aerodynamic force production are studied by solving the Navier-Stokes equations. Stroke deviation of a flapping wing often takes the forms of various out-of-plane wing-tip trajectories that depend on the time variation of the stroke deviation angle. In the present paper, four typical wing-tip trajectories, referred to as cases A-D, were used to investigate the effect of stroke deviation by comparing the aerodynamic forces, flows, and power requirements of the flapping wings with and without stroke deviation. The stroke deviation has remarkable influences on the time course of the aerodynamic force of a flapping wing. The influences could be explained by two mechanisms: one is the added-rotation effect, which is introduced by the deviation angle of the wing; the other is the change in effective angle of attack of the wing, which is due to the angular speed of the deviation. In general, the stroke deviation only produces a small effect on the cycle-mean aerodynamic forces, because the changes due to stroke deviation could be roughly offset in a wingbeat cycle. The analysis of power requirements shows that stroke deviation will generally lead to an increase in energy consumption for insect flights, indicating that insects should have the tendency to maintain the flapping motion in a plane for hovering or low-speed flight, as is observed in nature. [ABSTRACT FROM AUTHOR]

The article presents the study "Dragonfly Forewing -- Hindwing Interaction at Various Flight Speeds and Wing Phasing," conducted by Hua Huang and Mao Sun of Beijing University of Aeronautics and Astronautics in China. Scientists have always been enthralled by dragonflies' flight. Researchers are starting to study dragonfly areodynamics and the forewing-hindwing interactions using three-dimensional model wings due to the advances in computational and experimental techniques and facilities.

Aerodynamic force generation in hovering flight in a tiny insect, Encarsia formosa, has been studied. The Reynolds number of the flapping wings (based on the mean chord length and the mean flapping velocity) is around 15. The flapping motion of the insect is unique in that the wing pair "claps" together near the end of an upstroke and "flings" open at the beginning of the subsequent downstroke. The method of solving the Navier-Stokes equations over moving overset grids is used. The fling produces a large lift peak at the beginning of the downstroke, the mechanism of which is the generation of a vortex ring containing a downward jet in a short period; the clap produces a large lift peak near the end of the subsequent upstroke by a similar mechanism. Because the vorticity generated during the clap and fling diffuses rapidly, the clap and fling has little influence on the flows in the rest part of the stroke cycle. The mean lift is enough to support the weight of the insect. The lift peaks due to the clap and fling result in more than 30% increase in mean lift coefficient compared to the case of flapping without clap and fling. [ABSTRACT FROM AUTHOR]