The objective of this study is to visualize the chaotic mixing patterns induced by oscillatory flow in a curved tube. The velocity field during oscillatory flow in a curved tube with inner diameter of 10 mm and tube length of 314 mm was numerically simulated using the commercial software Fluent. The working fluid was water and the flow was assumed to be three-dimensional, laminar, unsteady, and incompressible. To clarify the effect of the curvature, the ratio of the tube radius to the curvature radius a/b was varied from 0.0125 to 0.075, and oscillatory flow frequency f was varied from 0.5 to 2.0 Hz. To visualize the fluid mixing patterns, trajectories were also calculated for the minute particles that follow convective movement. To examine the chaotic features of flow, the largest Lyapunov exponent was then evaluated. The visualized flow patterns revealed the characteristic fluid mixing patterns with stretching and folding of fluid in the radial and longitudinal cross-sections, and line length drawn by particles increased with increasing a/b and with decreasing f. The average value of the largest Lyapunov exponent was positive under all flow conditions and was changed in response to the line length. These results indicate that the flow mixing pattern induced by oscillatory flow in a curved tube is chaotic.

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Recently, various studies of Micro Air Vehicle (MAV) and Unmanned Air Vehicle (UAV) have been reported from wide range points of view. The aim of this study is to research the aerodynamic improvement of a flapping wing in low Reynold’s number region to develop an applicative these air vehicle. The six kinds of elliptical wings made of stainless steel are used in the flapping wing. The effects of flapping amplitude and wing configuration regarding the aerodynamic characteristics are investigated in detail. The fluid force measurement by six component load cell and PIV analysis are performed as the experimental method. In the flapping wing experiment, the simultaneous measuring of the fluid force measurement and PIV analysis is tried by using the trigger signal from the encoder attached to the flapping model. The relations between the aerodynamic superiority and the vortex behavior around the models are demonstrated.

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