14:00
Computational Fluid Dynamics II
Chair: Ido Akkerman
14:00
30 mins
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FLUID DYNAMICS OF A SELF-PROPELLED FLAPPING PECTORAL FIN BY FLUID-MOTION COUPLING IMMERSED BOUNDARY METHOD
Ningyu Li, Yumin Su, Weixing Liu
Abstract: Dynamical behaviors of a self-propelled flapping pectoral fin are investigated by developed immersed boundary (IB) method, in which a robust numerical strategy is proposed to deal with complex moving boundaries involved in biomimetic flow simulations and the fluid-motion coupling is embodied. The fin is modeled as a pectoral-fin-shaped flapping plate with a freedom in the horizontal direction. We have investigated the unsteady process of the fin locomotion and corresponding mechanisms in detail and compared the complex-shaped low-aspect-ratio fin with symmetric foils. A parametric study is also carried out to discuss the effect of key governing parameters. The results show that the fin can reach the fully developed state earlier and induce faster lateral velocity with increasing flapping frequency or flapping amplitude. Moreover, the linear relationship between translational Reynolds number and frequency Reynolds number is found as the latter is over a critical value. As the flapping amplitude is raised, the translational Reynolds number rapidly increases in an approximately linear way, and thereafter a relatively slow growing trend is observed.
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14:30
30 mins
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RESEARCH ON SUPPRESSION OF CAVITY FLOW INDUCED NOISE BY FLOW CONTROL METHOD
Wang Xing, Zhang Nan, Xie Hua, Wu Baoshan
Abstract: The suppression of non cavitating flow induced noise over a cavity is an important and complex issue in fluid-dynamic acoustics field. In hydroacoustics, it is short of an intensive investigation for the problem．So a flow control method (airfoil guide vanes) was analyzed with the numerical simulation and model test to reduce the noise of the cavity in this paper. The flow past the cavity is simulated numerically by large eddy simulation with three different meshes to analyze the grid convergence. The structures of the vortical flow are captured by Vortex identification (Q) and the spectrum of the cavity vertical oscillation velocities in ten different positions are shown. Then the flow fields past the cavity with airfoil guide vanes of different heights and number are simulated numerically. After that, the flow induced noise of different models is computed by Powell vortex sound equation. Finally, the flow induced noise of the cavity with five NACA0010 airfoil guide vanes of 0.02m height is measured in the Cavitation Tunnel of CSSRC. Through the experimental measurement of the flow induced noise, it is found that with the airfoil guide vanes, the effective suppression to flow induced noise is obtained.
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