2010
DOI: 10.1017/s0022112010000583
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Hovering of a rigid pyramid in an oscillatory airflow

Abstract: We investigate the dynamics of rigid bodies (hollow 'pyramids') placed within a background airflow, oscillating with zero mean. The asymmetry of the body introduces a net upward force. We find that when the amplitude of the airflow is above a threshold, the net lift exceeds the weight and the object starts to hover. Our results show that the objects hover at far smaller air amplitudes than would be required by a quasi-steady theory, although this theory accounts qualitatively for the behaviour of the system as… Show more

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Cited by 17 publications
(62 citation statements)
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“…We think that our numerical results are helpful to better understanding of the experimental results and the hovering mechanism for an asymmetric body. For example, Weathers et al (2010) observed that the lift force was higher than that predicted from the quasi-steady theory, and simply attributed the reason to the acceleration effect; here we observe that the vortex effect is very important and can be more important than the added mass effect when the Reynolds number is relatively high. Liu et al (2012) conjectured that the sideway jet was responsible for the stable hovering, and our results confirmed this conjecture for the unstable regime, but for the stable regime, we provide a new explanation with the shifts in the positions of the flow stagnation point on the body edge and the projection point of the body mass center on the edge.…”
Section: Introductionsupporting
confidence: 39%
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“…We think that our numerical results are helpful to better understanding of the experimental results and the hovering mechanism for an asymmetric body. For example, Weathers et al (2010) observed that the lift force was higher than that predicted from the quasi-steady theory, and simply attributed the reason to the acceleration effect; here we observe that the vortex effect is very important and can be more important than the added mass effect when the Reynolds number is relatively high. Liu et al (2012) conjectured that the sideway jet was responsible for the stable hovering, and our results confirmed this conjecture for the unstable regime, but for the stable regime, we provide a new explanation with the shifts in the positions of the flow stagnation point on the body edge and the projection point of the body mass center on the edge.…”
Section: Introductionsupporting
confidence: 39%
“…Spagnolie & Shelley (2009) numerically studied the flow structures and dynamics of an actively shape-changing body subject to an oscillatory flow and demonstrated that the body could hover or ascend by shuttling momentum-carrying vortex dipoles downward into the fluid. Weathers et al (2010) observed that a rigid pyramid was able to hover stably in an oscillatory air flow at far smaller air amplitudes than would be required by a quasi-steady theory. Liu et al (2012) investigated the stability of flapping flight in a model system that consists of a pyramid-shaped object hovering in a vertically oscillating airflow, and argued that the vortices shed from the body produced the restoring torque for stable hovering.…”
Section: Introductionmentioning
confidence: 96%
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“…Experimental examples of NeVRs are generated by time-dependent kinematics of physical bodies (Dabiri et al 2005;Weathers et al 2010;Liu et al 2012). The circulation of NeVRs created in this way can be controlled by setting the flow parameters (Weathers et al 2010;Liu et al 2012), but the overall configuration is fixed by the experimental set-up.…”
mentioning
confidence: 99%
“…The circulation of NeVRs created in this way can be controlled by setting the flow parameters (Weathers et al 2010;Liu et al 2012), but the overall configuration is fixed by the experimental set-up. In contrast to this, numerical simulations can use artificial set-ups to gain deeper insight into vortex dynamics (Pradeep & Hussain 2004;Bergdorf, Koumoutsakos & Leonard 2007;O'Farrell & Dabiri 2012).…”
mentioning
confidence: 99%