Contrasting flow dynamics between stationary and moving clapping bodies

Mahulkar, SV and Arakeri, JH (2024) Contrasting flow dynamics between stationary and moving clapping bodies. In: Physical Review Fluids, 9 (11).

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Abstract

In bioinspired pulse jet studies, the apparatus is typically stationary. But does this truly reflect natural flow dynamics where an animal is in motion We examine this experimentally using a clapping body and report differences in flow dynamics and body kinematics between the body that is allowed to propel forward freely (dynamic) and one that is constrained from moving forward (stationary). The experiments were done in quiescent water. The body consists of two interconnected plates hinged at one end with a "torsion"spring. Initially, a thread loop holds the plates apart at an interplate angle of 60�. Cutting of the thread initiates the clapping motion, and if allowed, the body propels forward a certain distance. Experiments have been performed for three values of d�(=depth/length): 1.5, 1.0, and 0.5. In both cases, vortex loops initially develop along the three edges of each plate, which reconnect by the end of the clapping motion resulting in the formation of an elliptical vortex loop in the wake for d�=1.5, 1.0 bodies, and multiple connected rings for d�=0.5 bodies. Three main and unexpected differences are observed between the "dynamic"and "stationary"bodies. In the dynamic case, the clapping action is faster compared to the stationary case, with the maximum angular plate velocity being twice as high. The mean thrust coefficient, CT¯, based on plate tip velocity, is higher for the stationary case. The value of CT¯ and the circulation in the starting vortices is almost independent of d� for the dynamic case, whereas it increases with d� for the stationary case. Control volume analysis showed that significant lateral flow in stationary cases leads to depth-dependent variations in circulation and thrust coefficient, while negligible sideways flow in the dynamic cases eliminates these variations. © 2024 American Physical Society.

Item Type:	Journal Article
Publication:	Physical Review Fluids
Publisher:	American Physical Society
Additional Information:	The copyright for this article belongs to publisher.
Keywords:	Kinematics; Metabolism; Radial flow; Wakes, Body kinematics; Elliptical vortex; Flow body; Flow dynamics; Natural flow; Plate velocity; Pulse jet; Thrust coefficients; Torsion Springs; Vortex loops, Vortex flow
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	17 Dec 2024 05:57
Last Modified:	17 Dec 2024 05:57
URI:	http://eprints.iisc.ac.in/id/eprint/87130

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