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Experimental investigation of stationary and rotational structures in non-circular hydraulic jumps

Published online by Cambridge University Press:  03 December 2014

A. R. Teymourtash  and
M. Mokhlesi
A. R. Teymourtash*
Affiliation:
Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, 91775-1111, Iran
M. Mokhlesi
Affiliation:
Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, 91775-1111, Iran
*
†Email address for correspondence: [email protected]
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Abstract

When a vertical liquid jet impacts on a solid horizontal surface, the first expectation is to have a circular hydraulic jump. However, in some conditions, for highly viscous fluids, the transition from supercritical to subcritical flow occurs with non-circular shapes such as polygons. Indeed, a quick rotational wave appears on the circular jump before the formation of a polygonal form, which may be related to the Rayleigh–Plateau instability. In this paper, stable polygonal jumps are studied to complete this research. The region of stability is defined for polygonal jumps, and the dependence of this region on the flow governing dimensionless groups is determined experimentally. The results confirm the multistability (hysteresis) of the polygonal jumps, and imply that polygonal jumps with different corner numbers can be created in a certain parameter regime. The size and curvature of the sides of the polygons due to variations of flow rate and downstream obstacle height are also investigated. In addition to the stable ones, our experiments reveal a new type of polygonal jump that has an unstable structure and displays a rotational behaviour with a constant angular velocity, which we call it, ‘rotational hydraulic jump’. It is observed that the angular velocity of this kind of jump depends on the jet flow rate, jet radius and downstream height of the jump. Our observations suggest that the nature of the rotational jump is some kind of surface wave along the jump in clockwise or anticlockwise direction. It seems that the rotational jump has a flow structure that is the same as a type IIb jump. The jump dimensions are studied; the inscribed and circumscribed circular radii of each polygon are measured in order to compare the various polygons together and to find a mean jump radius to compare with Watson’s theory.

JFM classification

Waves/Free-surface Flows: Hydraulics Instability: Instability Waves/Free-surface Flows: Waves/Free-surface Flows
Type
Papers
Information
Journal of Fluid Mechanics , Volume 762 , 10 January 2015 , pp. 344 - 360
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Copyright
© 2014 Cambridge University Press 

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References

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Teymourtash and Mokhlesi supplementary movie

A new type of non-circular hydraulic jumps is observed in this study with a rotational- wavelike behavior with a constant angular velocity that we call it rotational hydraulic jump. The end of nozzle is marked by a white band.

Download Teymourtash and Mokhlesi supplementary movie(Video)
Video 5.7 MB

Teymourtash and Mokhlesi supplementary movie

A rotational hydraulic jump due to impingement of a vertical jet onto a solid and horizontal glass plate; viewed from directly below through the impact glass target plate. The working liquid is ethylene glycol with density ρ=1.1kg/m3, viscosity ν=11.8cS and surface tension of σ=47.5dyn/cm.

Download Teymourtash and Mokhlesi supplementary movie(Video)
Video 5 MB

Teymourtash and Mokhlesi supplementary movie

Injection of dye and air microbubbles in the liquid in order to visualize the structure of a rotational hydraulic jump; it seems that the nature of this phenomenon is some kind of surface waves along the jump and there are some eddies close to edges of the polygonal jump towards the corners.

Download Teymourtash and Mokhlesi supplementary movie(Video)
Video 18 MB