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Structure and entrainment in the plane of symmetry of a turbulent spot

Cantwell, Brian and Coles, Donald and Dimotakis, Paul (1978) Structure and entrainment in the plane of symmetry of a turbulent spot. Journal of Fluid Mechanics, 87 (4). pp. 641-672. ISSN 0022-1120. https://resolver.caltech.edu/CaltechAUTHORS:20120725-101139034

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Abstract

Laser-Doppler velocity measurements in water are reported for the flow in the plane of symmetry of a turbulent spot. The unsteady mean flow, defined as an ensemble average, is fitted to a conical growth law by using data at three streamwise stations to determine the virtual origin in x and t. The two-dimensional unsteady stream function is expressed as ψ=U^2_∞tg(ξ,η) in conical similarity co-ordinates ζ = x/U_∞t and η = y/U_∞t. In these co-ordinates, the equations for the unsteady particle displacements reduce to an autonomous system. This system is integrated graphically to obtain particle trajectories in invariant form. Strong entrainment is found to occur along the outer part of the rear interface and also in front of the spot near the wall. The outer part of the forward interface is passive. In terms of particle trajectories in conical co-ordinates, the main vortex in the spot appears as a stable focus with celerity 0·77U_∞. A second stable focus with celerity 0·64U_∞ also appears near the wall at the rear of the spot. Some results obtained by flow visualization with a dense, nearly opaque suspension of aluminium flakes are also reported. Photographs of the sublayer flow viewed through a glass wall show the expected longitudinal streaks. These are tentatively interpreted as longitudinal vortices caused by an instability of Taylor-Görtler type in the sublayer.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1017/S0022112078001809 DOIUNSPECIFIED
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=380120&fulltextType=RA&fileId=S0022112078001809PublisherUNSPECIFIED
Additional Information:© 1978 Cambridge University Press. Received 31 May 1977 and in revised form 3 October 1977. Published Online April 12 2006. This research was supported by the National Science Foundation under grant ENG75-03694.
Group:GALCIT
Funders:
Funding AgencyGrant Number
NSFENG75-03694
Issue or Number:4
Record Number:CaltechAUTHORS:20120725-101139034
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20120725-101139034
Official Citation: Brian Cantwell, Donald Coles and Paul Dimotakis (1978). Structure and entrainment in the plane of symmetry of a turbulent spot. Journal of Fluid Mechanics, 87 , pp 641-672 doi:10.1017/S0022112078001809
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32709
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:25 Jul 2012 17:26
Last Modified:03 Oct 2019 04:03

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