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Experimental studies of a distorted turbulent spot in a three-dimensional flow

Published online by Cambridge University Press:  26 April 2006

M. Jahanmiri
Affiliation:
Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560 012, India Present address: Department of Mechanical and Aerospace Engineering, University of Science and Technology, Shahin Shahr City, Ishfahan, Iran.
A. Prabhu
Affiliation:
Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560 012, India
R. Narasimha
Affiliation:
Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560 012, India The Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India

Abstract

We report here on the results of a series of experiments carried out on a turbulent spot in a distorted duct to study the effects of a divergence with straight streamlines preceded by a short stretch of transverse streamline curvature, both in the absence of any pressure gradient. It is found that the distortion produces substantial asymmetry in the spot: the angles at which the spot cuts across the local streamlines are altered dramatically (in contradiction of a hypothesis commonly made in transition zone modelling), and the Tollmien–Schlichting waves that accompany the wing tips of the spot are much stronger on the outside of the bend than on the inside. However there is no strong effect on the internal structure of the spot and the eddies therein, or on such propagation characteristics as overall spread rate and the celerities of the leading and trailing edges. Both lateral streamline curvature and non-homogeneity of the laminar boundary layer into which the spot propagates are shown to be strong factors responsible for the observed asymmetry. It is concluded that these factors produce chiefly a geometric distortion of the coherent structure in the spot, but do not otherwise affect its dynamics in any significant way.

Type
Research Article
Copyright
© 1996 Cambridge University Press

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