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4th Thermal and Fluids Engineering Conference

ISSN: 2379-1748

UNSTEADY WAKE CHARACTERISTICS IN FLOW PAST TWO INLINE SURFACE MOUNTED CIRCULAR CYLINDERS

Prashant Kumar
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, 600036, India

Shaligram Tiwari
Department of Mechanical Engineering, Indian Institute of Technology Madras Chennai, India, 600036

DOI: 10.1615/TFEC2019.cmd.028455
pages 437-450


KEY WORDS: Inline finite height circular cylinders, modes of vortex shedding, horseshoe vortex, Hilbert spectra, marginal spectra, lift and drag.

Abstract

Three-dimensional numerical investigations have been carried out for flow past inline finite height circular cylinders of different heights mounted on a plate surface. Aspect ratio (AR = ratio of height to diameter of cylinder) of downstream cylinder is fixed equal to 5 whereas for upstream cylinder it varies from 1 to 5. Flow Reynolds number is fixed and is equal to 300. Effects of size of upstream cylinder and inter-cylinder spacing (S) on wake characteristics behind both the cylinders have been examined using instantaneous vorticity contours and iso Q-surfaces. Three different shedding modes have been observed with change in S, viz. single slender mode, reattachment mode and binary or co-shedding mode. Formation of various vortical structures in different zones, such as horseshoe vortex in front of the upstream cylinder, hairpin vortical structures and long streamwise slender structures in the downstream wake have been discussed. It is observed that vortex shedding behavior changes along the height of the cylinder in the upstream wake from steady flow near free end to unsteady vortex shedding near plate surface. Vortex shedding frequency behind the downstream cylinder is found to vary with change in AR. Unsteady wake behavior has been analyzed using Hilbert spectral analysis of time varying signals. Evolution of nonlinearity in the wake with changes in S and AR has been studied with the help of marginal spectra. Dynamic forces (lift and drag) on each cylinder have also been reported for different values of S.

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