Large eddy simulation of flow past a circular cylinder of low aspect ratio (AR = 1 and 3), spanning subcritical, critical and supercritical regimes, is carried out for 2 × 103 ≤ Re ≤ 4 × 105. The end walls restrict three-dimensionality of the flow. The critical Re for the onset of the critical regime is significantly lower for small aspect ratio cylinders. The evolution of secondary vortex (SV), laminar separation bubble (LSB) and the related transition of boundary layer with Re is investigated. The plateau in the surface pressure due to LSB is modified by the presence of SV. Proper orthogonal decomposition of surface pressure reveals that although the vortex shedding mode is most dominant throughout the Re regime studied, significant energy of the flow lies in a symmetric mode that corresponds to expansion–contraction of the vortex formation region and is responsible for bursts of weak vortex shedding. A triple decomposition of the time signals comprising of contributions from shear layer vortices, von Kármán vortex shedding and low frequency modulation due to the symmetric mode of flow is proposed. A moving average, with appropriate size of window, is utilized to estimate the component due to vortex shedding. It is used to assess the variation, with Re, of strength of vortex shedding as well as its coherence along the span. Weakening of vortex shedding in the high subcritical and critical regime is followed by its rejuvenation in the supercritical regime. Its spanwise correlation is high in the subcritical regime, decreases in the critical regime and improves again in the supercritical regime.
Bibliographical noteKAUST Repository Item: Exported on 2021-11-20
Acknowledgements: The authors acknowledge the use of the High Performance Computational (HPC) facility at Indian Institute of Technology Kanpur (IITK), Cray XC-40, Shaheen, at King Abdullah University of Science and Technology (KAUST), Saudi Arabia, and National PARAM Supercomputing Facility (NPSF) at the Centre of Development of Advanced Computing (C-DAC), Pune, India. The authors would like to thank Professor R. Samtaney of KAUST for his help with access to the computational facility at KAUST. The HPC facility at IITK was established with the assistance of Department of Science and Technology (DST), India. The authors would like to thank Mr M. Furquan and Mr A. Desai for their help in carrying out POD. The authors are grateful to the reviewers for their insightful suggestions and inputs towards the improvement of this paper.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.
ASJC Scopus subject areas
- Mechanics of Materials
- Mechanical Engineering
- Condensed Matter Physics