Flow transition to turbulence in the wake of a circular cylinder
Steady incoming flow past a long bluff body is one of the most classical problems in fluid mechanics. In addition to its fundamental significance, this scenario also has various practical applications involving bluff bodies such as offshore platforms and subsea pipelines. In this project, the transition to turbulence in the wake of a circular/square cylinder has been investigated through direct numerical simulations (DNS). Specifically, two main topics have been studied: (i) the wake instabilities of a circular cylinder placed near a plane wall (e.g. the practical scenario of subsea pipelines laid on the seabed), and (ii) the wake transition of a square cylinder, where the influence of the cylinder geometry (circular versus square) is studied
Area of science
Applied Science, Chemistry, Fluid Mechanics
Systems used
Magnus
Applications used
OpenFOAM, Nektar++The Challenge
For the first topic, the wall-bounded boundary layer flow is studied, and the influence on the hydrodynamic forces on the cylinder is examined. This will guide the practical design of subsea pipelines and cables, which is beneficial to Australia’s oil and gas industry. For the second topic, the influence of the cylinder geometry (circular versus square) on the flow characteristics is studied.
To investigate the transient and unstable wake flows of a circular/square cylinder, three-dimensional direct numerical simulations (DNS) are used. High-quality 3D DNS are extremely time-consuming. High computational mesh resolution and long flow time are necessary to capture the flow characteristics. Even by using the supercomputers, this would require a significant amount of computational time. For example, the computational cost for a typical case (at Reynolds number of 1000) on a Cray XC40 supercomputer Magnus up to ~ 400 vortex shedding cycles is ~ 50,000 core hours
The Solution
Direct numerical simulation (DNS) has been adopted for the study of the flow characteristics in the wake of a circular/square cylinder. The numerical simulations were run on Magnus. By analysing the simulated data, a number of flow characteristics have been revealed and the underlying physical mechanisms have been unveiled.
The Outcome
The resources provided by the Pawsey Supercomputing Centre enabled the expensive 3D numerical simulations to be carried out. In particular, the use of Magnus allows large-scale simulations to be carried out with highly parallelised computation (~ 200 – 500 cores).
Two high-quality journal papers and one conference paper have been published in 2018 based on this project, with the acknowledgement of the Pawsey Supercomputing resources.
List of Publications
1. Jiang, H., Cheng, L., 2018. Hydrodynamic characteristics of flow past a square cylinder at moderate Reynolds numbers. Physics of Fluids 30, 104107.
2. Jiang, H., Cheng, L., An, H., 2018. Three-dimensional wake transition of a square cylinder. Journal of Fluid Mechanics 842, 102–127.
3. Tong, F., Cheng, L., An, H., Griffiths, T., 2018. Hydrodynamics on circular cylinder close to a wall: Effects from wall boundary layers. Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering – OMAE
