Numerical study of turbulent manoeuvring-body wakes: Interaction with a non-deformable free surface

Abstract

Direct numerical simulation (DNS) is used to investigate the development of a turbulent wake created by an impulsively accelerating axisymmetric self-propelled body below a non-deformable free surface. The manoeuvring body is represented by the combination of an immersed boundary method and a body force. The Reynolds number based on either the diameter of the virtual body or the jet forcing intensity is relatively high (O(1000)), corresponding to the fully turbulent case. The vertical growth of the coherent structure behind the body is restricted by the upper and lower stress-free layers, and the wake signatures are observed to penetrate to the free surface. The late-time behaviour of the dipole induced due to vertical confinement can be predicted by scaling laws, also relevant to a stratified fluid.

Keywords:

• direct numerical simulation
• manoeuvring-body wake
• vortex dipole

Acknowledgments

[Acknowledgements] The authors gratefully acknowledge Prof. Sergey Voropayev for his invaluable comments and suggestions. This work was funded by the UK Engineering and Physical Sciences Research Council (EPSRC) (grant EP/G05035X), as part of the UK Turbulence Consortium (grant EP/G069581/1). The simulations were run on the University of Southampton Iridis 3 cluster and HECToR, the UK’s national high-performance computing service, which is provided by UoE HPCx Ltd at the University of Edinburgh, Cray Inc. and NAG Ltd, and funded by the Office of Science and Technology through EPSRC’s High End Computing programme.