6 research outputs found
Instabilities in the wake of an inclined prolate spheroid
We investigate the instabilities, bifurcations and transition in the wake
behind a 45-degree inclined 6:1 prolate spheroid, through a series of direct
numerical simulations (DNS) over a wide range of Reynolds numbers (Re) from 10
to 3000. We provide a detailed picture of how the originally symmetric and
steady laminar wake at low Re gradually looses its symmetry and turns unsteady
as Re is gradually increased. Several fascinating flow features have first been
revealed and subsequently analysed, e.g. an asymmetric time-averaged flow
field, a surprisingly strong side force etc. As the wake partially becomes
turbulent, we investigate a dominating coherent wake structure, namely a
helical vortex tube, inside of which a helical symmetry alteration scenario was
recovered in the intermediate wake, together with self-similarity in the far
wake.Comment: Book chapter in "Computational Modeling of Bifurcations and
Instabilities in Fluid Dynamics (A. Gelfgat ed.)", Springe
Influence of turbulence closure models on the vortical flow field around a submarine body undergoing steady drift
Manoeuvring underwater vehicles experience complex three-dimensional flow. Features include stagnation and boundary layer separation along a convex surface. The resulting free vortex sheet rolls up to form a pair of streamwise body vortices. The track and strength of the body vortex pair results in a nonlinear increase in lift as body incidence increases. Consequently, accurate capture of the body vortex pair is essential if the flow field around a manoeuvring submarine and the resulting hydrodynamic loading is to be correctly found. This work highlights the importance of both grid convergence and turbulence closure models (TCMs) to the strength and path of the crossflow-induced body vortices experienced by the DOR submarine model at an incidence angle of 15°. Five TCMs are considered; Spalart–Allmaras, k-?, k-?, shear stress transport, and the SSG Reynolds stress model. The SSG Reynolds stress model shows potential improvements in predicting both the path and strength of the body vortex over standard one- and two-equation TCMs based on an eddy viscosity approach<br/