Search

Large-eddy simulations of a subsonic three-dimensional cavity flow with self-sustaining oscillations are carried out for a Reynolds number based on the length of the cavity equal to . Meticulous comparisons with available experimental data corresponding to the same configuration demonstrate a high level of accuracy. Special attention is paid to the mixing layer that develops over the cavity and two different zones are identified. The first one is dominated by Kelvin–Helmholtz instability, and the linear as well as quadratic energy transfers leading to the filling of velocity spectra are described. The Kelvin–Helmholtz instability also appears to be forced near the origin of the layer, and it is postulated that the small recirculation bubble located in this area is responsible for the forcing. Downstream of the first zone and up to the vicinity of the aft wall, the layer behaves very similarly to a free mixing layer by exhibiting a linear spreading. An influence of the recirculating flow inside the cavity upon the growth of the layer is nevertheless observed at downstream stations. Analysis of the pressure on the floor of the cavity reveals that the self-sustaining oscillation-related pressure modes (Rossiter modes) are independent of their spanwise location inside the cavity. On the contrary, Rossiter modes exhibit streamwise modulations and it is demonstrated that a very simple two-wave model is able to reproduce the spatial shape of the modes. Nonlinear interactions between Rossiter modes are encountered, as well as nonlinear interactions with low-frequency components. A joint time–frequency analysis shows a temporal modulation of the Rossiter mode levels at similar low frequencies, resulting in a special form of intermittency with competitive energy exchanges between modes.

The temporal evolution of the three-dimensional structure of a plane mixing layer is investigated by Direct Numerical Simulation. Detailed visualizations are produced of the interactions between spanwise rolls, initiated by the Kelvin-Helmholtz instability, and the longitudinal ribs formed in the braid region, these interactions leading to the formation of smaller structures. Using 3D wavelet analysis, the spatial coherent structures of the vorticity field are related to the different scales produced in the Fourier spectrum. A detailed analysis of the vorticity amplification mechanisms by stretching is provided which supports the theoretical model given recently by Moffat, Kida and Ohkitani. The topologies of stretching and energy dissipation zones are related to the production of small scales during the rib formation and the bending of the rolls. This analysis suggests a possible generic mechanism for small scale production.

Symmetries are transformations which act on the physical variables of a system. They can transform the time, the position, the velocity and the thermodynamical properties (density, pressure) of the physical system. But they do not modify the evolution of the physical system. This work deals with continuous symmetries which are described by the Lie group theory. In physics, symmetries are space-time transformations, such as the Galilean transformations, the Lorentz transformations, the projective transformations, the scaling transformations, the translations.

Reference EPFL-ARTICLE-161249doi:10.1007/s10494-007-9118-yView record in Web of Science Record created on 2010-11-30, modified on 2016-08-09

Keywords: ecoulement : tridimensionnel ; ecoulement : instationnaire ; ecoulement : laminaire ; simulation ; ecoulement : incompressible Reference Record created on 2005-11-18, modified on 2016-08-08