seminaris en mecànica de fluids

Fluid Mechanics Across Scales

by

Professor Dimitris Drikakis
University of Strathclyde
Glasgow, UK

This seminar concerns recent advances in high-resolution computational fluid dynamics methods (CFD) and multi-scale models, and their implementation in both fundamental and industrially relevant flows across a range of physical scales.

The first part of the seminar will provide a brief introduction to high-resolution Large Eddy Simulation; discuss improvements of CFD methods for compressible turbulent flows; and present results for aeronautical/aerospace flows covering a broad range of selective case studies, including: low and high speed unsteady separated flows around aerospace configurations; compressible boundary layers; acoustic loading associated with transitional and turbulent boundary layers; and compressible turbulent mixing in multi-component flows.

Transition to complex dynamics in the cubic lid-driven cavity

by

Professor Juan M. Lopez
co-authors: Bruno D. Welfert, Ke Wu and Jason Yalim
School of Mathematical and Statistical Sciences,
Arizona State University, Tempe AZ 85287, USA

The onset of time dependence in the cubic lid-driven cavity is surprisingly complicated, given the simplicity of the geometry and the modest value of the Reynolds number at which it occurs. The onset is characterized by finite amplitude oscillations which appear to be stable for long times, but are subjected to intermittent bursts at irregular times during which the reflection symmetry about the spanwise midplane is broken. The complex dynamics are shown to be intimately related to the subcritical nature of the instability of the steady basic state. We use a spectral collocation numerical technique, solving both in the full three-dimensional space as well as in the symmetric subspace, and use selective frequency damping and Arnoldi iterations about the unstable basic state to determine its bifurcations. Edge tracking is also used to investigate a number of time-dependent saddle states. Putting all this together, we show that the complex dynamics are organized by two successive Hopf bifurcations, the first of which is shown to be subcritical.  All local states are unstable in the full space at higher Reynolds numbers, leading to the intermittent bursting behavior.