Particle coherent structures in incompressible fluid flows
The motion of small particles in incompressible steady flows can be strongly characterized by the creation of particle attractors. Several dissipative mechanisms may lead to the accumulation of particles, such as inertial forces due to the particle-fluid density mismatch or to finite-size effects in the bulk. Other dissipative effects which may lead to attractors are due to gravity and Basset history forces. The particle accumulation mechanism of interest in this talk relies on the interaction of the particles with undeformable boundaries, very frequent in boundary-driven flows. For dilute suspensions, these accumulation phenomena are successfully modeled as single-particle attractions and are strongly correlated to the topology of the fluid flow without particles. When the accumulations are in form of periodic or quasi-periodic patterns, they are termed finite-size Lagrangian coherent structures, since they are the result of the Lagrangian topology of the fluid flow and of the finite-size effect of the particle near the boundary. Boundary-driven flows will be considered to demonstrate the relative importance of the several dissipation mechanisms which affect the particle motion. A comparison between numerical simulations and experiments will be presented to further strengthen the theoretical understanding of finite-size Lagrangian coherent structures.
Operating Range Limitations in High Speed Compressors
Xavier Ottavy is a Research Director at CNRS (National Centre for the Scientific Research) in France. Since 2016, he is at the Head of the Turbomachinery Department at LMFA (Laboratoire of Fluid Mechanics and Acoustics) located at the Ecole Centrale de Lyon (ECL) in France. His research fields concern mostly the study of compressors (axial, multi-stage, Low and High Pressure, UHBR fans) using high power experimental test rigs (until 3 MegaWatts) and CFD.
Dynamic Triad Interactions and the Evolution of Turbulent Power Spectra
Clara Marika Velte is Associate Professor at the Technical University of Denmark in the Department of Mechanical Engineering.