Tuesday, April 4
Application of thermal boundary conditions at the microscale: A means for flow generation and control
Faculty of Aerospace Engineering at the Technion (Israel)
In marked difference from incompressible fluid flows, microscale gas flows commonly couple the dynamic and thermodynamic fluid descriptions, through the combination of bulk-flow evolution and external boundary conditions. Yet, while the thermal boundary conditions have a significant effect on the generated flows, traditional studies on rarefied gas systems have been limited to gas-surface interactions where the surfaces temperatures are prescribed. Such an assumption, however, seems of little practical value, as the surface temperature at any experimental setup can only be imposed indirectly through a direct prescription of the boundary heat-flux. To examine this observation, the present work demonstrates the impact of replacing an isothermal surface condition with a heat-flux condition in a variety of one-dimensional and unsteady micro-flow setups. These include gas-flow animation problems, acoustic wave propagation, and active flow control applications. Possible extensions to higher-dimension configurations, including shear-driven flows and hydrodynamic instability problems, are also reviewed.
The seminar will take place at 11:00 in classroom 2.1.C19 (Edificio Sabatini) Universidad Carlos III
Wednesday, March 15
Acoustic wave propagation in granular media: rotation and nonlinearities
Granular materials are considered as a complex media when elastic waves propagates in the bulk. This complexity comes from their micro-inhomogeneous character and from the highly nonlinear behavior of the contact between the particles. Compared to the classical elastic solids, one major difference is due to the importance of the rotational degrees of freedom of each particle for the description of the elastic behavior of the media. In this work, the effects of the rotational degrees of freedom are shown through theoretical predictions, numerical simulations and experimental results. Nonlinear wave propagation phenomena also happen in granular materials. Two examples are presented. The first one is the asymmetry of the nonlinear wave generation in a granular crystal submitted to gravity. The second one is the study of one single contact sphere-plane as a nonlinear resonator.
The seminar will take place at 13:00 in classroom 2.1.C19 (Edificio Sabatini) Universidad Carlos III