Ajaykumar Rajasekharan

Application of a Dynamic Variational Multiscale Method to the LES of Separated Turbulent Flows

The objective of this paper is to report on the ability of the recently developed dynamic variational multiscale LES (dynamic VMS-LES) method 1 to simulate unsteady, separated, turbulent flows. To this end, three problems are considered. The first one is associated with a low speed, high angle of attack flow over a forward swept scaled wing. It is representative of a flow regime that is typically encountered in Micro Air Vehicle (MAV) applications. The second problem focuses on the flow over a pitching NACA-0012 wing and benchmarks the performance of the dynamic VMS-LES method at predicting large scale unsteady separation and lift/moment hysteresis. The last test case is a subcritical flow over a sphere, which is depictive of an important class of separated flows where the location of the flow detachment is not determined by geometry. In each case, the results predicted by the dynamic VMS-LES method are compared to those obtained with other turbulence models and to experimental data. In most cases, the dynamic VMS-LES is found to perform better than the other considered static and dynamic LES models.

Effects of Varied Physical Mechanisms on the Evolution of Lubricant Interface During Heat-Assisted Magnetic Recording

A concoction of various forces and physical effects (both mechanical and chemical) come into play in the depletion and evolution of the lubricant on the media during a heat-assisted magnetic recording (HAMR) process. They include the air-bearing shear and pressure, capillary pressure, thermo-capillary stress, disjoining pressure, lubricant desorption and the vapor recoil mechanism. The effects of these mechanisms and their complex interplay to stabilize/destabilize the lubricant interface is studied here numerically. Results for Z-type perfluropolyether (PFPE) lubricants with different polydispersity indices (PDI) are summarized.Copyright