Simulation Enabled Discoveries: Examples from MHD and Turbulence
Speaker: Ravi Samtaney, The King Abdullah University of Science and Technology
Presentation
Abstract
Computation has emerged as the indispensable third leg of scientific discovery along with the traditional two branches of theory and experiment. In this talk we discuss some case studies from magnetohydrodynamics (MHD) and fluid turbulence.
Our first example is that of magnetic suppression of the Richtmyer-Meshkov instability (RMI). In hydrodynamics, a density interface separating two fluids is unstable under impulsive acceleration. This instability aka RMI has been the bane of inertial confinement fusion where it is considered highly detrimental. We present a vortex dynamical interpretation of the instability and show that, in MHD, the baroclinic vorticity generated on the interface is carried away by slow-mode MHD shocks leading to stabilization.
The second example is that of magnetic reconnection (MR). Loosely defined, MR is the breaking and reattachment of magnetic field lines, and is a somewhat ubiquitous phenomenon in our universe: it accompanies coronal mass ejections from our Sun, observed in the earth’s magneto-tail, etc. Standard quasi-steady models in single-fluid resistive MHD severely under predict the reconnection rate compared with observations. A key-missing piece of physics is an instability dubbed the plasmoid instability. Large-scale simulations led to the discovery, that for Lundquist number greater than 104, the reconnection rate saturates due to plasmoids.
A third example pertains to the question whether the mean velocity profile in a wall-bounded turbulence obeys a log-law or a power-law. Our simulations results provide strong evidence that turbulence gravitates naturally towards the log-law scaling at extremely large Reynolds numbers.
We believe these case studies amply demonstrate that simulation enabled discoveries are no longer a myth, and that computations are a legitimate tool to answer clearly posed questions in science and engineering.
Biography
Ravi Samtaney is presently a professor in Mechanical Engineering (Physical Science and Engineering Division) with a joint appointment in Applied Mathematics & Computational Science at the King Abdullah University of Science and Technology (KAUST) in the Kingdom of Saudi Arabia. He serves as Chair of the ME Program and Associate Dean of the PSE Division. Prior to KAUST, he was a Research Physicist at the Princeton Plasma Physics Laboratory, Princeton University, and a research faculty at the California Institute of Technology, and worked at NASA Ames Research Center. His research is at the intersection of applied mathematics, physics, and engineering, from fundamental processes in fluid mechanics (shocks, turbulence, ablation, ionization, etc.) to numerical methods and large-scale computing (adaptive meshing, scalable solvers, software engineering, etc.). He obtained his Ph.D. from Rutgers University in 1994.