Search NASA⌕ Search

Engineering topics

Hix, W Raphael

Publications and source records attributed to Hix, W Raphael.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

On the character of turbulent-like flows in self-consistent models of core-collapse supernovae

Neutrino-driven convection plays a crucial role in the development of core-collapse supernova (CCSN) explosions. However, the complex mechanism that triggers the shock revival and the subsequent explosion has remained inscrutable for many decades. Multidimensional simulations suggest that the growth of fluid instabilities, especially development of convection, will determine the morphology of the explosion. We have performed 3D simulations using spherical-polar coordinates covering a reduced angular extent (90° computational domain), and with angular resolutions of 2°, 1°, 1/2°, and 1/4°, to study the development of turbulent-like flows in core-collapse supernova explosions on a time scale of order 100 ms. We have employed the multi-physics Chimera code that includes detailed nuclear physics and spectral neutrino transport. Coarse resolution models do not develop an inertial range, presumably due to the bottleneck effect, such that the energy is prevented from cascading down to small scales and tends to accumulate at large scales. High-resolution models instead, start to recover the k −5/3 scaling of Kolmogorov's theory. Stochasticity and few simulation samples limit our ability to predict the development of explosions. Over the simulated time period, our models show no clear trend in improving (or diminishing) conditions for explosion as the angular resolution is increased. However, we find that disordered flow provides an effective pressure, as characterized by the Reynolds stress, behind the shock. This contribution, ~40%–50% of the thermal pressure, aids shock revival and thus the development of the explosion. Finally, we show that the kinetic energy power spectrum of reduced angular extent and full 4π models are consistent, thus indicating that a 90° computational domain is an adequate configuration to study the character of turbulence in CCSNe.

Casanova Bustamante, Jordi↗
DOE OSTI2019

Learning About Nucleosynthesis from Multi-dimensional Simulations of Core-Collapse Supernovae

For more than two decades, we have understood that the development of a successful core-collapse supernova is inextricably linked to neutrino heating and three dimensional fluid flows, with large scale hydrodynamic instabilities allowing successful explosions that spherical symmetry would prevent. Unfortunately, our understanding of the nucleosynthesis that occurs in these supernovae, and therefore the impact of supernovae on galactic chemical evolution, has generally ignored much that we have learned about the central engine of these supernovae over the past two decades. Now, with two and three dimensional simulations of core-collapse supernovae run to sufficient duration, we are learning how the multi-dimensional, neutrino-driven character of the explosions directly impacts the nucleosynthesis and other observables of core-collapse supernovae. Here we focus on lessons from multi-dimensional models which implement realistic nuclear reaction networks.

Hix, W Raphael↗