1. CITA|ICAT Jonathan Dursi HPCS’06 15 May Towards Understanding some Astrophysical Flows using Multiscale Simulations with the FLASH code Jonathan Dursi, Chris Thompson, Daniel Doucette, Christine Hiratsuka

2. CITA|ICAT Jonathan Dursi HPCS’06 15 May Outline ● The FLASH code ● Problems of interest: disk-wind, turbulent ignition – AMR can’t save us ● Multiscale approach ● Progress so far

3. CITA|ICAT Jonathan Dursi HPCS’06 15 May The Flash Code Cellular detonation Compressed turbulence Helium burning on neutron stars Richtmyer-Meshkov instability Laser-driven shock instabilities Nova outbursts on white dwarfs Rayleigh-Taylor instability Flame-vortex interactions Gravitational collapse/Jeans instability Wave breaking on white dwarfs Shortly: Relativistic accretion onto NS Orzag/Tang MHD vortex Type Ia Supernova Intracluster interactions Magnetic Rayleigh-Taylor

4. CITA|ICAT Jonathan Dursi HPCS’06 15 May Cellular detonation Compressed turbulence Helium burning on neutron stars Richtmyer-Meshkov instability Laser-driven shock instabilities Nova outbursts on white dwarfs Rayleigh-Taylor instability Flame-vortex interactions Gravitational collapse/Jeans instability Wave breaking on white dwarfs Shortly: Relativistic accretion onto NS Orzag/Tang MHD vortex Type Ia Supernova Intracluster interactions Magnetic Rayleigh-Taylor FLASH code: Explicit reactive hydrodynamics code AMR, massively parallel Scales very well Highly portable Used, tested on wide variety of problems Rigorously tested Modular (easy to add/change physics modules) Widely available (http://flash.uchicago.edu) The Flash Code

5. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● AMR, no time refinement (no efficiency gains for our problems) ● Main hydro package – PPM (good for supersonic/near sonic flows) ● Tested against laboratory instability experiments ● Regression tests run nightly – crucial for maintaining confidence on constantly-developed code The Flash Code – Some Details

6. CITA|ICAT Jonathan Dursi HPCS’06 15 May Turbulence is Hard ● Separation of scales, but no locality ● Sometimes easy(ish) to model small scales ● Sometimes small scales matter – Interactions with other physics – Fluctuations themselves

7. CITA|ICAT Jonathan Dursi HPCS’06 15 May Central object (young star, proto-NS,..) Fast wind Cold, opaque, rotating disk Interaction of Accretion Disk with Wind

8. CITA|ICAT Jonathan Dursi HPCS’06 15 May Formation of turbulent boundary layer Fast wind Cooling (more efficient at higher temp, lower dens) Gravity (to central object) What is structure of top layer of disk?

9. CITA|ICAT Jonathan Dursi HPCS’06 15 May What is structure of top layer of disk? ● Turbulent boundary layer determines – Top BC of disk – Transport vertically through disk ● Mass ● Radiation – Whether disk survives wind

10. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● Time, length scales of developing boundary locally much smaller than global wind scales ● Must resolve much of turbulence to determine interaction of turbulence w/ cooling ● Onset: 2D. Full nonlinear development: 3D Interaction of Accretion Disk with Wind

11. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● Approach: – Model large range of parameters of small- scale turbulent bounary – Build library of resulting boundary layers, transport – Use as subgrid model for large-scale simulation Interaction of Accretion Disk with Wind

12. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● Burning of C/O white dwarf ● Ignition in a turbulent medium ● Number, size of ignition points shapes explosion ● Ignition points are turbulent fluctuations Turbulent simmering WD core (rotating, convective) Turbulent temperature fluctuations (`hotspots’) Turbulent ignition of Type Ia supernovae

13. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● White dwarf: ~3000 km ● Integral turbulence scale: ~400 km ● Simmering feeds back into turbulence. ● Fluctuations can ignite: mm to cm. Turbulent ignition of Type Ia supernovae

14. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● Opposite situation of wind/disk: – Turbulence is large scale – Want effect of large scale flows on small scale physics ● For given turbulence intensity, how does ignition happen? Turbulent ignition of Type Ia supernovae

15. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● Many 1d spherical simulations of igniting hotspots ● Determine `flammability limits’ ● Highly nonlinear ● Non-igniting hotspots contribute little energy to flow Turbulent ignition of Type Ia supernovae

16. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● Large 1d, 3d simulations of compressible reactive turbulence ● Extract temperature, hotspot PDF ● Need large simulations – ignition points are necessarily rare events Turbulent ignition of Type Ia supernovae

17. CITA|ICAT Jonathan Dursi HPCS’06 15 May ● Development of subgrid models useful way to approach some very challenging problems ● Even where large simulations are needed small scale simulations to build/calibrate SGS take bulk of computational time ● Initial models being developed using simplified SGS, more work necessary Progress/Summary