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Installation & Setup

Disk Initial Conditions

Disk Initial Conditions

Sailfish currently supports three hydrodynamic initial conditions, including the one used in the Santa Barbara Code Comparison, and the viscous spreaing ring described in the classic Pringle (1981) review article. Note that the hydrodynamic initial condition type is controlled by the configuration keyword setup (this might change to a better name such as disk_ic in the future).

Supported Initial Disk Types

  • setup=ring

    Pringle Viscous Ring - A circular ring of gas at unit separation from the central object

    Used for testing numerical accuracy and rate of convergence. Note that the tstart configuration item determines the ring width at the start of the simulation. Works only with the constant-nu viscosity model.

  • setup=steady

    Equilibrium Accretion Disk - An effectively infinite, axisymmetric steady-state viscous flow

    The disk initially extends from the outer domain radius to the origin (or the inner domain radius in polar mesh mode). Constant-alpha and constant-nu viscosity models are supported.

  • setup=kitp

    Binary Disk Interactions - The initial condition used in the Santa Barbara Code Comparison from Duffell et al. (2024)

    This initial condition includes a low-density cavity around around the binary, and a small perturbation to seed growth of the eccentric disk mode.

Binary Disk Simulations

Equal Mass Binary System

Binary Disk Evolution

Configuration: Equal mass binary • sink_size = 0.05 • nu = 10⁻³

Binary Evolution

Binary disk evolution showing gap formation and spiral wave propagation - Madeline Clyburn
The disk develops a central cavity as gravitational torques clear material near the binary. Spiral density waves propagate outward, redistributing angular momentum throughout the disk.

Binary Black Hole Merger

Gravitational Wave Phase

Configuration: Merger evolution • GW inspiral • Same disk parameters

Merger Evolution

Binary merger simulation showing inspiral and final coalescence - Madeline Clyburn
The binary separation decreases following GW inspiral until merger at t=0. The disk responds dynamically to the changing gravitational potential, exhibiting complex flow patterns.

Following Secondary BH in a Binary

Numerical Considerations

Configuration: sink_size = 0.2 • rsoft = 10.0 • Focus on secondary BH

Softened Potential

Binary simulation showing the secondary BH scraping the inner edge of the circumbinary disk - Akhil Nair
In this simulation the gravitational softening length is 10x bigger than the base configuration

Configuration Details

Central Object Types

Single Black Hole
central_object = single
sink_size = 0.05
sink_rate = 10.0

Perfect for studying isolated accretion disks around single compact objects.

Binary System
central_object = binary
mass_ratio = 1.0      # Equal mass
a = 1.0               # Separation
sink_size = 0.05

Ideal for circumbinary disk studies and gravitational wave astronomy.

Inspiral & Merger
central_object = merger
mass_ratio = 1.0
tstart = -100         # Start during inspiral
tfinal = 10           # Continue post-merger

Advanced scenarios for pre/post-merger disk evolution studies.

Physics Parameters

Key Physical Scales

Parameter Typical Value Physical Meaning
nu 10⁻³ Kinematic viscosity
sink_size 0.05 - 0.2 Accretion region size
rsoft 1.0 - 10.0 Gravitational softening length
mass_ratio 0.1 - 1.0 Secondary/primary mass ratio

Simulation Goals

Method Validation: Use Ring setup with analytical solutions

Astrophysical Modeling: Binary/merger setups for GW astronomy

Parameter Studies: Vary nu, sink_size, rsoft systematically

Comparative Analysis: Different central object configurations

Getting Started

Quick Start Guide

  1. Choose your setup based on research goals
  2. Configure parameters using the preset files in /presets/
  3. Run simulation: ./bin/sailfish_gpu presets/your_setup.cfg
  4. Analyze results using the diagnostic outputs

View Presets Numerical Methods