# Pressure-Entropy SPH¶

A Pressure-Entropy SPH scheme is available in SWIFT, inspired by Hopkins 2013. This includes a fixed Monaghan AV scheme and a Balsara switch.

./configure --with-hydro="pressure-entropy"


The parameters available for this scheme, and their defaults, are:

SPH:
viscosity_alpha: 0.8  # Fixed value for the alpha viscosity


# Pressure-Energy SPH¶

Pressure-energy SPH is now implemented in SWIFT, and like the pressure-entropy scheme it includes a Monaghan AV scheme and a Balsara switch.

./configure --with-hydro="pressure-energy"


The parameters available for this scheme, and their defaults, are:

SPH:
viscosity_alpha: 0.8  # Fixed value for the alpha viscosity


There is a variant of this implementation that includes a Morris & Monaghan (1997) variable artificial viscosity that aims to reduce disappation away from strong shocks. This implementation also includes a Balsara switch. To use this scheme, you should use:

./configure --with-hydro="pressure-energy-monaghan"


The parameters available for this scheme, and their defaults, are:

SPH:
viscosity_alpha: 0.8  # Initial value for the alpha viscosity
viscosity_length: 0.25  # Viscosity decay length (in terms of sound-crossing time)
# These are enforced each time-step
viscosity_alpha_max: 2.0  # Maximal allowed value for the viscosity alpha
viscosity_alpha_min: 0.1  # Minimal allowed value for the viscosity alpha


There is also a compile-time parameter, viscosity_beta that we set to 3.0. During feedback events, the viscosity is set to the compile-time hydro_props_default_viscosity_alpha_feedback_reset = 2.0. These can be changed in src/hydro/AnarchyPU/hydro_parameters.h.