Base class for flow solvers.

turbigen is CFD-solver agnostic, in that all all pre- and post-processing is done by native code.

Each CFD solver accepts different configuration options. Solver options and their default values are listed below; override the defaults using the solver section of the configuration file.

Adding a new solver only requires functions to save CFD input files, execute the solver, and read back the flow solution into turbigen’s internal data structures. See the Custom solvers section for more details.

ember

ember is the native flow solver built into turbigen.

Parameters

Name	Type	Default	Description
smooth4	float	0.01	Fourth-order smoothing factor.
smooth2_adapt	float	1.0	Second-order smoothing factor, adaptive on pressure.
smooth2_const	float	0.0	Second-order smoothing factor, constant throughout the flow.
smooth_ratio_min	float	0.1	Largest reduction in smoothing on a non-isotropic grid. Unity disables directional scaling, lower values clip the local smoothing factor to be sf_local >= sf * smooth_ratio_min.
CFL	float	0.65	Courant–Friedrichs–Lewy number, time step normalised by local wave speed and cell size. Reduced values are more stable but slower to converge.
n_step	int	5000	Number of time steps to run for.
n_step_mix	int	5	Number of time steps between mixing plane updates.
n_step_dt	int	10	Number of time steps between updates of the local time step.
n_step_log	int	500	Number of time steps between log prints.
n_step_avg	int	1	Number of time steps to average over.
n_step_ramp	int	250	Number of time steps to ramp smoothing and damping.
n_loss	int	5	Number of time steps between viscous force updates.
nstep_damp	int	-1	Number of steps to apply damping.
damping_factor	float	25.0	Negative feedback to damp down high residuals. Lower values are more stable.
Pr_turb	float	1.0	Turbulent Prandtl number.
xllim_pitch	float	0.03	Maximum mixing length as a fraction of the pitch.
precision	int	1	Precision of the solver. 1: single, 2: double.
i_scheme	int	1	Which time-stepping scheme to use. 0: scree, 1: super.
i_loss	int	1	Viscous loss model. 0: inviscid, 1: viscous.
K_exit	float	0.5	Relaxation factor for outlet forcing.
K_inlet	float	0.5	Relaxation factor for inlet forcing.
K_mix	float	0.1	Relaxation factor for mixing plane forcing.
sf_mix	float	0.01	Smoothing factor for uniform enthalpy and entropy downstream of mixing plane.
print_conv	bool	True	Print convergence history in the log.
fmgrid	float	0.2	Factor scaling the multigrid residual.
multigrid	tuple	(2, 2, 2)	Number of cells forming each multigrid level. (2, 2, 2) gives coarse cells of side length 2, 4, and 8 fine cells.
area_avg_Pout	bool	True	Force area-averaged outlet pressure to target, otherwise use uniform outlet pressure.

Custom solvers

To add a new solver, create a new class that inherits from turbigen.solvers.base.BaseSolver. and implement the following methods:

• run(): Run the solver on the given grid and machine geometry.

• robust(): Create a copy of the config with more robust settings.

• restart(): Create a copy of the config with settings to restart from converged solution.

turbigen.solvers.base.BaseSolver is a dataclass, so has an automatic constructor and useful built-in methods. The configuration file solver section is fed into the constructor as keyword arguments and becomes attributes of the instance.