dragonfly_sim.core.RANS_model

Compressible RANS (and laminar Navier-Stokes) at p = 0, built on the Euler model by composition.

CompressibleRANSModel owns a CompressibleEulerModel (self.flow) whose state carries the turbulence model’s transported scalars after the mean flow (rho*nu_tilde for Spalart-Allmaras), and plugs the viscous physics into it. Everything else – spaces, boundary conditions, the Newton solver and positivity limiter, pseudo-transient continuation, time stepping, adjoint and shape-derivative assembly – is the Euler model’s own code. Attributes and methods the RANS model does not define itself are forwarded to self.flow (reads and writes), so DG_windtunnel_model and DG_postprocessor use it exactly like the Euler model.

Discretization (cell-centred finite volume, as DG0)

Inviscid: NS_utils.extended_hll_flux (HLL on the mean flow, the same fan upwinding the scalars), with MUSCL-reconstructed interior-facet traces. Without MUSCL the first-order HLL flux puts acoustic-speed dissipation on the tangential momentum at wall-parallel facets, a numerical viscosity that exceeds the turbulent one through the boundary layer (SA NACA0012 at M 0.7: friction drag ~10x too high).

Viscous: through each facet, F_v(U_f, grad U_f) . n with the reconstructed facet gradient of core/reconstruction.py; no penalty term. Turbulence sources use the Green-Gauss gradient G. G is condensed out of Newton exactly, and is a derived field for adjoints and shape derivatives, as are the cell centres and the wall distance.

Nondimensionalization: rho_inf = p_inf = 1, chord 1, U_inf = M sqrt(gamma), mu_inf = rho_inf U_inf / Re (Re held fixed under set_mach).

Boundary conditions (kind: extra-variable values)

farfield the characteristic state; scalars from the free stream where it: flows in, from the interior where it flows out
wall adiabatic no-slip (define_wall_bc): u = 0, interior density and: internal energy, the turbulence model’s wall values; zero heat flux

slip (symmetry) the Euler slip state, interior scalars, no viscous flux

Solver defaults

Pseudo-transient continuation from the free stream (use_ptc, CFL0 5), one Newton step per pseudo step; FGMRES on the exact condensed Jacobian, preconditioned with ASM(1)/ILU(2) of the compact gradient-frozen part (jacobian_mode “compact_pc”, utils/gradient_condensation.py). Set direct_linear_solver for MUMPS on the exact Jacobian instead.

Classes

CompressibleRANSModel

Module Contents

class dragonfly_sim.core.RANS_model.CompressibleRANSModel(mesh, Re, turbulence_model=None, gamma=1.4, Pr=0.72, Pr_t=0.9, viscosity_law='sutherland', T_inf_dim=300.0, sutherland_S_dim=110.4, muscl=True, limiter=None, limiter_eps=0.01, jacobian_mode='compact_pc')

__getattr__(name)

__setattr__(name, value)

_boundary_scalars(kind, U, inflow)

_extra_scales()

_freestream_extras()

_interior_terms()

_limiter_scales()

_viscous_boundary_terms(U_b, meshtag, kind)

_viscous_time_scale(U)

_wall_stress_arguments(U): (state, gradient) the wall shear is evaluated with: the wall state and the reconstructed facet gradient, exactly what the residual’s wall flux uses.

_wall_traction(U, n)

define_elements_functionspaces()

define_farfield_conditions(bc_dict)

define_noslip_wall_bc(meshtag): Adiabatic no-slip wall. The inviscid flux is the exact flux of the wall state, (0, p n, 0, 0): no mass, energy or scalar flux through the wall, the interior pressure on it. Conduction is dropped from the viscous flux, which is the q.n = 0 condition.

define_wall_bc(meshtag)

eddy_viscosity(U)

eddy_viscosity_ratio(): mu_t / mu of the current state, as a UFL expression.

freestream(): The free-stream dict TurbulenceModel methods take.

laminar_viscosity(U)

noslip_wall_state(U)

set_mach(M)

set_up_solver()

skin_friction_vector(U, n, q_inf): tau_w / q_inf: the wall shear (tangential traction) coefficient vector. Call update_derived_fields() before assembling it.

viscous_flux(U, G, heat_flux=True)

Pr

Pr_t

Re

_OWN

jacobian_mode = 'compact_pc'

limiter = None

limiter_eps = 0.01

mu_inf_const = None

muscl = True

reconstruction = None

sutherland_S_ratio

turbulence_model

viscosity_law = 'sutherland'

wall_distance = None

wall_tags = []