nsfds2 0.9.1

Finite difference solver for Navier-Stokes equations

nsfds2 : 2D Navier-Stokes Finite Differences Solver

Introducing nsfds2

nsfds2 is 2D Navier-Stokes Solver that uses finite difference method. In particular, nsfds2 is specialized in acoustic simulations.

nsfds2 is still in developpement. It is still full of bugs and comes with ABSOLUTELY NO WARRANTY.

Dependencies

• python > 3.6
• numpy
• matplotlib
• h5py
• progressbar33
• ofdlib2 >= 0.9.3
• fdgrid >= 0.8.0
• mplutils >= 0.3.0

Installation

python setup.py install

or

pip install nsfds2

Note: To compile ofdlib2, OS X users may recquire :

xcode-select --install

Classical use

nsfds2 can be used from a terminal with :

nsfds2 solve|movie|show

• solve : solves Navier-Stokes equation using default config file ~/.nsfds2/nsfds.conf
• movie : makes movie from results obtained with solve subcommand
• show : set of commands for simulations parameters and grid inspection

See -h option for further help :

nsfds2 solve -h
nsfds2 movie -h
nsfds2 show -h

Custom Use

nsfds2 can also be used as a classical Python package. It provides several main objects to perform numerical simulations :

• init package povides :

  • CfgSetup class : Parses all simulation parameters from ~/.nsfds2/nsfds2.conf file.
  • Fields class : Initialize all simulation parameters and fields

• fdtd module provides FDTD class : Execute simulation

• utils package provides in paricular graphics module to make result post-treatment

The following example gives the general philosophy to use nsfds2 :

import matplotlib.pyplot as plt
from nsfds2.init import CfgSetup, Fields
from nsfds2.fdtd import FDTD
from fdgrid.mesh import Mesh

# Read simulation parameter in config file ~/nsfds2/nsfds2.conf
cfg = CfgSetup()

# Define the mesh
msh = Mesh((cfg.nx, cfg.nz), (cfg.dx, cfg.dz), origin=(cfg.ix0, cfg.iz0), obstacles=[])

# Init acoustic fields
fld = Fields(msh, cfg)

# Create simulation
fdtd = FDTD(msh, fld, cfg)
fdtd.run()

# Figures
plt.figure()
plt.imshow(fld.p)
plt.show()

Config file

By default, nsfds2 create the config file ~/.nfds2/nsfds2.conf. This file contains simulation parameters that are used by the solver.

[configuration]
timings = True|False 			# Display timings
quiet = True|False 			# Quiet mode

[simulation]
nt = 500 				# Number of time iterations
ns = 10 				# Save each ns iterations
cfl = 0.5 				# Courant–Friedrichs–Lewy number

[geometry]
mesh = regular|curvilinear|adaptative	# Mesh type
file = None|path 			# Path to python file (for geoname and curvname)
geoname = helmholtz_double 		# Python function for geometry
curvname = curvz			# Python function for curvilinear coordinates
bc = ARRA 				# Boundary conditions. Must be a mix of ARP
nx = 256				# Number of grid points along x-axis
nz = 256				# Number of grid points along z-axis
ix0 = 128 				# Origin of the grid
iz0 = 0					# Origin of the grid
dx = 1e-4				# Spatial x-step
dz = 1e-4 				# Spatial z-step

[PML]
beta = 0.0 				# Depends on pseudo mean flow profile
alpha = 4.0 				# Order of the spatial repartition law
sigmax = 20|auto 			# Filter strength along x. Can be 'auto'
sigmaz = 20|auto 			# Filter strength along z. Can be 'auto'
npml = 15				# Number of points of the PML

[source]
type = None|pulse|harmonic|white 	# Source type
ixs = 64				# Source x-location
izs = 128 				# Source z-location
s0 = 1e6 				# Sources strength [Pa]
B0 = 2 					# Half spatial bandwidth
f0 = 60000 				# Frequency (only for harmonic) [Hz]

[flow]
type = None 				# Flow type
U0 = 5 					# Flow velocity following x [m/s]
V0 = 5 					# Flow velocity following z [m/s]

[eulerian fluxes]
stencil = 3|7|11 			# Number of points of stencil

[filtering]
filter = True|False 			# Activate selective filter
stencil = 11 				# Number of points of stencil used by filters
stength = 0.75 				# Strength of the filter

[viscous fluxes]
viscosity = True|False 			# Activate viscosity
stencil = 7 				# Number of points of stencil used for viscosity

[shock capture]
shock capture = True|False 		# Activate shock capture procedure
stencil = 7 				# Number of points of stencil for capture
method = pressure|dilatation 		# Capture based on pressure or dilatation

[figures]
figures = True|False 			# Activate figures
probes = True|False 			# Show probes in maps
pml = True|False 			# Show PML in maps

[save]
save = True|False 			# Activate save
path = results 				# Path to data file
filename = tmp 				# Data filename
compression = None|lzf 			# Activate compression
probes = [[128, 128], [128, 192]] 	# Probe locations. Must be a list of lists

Examples

The docs directory gathers some configuration files example. Copy one of these files to .nsfds2/nsfds2.conf and :

nsfds2 solve

Known Bugs

• Mean flows are not yet fully supported.
• When using Curvilinear meshes, PML, viscous flux, and moving boundaries are not properly calculated. Be careful with the validity of the results !