test_flow_around_sphere.py 5.08 KB
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import pytest
import numpy as np

from lbmpy.advanced_streaming import BetweenTimestepsIndexing, Timestep, get_timesteps
from lbmpy.creationfunctions import create_lb_function, create_lb_collision_rule, create_lb_method
from lbmpy.boundaries import LatticeBoltzmannBoundaryHandling, NoSlip, UBB

from lbmpy.relaxationrates import relaxation_rate_from_lattice_viscosity
from lbmpy.macroscopic_value_kernels import pdf_initialization_assignments
from lbmpy.stencils import get_stencil

from pystencils import create_kernel, create_data_handling, Assignment
from pystencils.slicing import slice_from_direction, get_slice_before_ghost_layer


@pytest.mark.parametrize('stencil', ['D2Q9', 'D3Q19', 'D3Q27'])
@pytest.mark.parametrize('galilean_correction', [False, True])
@pytest.mark.longrun
def test_flow_around_sphere(stencil, galilean_correction):

    if galilean_correction and stencil != 'D3Q27':
        return True

    pytest.importorskip('pycuda')

    stencil = get_stencil(stencil)
    dim = len(stencil[0])
    Q = len(stencil)

    target = 'gpu'
    streaming_pattern = 'aa'
    timesteps = get_timesteps(streaming_pattern)

    L_LU = 20
    u_max = 0.05
    Re = 5000

    kinematic_viscosity = (L_LU * u_max) / Re
    initial_velocity = (u_max, ) + (0, ) * (dim - 1)

    omega_v = relaxation_rate_from_lattice_viscosity(kinematic_viscosity)

    channel_size = (30 * L_LU, ) + (100,) * (dim - 1)
    sphere_position = (channel_size[0] // 3,) + (channel_size[1] // 2,) * (dim - 1)
    sphere_radius = L_LU // 2

    method_params = {
        'stencil': stencil,
        'method': 'cumulant',
        'relaxation_rate': omega_v,
        'galilean_correction': galilean_correction
    }

    optimization = {
        'target': target,
        'pre_simplification': True
    }

    lb_method = create_lb_method(optimization=optimization, **method_params)

    def get_extrapolation_kernel(timestep):
        boundary_assignments = []
        indexing = BetweenTimestepsIndexing(
            pdf_field, stencil, streaming_pattern=streaming_pattern, prev_timestep=timestep)
        f_out, _ = indexing.proxy_fields
        for i, d in enumerate(stencil):
            if d[0] == -1:
                asm = Assignment(f_out.neighbor(0, 1)(i), f_out.center(i))
                boundary_assignments.append(asm)
        boundary_assignments = indexing.substitute_proxies(
            boundary_assignments)
        iter_slice = get_slice_before_ghost_layer((1,) + (0,) * (dim - 1))
        extrapolation_ast = create_kernel(
            boundary_assignments, iteration_slice=iter_slice, ghost_layers=1, target=target)
        return extrapolation_ast.compile()

    dh = create_data_handling(channel_size, periodicity=False, default_layout='fzyx', default_target=target)

    u_field = dh.add_array('u', dim)
    rho_field = dh.add_array('rho', 1)
    pdf_field = dh.add_array('pdfs', Q)

    dh.fill(u_field.name, 0.0, ghost_layers=True)
    dh.fill(rho_field.name, 0.0, ghost_layers=True)

    dh.to_gpu(u_field.name)
    dh.to_gpu(rho_field.name)

    optimization['symbolic_field'] = pdf_field

    bh = LatticeBoltzmannBoundaryHandling(lb_method, dh, pdf_field.name,
                                          streaming_pattern=streaming_pattern, target=target)
    wall = NoSlip()
    inflow = UBB(initial_velocity)

    bh.set_boundary(inflow, slice_from_direction('W', dim))

    directions = ('N', 'S', 'T', 'B') if dim == 3 else ('N', 'S')
    for direction in directions:
        bh.set_boundary(wall, slice_from_direction(direction, dim))

    outflow_kernels = [get_extrapolation_kernel(Timestep.EVEN), get_extrapolation_kernel(Timestep.ODD)]

    def sphere_boundary_callback(x, y, z=None):
        x = x - sphere_position[0]
        y = y - sphere_position[1]
        z = z - sphere_position[2] if z is not None else 0
        return np.sqrt(x**2 + y**2 + z**2) <= sphere_radius

    bh.set_boundary(wall, mask_callback=sphere_boundary_callback)

    init_eqs = pdf_initialization_assignments(lb_method, 1.0, initial_velocity, pdf_field,
                                              streaming_pattern=streaming_pattern,
                                              previous_timestep=timesteps[0])
    init_kernel = create_kernel(init_eqs, target=target).compile()

    output = {
        'density': rho_field,
        'velocity': u_field
    }

    lb_collision_rule = create_lb_collision_rule(lb_method=lb_method, output=output, optimization=optimization)

    lb_kernels = []
    for t in timesteps:
        lb_kernels.append(create_lb_function(collision_rule=lb_collision_rule, optimization=optimization,
                                             streaming_pattern=streaming_pattern, timestep=t))

    timestep = timesteps[0]

    dh.run_kernel(init_kernel)

    total_steps = 5000
    stability_check_frequency = 1000

    for i in range(total_steps):
        bh(prev_timestep=timestep)
        dh.run_kernel(outflow_kernels[timestep.idx])
        timestep = timestep.next()
        dh.run_kernel(lb_kernels[timestep.idx])

        if i % stability_check_frequency == 0:
            dh.to_cpu(u_field.name)
            assert np.isfinite(dh.cpu_arrays[u_field.name]).all()