Decaying Homogeneous Isotropic Turbulence - 2D

In this example we consider decaying homogeneous isotropic turbulence, similar to the cases considered in [2] and [3]. The initial velocity field is created randomly, but with a specific energy spectrum. Due to viscous dissipation, the turbulent features eventually group to form larger visible eddies.

Packages

We just need IncompressibleNavierStokes and a Makie plotting backend.

using CairoMakie
using IncompressibleNavierStokes
# using CUDA

Setup

n = 256
ax = LinRange(0.0, 1.0, n + 1)
setup = Setup(;
    x = (ax, ax),
    boundary_conditions = (;
        u = ((PeriodicBC(), PeriodicBC()), (PeriodicBC(), PeriodicBC())),
    ),
    # backend = CUDABackend(),
)
u = random_field(setup, 0.0);

Solve unsteady problem

state, outputs = solve_unsteady(;
    setup,
    start = (; u),
    tlims = (0.0, 1.0),
    params = (; viscosity = 2.5e-4),
    processors = (
        rtp = realtimeplotter(; setup, nupdate = 10),
        ehist = realtimeplotter(;
            setup,
            plot = energy_history_plot,
            nupdate = 10,
            displayfig = false,
        ),
        espec = realtimeplotter(;
            setup,
            plot = energy_spectrum_plot,
            nupdate = 10,
            displayfig = false,
        ),
        log = timelogger(; nupdate = 100),
    ),
);

[ Info: t = 0.0948836	Δt = 0.001	umax = 3.4	itertime = 0.033
[ Info: t = 0.199428	Δt = 0.001	umax = 3.4	itertime = 0.01
[ Info: t = 0.318019	Δt = 0.0012	umax = 2.8	itertime = 0.0092
[ Info: t = 0.442745	Δt = 0.0013	umax = 2.8	itertime = 0.0095
[ Info: t = 0.573185	Δt = 0.0015	umax = 2.3	itertime = 0.0091
[ Info: t = 0.718973	Δt = 0.0015	umax = 2.3	itertime = 0.0091
[ Info: t = 0.874358	Δt = 0.0017	umax = 2.1	itertime = 0.0093
[ Info: Finished after 776 time steps and 9.7 seconds

Post-process

We may visualize or export the computed fields

Energy history

outputs.ehist

Energy spectrum

outputs.espec

Plot field

fieldplot(state; setup)

Copy-pasteable code

Below is the full code for this example stripped of comments and output.

using WGLMakie
using IncompressibleNavierStokes
# using CUDA

n = 256
ax = LinRange(0.0, 1.0, n + 1)
setup = Setup(;
    x = (ax, ax),
    boundary_conditions = (;
        u = ((PeriodicBC(), PeriodicBC()), (PeriodicBC(), PeriodicBC())),
    ),
    # backend = CUDABackend(),
)
u = random_field(setup, 0.0);

state, outputs = solve_unsteady(;
    setup,
    start = (; u),
    tlims = (0.0, 1.0),
    params = (; viscosity = 2.5e-4),
    processors = (
        rtp = realtimeplotter(; setup, nupdate = 10),
        ehist = realtimeplotter(;
            setup,
            plot = energy_history_plot,
            nupdate = 10,
            displayfig = false,
        ),
        espec = realtimeplotter(;
            setup,
            plot = energy_spectrum_plot,
            nupdate = 10,
            displayfig = false,
        ),
        log = timelogger(; nupdate = 100),
    ),
);

outputs.ehist

outputs.espec

fieldplot(state; setup)

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