Stratified Couette flow verification (CliMA#381)

Stratified Couette flow verification

Former-commit-id: 211e18c

Author: ali-ramadhan

test/runtests.jl

@@ -65,4 +65,5 @@ EquationsOfState = (LinearEquationOfState, RoquetIdealizedNonlinearEquationOfSta
     include("test_output_writers.jl")
     include("test_regression.jl")
     include("test_examples.jl")
+    include("test_verification.jl")
 end

test/test_verification.jl

@@ -0,0 +1,28 @@
+VERIFICATION_DIR = "../verification/"
+EXPERIMENTS = ["stratified_couette_flow"]
+
+for exp in EXPERIMENTS
+    script_filepath = joinpath(VERIFICATION_DIR, exp, exp * ".jl")
+    try
+        include(script_filepath)
+    catch err
+        @error sprint(showerror, err)
+    end
+end
+
+function run_stratified_couette_flow_verification(arch)
+    simulate_stratified_couette_flow(Nxy=16, Nz=8, arch=arch, Ri=0.01, Ni=1, end_time=1e-15)
+    return true
+end
+
+
+@testset "Verification" begin
+    println("Testing verification scripts...")
+
+    for arch in archs
+        @testset "Stratified Couette flow verification [$(typeof(arch))]" begin
+            println("  Testing stratified Couette flow verification [$(typeof(arch))]")
+            @test run_stratified_couette_flow_verification(arch)
+        end
+    end
+end

verification/stratified_couette_flow/run_stratified_couette_flow_simulations.jl

@@ -0,0 +1,6 @@
+include("stratified_couette_flow.jl")
+
+simulate_stratified_couette_flow(Nxy=128, Nz=128, Ri=0)
+simulate_stratified_couette_flow(Nxy=128, Nz=128, Ri=0.01)
+simulate_stratified_couette_flow(Nxy=128, Nz=128, Ri=0.04)
+

verification/stratified_couette_flow/stratified_couette_flow.jl

@@ -0,0 +1,260 @@
+using Statistics, Printf
+
+using Oceananigans
+using Oceananigans.TurbulenceClosures
+
+""" Friction velocity. See equation (16) of Vreugdenhil & Taylor (2018). """
+function uτ(model, Uavg)
+    Nz, Hz, Δz = model.grid.Nz, model.grid.Hz, model.grid.Δz
+    U_wall = model.parameters.U_wall
+    ν = model.closure.ν
+
+    U = Uavg(model)[1+Hz:end-Hz]  # Exclude average of halo region.
+
+    # Use a finite difference to calculate dU/dz at the top and bottomtom walls.
+    # The distance between the center of the cell adjacent to the wall and the
+    # wall itself is Δz/2.
+    uτ²_top    = ν * abs(U[1] - U_wall)    / (Δz/2)  # Top wall    where u = +U_wall
+    uτ²_bottom = ν * abs(-U_wall  - U[Nz]) / (Δz/2)  # Bottom wall where u = -U_wall
+
+    uτ_top, uτ_bottom = √uτ²_top, √uτ²_bottom
+
+    return uτ_top, uτ_bottom
+end
+
+""" Heat flux at the wall. See equation (16) of Vreugdenhil & Taylor (2018). """
+function q_wall(model, Tavg)
+    Nz, Hz, Δz = model.grid.Nz, model.grid.Hz, model.grid.Δz
+    Θ_wall = model.parameters.Θ_wall
+    κ = model.closure.κ
+
+    Θ = Tavg(model)[1+Hz:end-Hz]  # Exclude average of halo region.
+
+    # Use a finite difference to calculate dθ/dz at the top and bottomtom walls.
+    # The distance between the center of the cell adjacent to the wall and the
+    # wall itself is Δz/2.
+    q_wall_top    = κ * abs(Θ[1] - Θ_wall)   / (Δz/2)  # Top wall    where Θ = +Θ_wall
+    q_wall_bottom = κ * abs(-Θ_wall - Θ[Nz]) / (Δz/2)  # Bottom wall where Θ = -Θ_wall
+
+    return q_wall_top, q_wall_bottom
+end
+
+struct FrictionReynoldsNumber{H}
+    Uavg :: H
+end
+
+struct NusseltNumber{H}
+    Tavg :: H
+end
+
+""" Friction Reynolds number. See equation (20) of Vreugdenhil & Taylor (2018). """
+function (Reτ::FrictionReynoldsNumber)(model)
+    ν = model.closure.ν
+    h = model.grid.Lz / 2
+    uτ_top, uτ_bottom = uτ(model, Reτ.Uavg)
+
+    return h * uτ_top / ν, h * uτ_bottom / ν
+end
+
+""" Nusselt number. See equation (20) of Vreugdenhil & Taylor (2018). """
+function (Nu::NusseltNumber)(model)
+    κ = model.closure.κ
+    h = model.grid.Lz / 2
+    Θ_wall = model.parameters.Θ_wall
+
+    q_wall_top, q_wall_bottom = q_wall(model, Nu.Tavg)
+
+    return (q_wall_top * h)/(κ * Θ_wall), (q_wall_bottom * h)/(κ * Θ_wall)
+end
+
+"""
+    simulate_stratified_couette_flow(; Nxy, Nz, h=1, U_wall=1, Re=4250, Pr=0.7, Ri, Ni=10, end_time=1000)
+
+Simulate stratified plane Couette flow with `Nxy` grid cells in each horizontal
+direction, `Nz` grid cells in the vertical, in a domain of size (4πh, 2πh, 2h),
+with wall velocities of `U_wall` at the top and -`U_wall` at the bottom, at a Reynolds
+number `Re, Prandtl number `Pr`, and Richardson number `Ri`.
+
+`Ni` is the number of "intermediate" time steps taken at a time before printing a progress
+statement and updating the time step.
+"""
+function simulate_stratified_couette_flow(; Nxy, Nz, arch=GPU(), h=1, U_wall=1, Re=4250, Pr=0.7, Ri, Ni=10, end_time=1000)
+    ####
+    #### Computed parameters
+    ####
+
+         ν = U_wall * h / Re    # From Re = U_wall h / ν
+    Θ_wall = Ri * U_wall^2 / h  # From Ri = L Θ_wall / U_wall²
+         κ = ν / Pr             # From Pr = ν / κ
+
+    parameters = (U_wall=U_wall, Θ_wall=Θ_wall, Re=Re, Pr=Pr, Ri=Ri)
+
+    ####
+    #### Impose boundary conditions
+    ####
+
+    Tbcs = HorizontallyPeriodicBCs(    top = BoundaryCondition(Value,  Θ_wall),
+                                    bottom = BoundaryCondition(Value, -Θ_wall))
+
+    ubcs = HorizontallyPeriodicBCs(    top = BoundaryCondition(Value,  U_wall),
+                                    bottom = BoundaryCondition(Value, -U_wall))
+
+    vbcs = HorizontallyPeriodicBCs(    top = BoundaryCondition(Value, 0),
+                                    bottom = BoundaryCondition(Value, 0))
+
+    ####
+    #### Non-dimensional model setup
+    ####
+
+    model = Model(
+       architecture = arch,
+               grid = RegularCartesianGrid(N = (Nxy, Nxy, Nz), L = (4π*h, 2π*h, 2h)),
+           buoyancy = SeawaterBuoyancy(equation_of_state=LinearEquationOfState(α=1.0, β=0.0)),
+            closure = AnisotropicMinimumDissipation(ν=ν, κ=κ),
+boundary_conditions = HorizontallyPeriodicSolutionBCs(u=ubcs, v=vbcs, T=Tbcs),
+         parameters = parameters
+    )
+
+    ####
+    #### Set initial conditions
+    ####
+
+    # Add a bit of surface-concentrated noise to the initial condition
+    ε(σ, z) = σ * randn() * z/model.grid.Lz * (1 + z/model.grid.Lz)
+
+    # We add a sinusoidal initial condition to u to encourage instability.
+    T₀(x, y, z) = 2Θ_wall * (1/2 + z/model.grid.Lz) * (1 + ε(5e-1, z))
+    u₀(x, y, z) = 2U_wall * (1/2 + z/model.grid.Lz) * (1 + ε(5e-1, z)) * (1 + 0.5*sin(4π/model.grid.Lx * x))
+    v₀(x, y, z) = ε(5e-1, z)
+    w₀(x, y, z) = ε(5e-1, z)
+
+    set_ic!(model, u=u₀, v=v₀, w=w₀, T=T₀)
+
+    ####
+    #### Print simulation banner
+    ####
+
+    @printf(
+        """
+        Simulating stratified plane Couette flow
+
+                N : %d, %d, %d
+                L : %.3g, %.3g, %.3g
+               Re : %.3f
+               Ri : %.3f
+               Pr : %.3f
+                ν : %.3g
+                κ : %.3g
+           U_wall : %.3f
+           Θ_wall : %.3f
+
+        """, model.grid.Nx, model.grid.Ny, model.grid.Nz,
+             model.grid.Lx, model.grid.Ly, model.grid.Lz,
+             Re, Ri, Pr, ν, κ, U_wall, Θ_wall)
+
+    ####
+    #### Set up field output writer
+    ####
+
+    base_dir = @sprintf("stratified_couette_flow_data_Nxy%d_Nz%d_Ri%.2f", Nxy, Nz, Ri)
+    prefix = @sprintf("stratified_couette_flow_Nxy%d_Nz%d_Ri%.2f", Nxy, Nz, Ri)
+
+    function init_save_parameters_and_bcs(file, model)
+        file["parameters/reynolds_number"] = Re
+        file["parameters/richardson_number"] = Ri
+        file["parameters/prandtl_number"] = Pr
+        file["parameters/viscosity"] = ν
+        file["parameters/diffusivity"] = κ
+        file["parameters/wall_velocity"] = U_wall
+        file["parameters/wall_temperature"] = Θ_wall
+    end
+
+    fields = Dict(
+        :u => model -> Array(model.velocities.u.data.parent),
+        :v => model -> Array(model.velocities.v.data.parent),
+        :w => model -> Array(model.velocities.w.data.parent),
+        :T => model -> Array(model.tracers.T.data.parent),
+   :kappaT => model -> Array(model.diffusivities.κₑ.T.data.parent),
+       :nu => model -> Array(model.diffusivities.νₑ.data.parent))
+
+    field_writer = JLD2OutputWriter(model, fields; dir=base_dir, prefix=prefix * "_fields",
+                                    init=init_save_parameters_and_bcs,
+                                    interval=10, force=true, verbose=true)
+
+    push!(model.output_writers, field_writer)
+
+    ####
+    #### Set up profile output writer
+    ####
+
+    Uavg = HorizontalAverage(model, model.velocities.u;       return_type=Array)
+    Vavg = HorizontalAverage(model, model.velocities.v;       return_type=Array)
+    Wavg = HorizontalAverage(model, model.velocities.w;       return_type=Array)
+    Tavg = HorizontalAverage(model, model.tracers.T;          return_type=Array)
+    νavg = HorizontalAverage(model, model.diffusivities.νₑ;   return_type=Array)
+    κavg = HorizontalAverage(model, model.diffusivities.κₑ.T; return_type=Array)
+
+    profiles = Dict(
+         :u => model -> Uavg(model),
+         :v => model -> Vavg(model),
+         :w => model -> Wavg(model),
+         :T => model -> Tavg(model),
+        :nu => model -> νavg(model),
+    :kappaT => model -> κavg(model))
+
+    profile_writer = JLD2OutputWriter(model, profiles; dir=base_dir, prefix=prefix * "_profiles",
+                                      init=init_save_parameters_and_bcs, interval=1, force=true, verbose=true)
+
+    push!(model.output_writers, profile_writer)
+
+    ####
+    #### Set up statistic output writer
+    ####
+
+    Reτ = FrictionReynoldsNumber(Uavg)
+     Nu = NusseltNumber(Tavg)
+
+    statistics = Dict(
+        :Re_tau => model -> Reτ(model),
+        :Nu     => model -> Nu(model))
+
+    statistics_writer = JLD2OutputWriter(model, statistics; dir=base_dir, prefix=prefix * "_statistics",
+                                     init=init_save_parameters_and_bcs, interval=1/2, force=true, verbose=true)
+
+    push!(model.output_writers, statistics_writer)
+
+    ####
+    #### Time stepping
+    ####
+
+    wizard = TimeStepWizard(cfl=0.02, Δt=0.0001, max_change=1.1, max_Δt=0.02)
+
+    cfl(t) = min(0.01*t, 0.1)
+
+    while model.clock.time < end_time
+        wizard.cfl = cfl(model.clock.time)
+
+        walltime = @elapsed time_step!(model; Nt=Ni, Δt=wizard.Δt)
+        progress = 100 * (model.clock.time / end_time)
+
+        umax = maximum(abs, model.velocities.u.data.parent)
+        vmax = maximum(abs, model.velocities.v.data.parent)
+        wmax = maximum(abs, model.velocities.w.data.parent)
+        CFL = wizard.Δt / Oceananigans.cell_advection_timescale(model)
+
+        νmax = maximum(model.diffusivities.νₑ.data.parent)
+        κmax = maximum(model.diffusivities.κₑ.T.data.parent)
+
+        Δ = min(model.grid.Δx, model.grid.Δy, model.grid.Δz)
+        νCFL = wizard.Δt / (Δ^2 / νmax)
+        κCFL = wizard.Δt / (Δ^2 / κmax)
+
+        update_Δt!(wizard, model)
+
+        @printf("[%06.2f%%] i: %d, t: %4.2f, umax: (%6.3g, %6.3g, %6.3g) m/s, CFL: %6.4g, νκmax: (%6.3g, %6.3g), νκCFL: (%6.4g, %6.4g), next Δt: %8.5g, ⟨wall time⟩: %s\n",
+                progress, model.clock.iteration, model.clock.time,
+                umax, vmax, wmax, CFL, νmax, κmax, νCFL, κCFL,
+                wizard.Δt, prettytime(walltime / Ni))
+    end
+end
+