Add simple SGS to Adami and Morris Viscosity

examples/fluid/dam_break_2d.jl

@@ -47,12 +47,21 @@ smoothing_length = 1.75 * fluid_particle_spacing
 smoothing_kernel = WendlandC2Kernel{2}()
 
 fluid_density_calculator = ContinuityDensity()
-viscosity = ArtificialViscosityMonaghan(alpha=0.02, beta=0.0)
-# nu = 0.02 * smoothing_length * sound_speed/8
-# viscosity = ViscosityMorris(nu=nu)
-# viscosity = ViscosityMorrisSGS(nu=nu)
+alpha = 0.02
+viscosity = ArtificialViscosityMonaghan(alpha=alpha, beta=0.0)
+# A typical formula to convert Artificial viscosity to a
+# kinematic viscosity is provided by Monaghan as
+# nu = alpha * smoothing_length * sound_speed/8
+
+# Alternatively a kinematic viscosity for water can be set
+# nu = 1.0e-6
+
+# This allows the use of a physical viscosity model like:
 # viscosity = ViscosityAdami(nu=nu)
+# or with additional dissipation through a Smagorinsky model
 # viscosity = ViscosityAdamiSGS(nu=nu)
+# For more details see the documentation [Viscosity model overview](@ref viscosity_sph).
+
 # Alternatively the density diffusion model by Molteni & Colagrossi can be used,
 # which will run faster.
 # density_diffusion = DensityDiffusionMolteniColagrossi(delta=0.1)

examples/fluid/taylor_green_vortex_2d.jl

@@ -79,7 +79,7 @@ if wcsph
                                                state_equation, smoothing_kernel,
                                                pressure_acceleration=TrixiParticles.inter_particle_averaged_pressure,
                                                smoothing_length,
-                                               viscosity=ViscosityAdamiSGS(; nu, C_S=0.2),
+                                               viscosity=ViscosityAdami(; nu),
                                                transport_velocity=TransportVelocityAdami(background_pressure))
 else
     density_calculator = SummationDensity()
@@ -100,7 +100,7 @@ ode = semidiscretize(semi, tspan)
 
 info_callback = InfoCallback(interval=100)
 
-saving_callback = SolutionSavingCallback(dt=0.02, prefix="SGS")
+saving_callback = SolutionSavingCallback(dt=0.02)
 
 pp_callback = nothing
 

src/schemes/fluid/viscosity.jl

@@ -177,8 +177,7 @@ struct ViscosityAdami{ELTYPE}
 end
 
 function adami_viscosity_force(smoothing_length_average, pos_diff, distance, grad_kernel,
-                               m_a,
-                               m_b, rho_a, rho_b, v_diff, nu_a, nu_b, epsilon)
+                               m_a, m_b, rho_a, rho_b, v_diff, nu_a, nu_b, epsilon)
     eta_a = nu_a * rho_a
     eta_b = nu_b * rho_b
 
@@ -241,8 +240,9 @@ end
 @doc raw"""
     ViscosityAdamiSGS(; nu, C_S=0.1, epsilon=0.01)
 
-Viscosity model that extends the standard Adami formulation by incorporating a subgrid-scale (SGS)
-eddy viscosity via a Smagorinsky-type closure. The effective kinematic viscosity is defined as
+Viscosity model that extends the standard [Adami formulation](@ref ViscosityAdami)
+by incorporating a subgrid-scale (SGS) eddy viscosity via a Smagorinsky-type closure.
+The effective kinematic viscosity is defined as
 
 ```math
 \nu_{\mathrm{eff}} = \nu_{\\mathrm{std}} + \nu_{\\mathrm{SGS}},
@@ -278,10 +278,10 @@ This model is appropriate for turbulent flows where unresolved scales contribute
 # Keywords
 - `nu`:      Standard kinematic viscosity.
 - `C_S`:     Smagorinsky constant.
-- `epsilon`: Epsilon for singularity prevention [e.g., 0.001]
+- `epsilon=0.01`: Parameter to prevent singularities
 """
 struct ViscosityAdamiSGS{ELTYPE}
-    nu::ELTYPE      # Standard (molecular) kinematic viscosity [e.g., 1e-6 m²/s]
+    nu::ELTYPE      # kinematic viscosity [e.g., 1e-6 m²/s]
     C_S::ELTYPE     # Smagorinsky constant [e.g., 0.1-0.2]
     epsilon::ELTYPE # Epsilon for singularity prevention [e.g., 0.001]
 end
@@ -379,10 +379,10 @@ This model is appropriate for turbulent flows where unresolved scales contribute
 # Keywords
 - `nu`:      Standard kinematic viscosity.
 - `C_S`:     Smagorinsky constant.
-- `epsilon`: Epsilon for singularity prevention [e.g., 0.001]
+- `epsilon=0.01`: Parameter to prevent singularities
 """
 struct ViscosityMorrisSGS{ELTYPE}
-    nu::ELTYPE      # Standard (molecular) kinematic viscosity [e.g., 1e-6 m²/s]
+    nu::ELTYPE      # kinematic viscosity [e.g., 1e-6 m²/s]
     C_S::ELTYPE     # Smagorinsky constant [e.g., 0.1-0.2]
     epsilon::ELTYPE # Epsilon for singularity prevention [e.g., 0.001]
 end

validation/taylor_green_vortex_2d/validation_taylor_green_vortex_2d.jl

@@ -2,7 +2,14 @@ using TrixiParticles
 
 # ==========================================================================================
 # ==== Resolution
+# P. Ramachandran, K. Puri
+# "Entropically damped artificial compressibility for SPH".
+# In: Computers and Fluids, Volume 179 (2019), pages 579-594.
+# https://doi.org/10.1016/j.compfluid.2018.11.023
+# The following resolutions are used in the paper:
 # particle_spacings = [0.02, 0.01, 0.005]
+
+# To save time only the configuration with 50x50 particles are used here.
 particle_spacings = [0.02]
 
 # ==========================================================================================