(5) Run Simulation
FLOWUnsteady.run_simulation — FunctionRun the FLOWUnsteady simulation sim in nsteps number of time steps.
run_simulation(
sim::Simulation, # Simulation object
nsteps::Int; # Total time steps in simulation
# -------- SIMULATION OPTIONS -----------------------------------------
Vinf = (X, t)->zeros(3), # Freestream velocity
sound_spd = 343, # (m/s) speed of sound
rho = 1.225, # (kg/m^3) air density
mu = 1.81e-5, # (Pa*s) air dynamic viscosity
tquit = Inf, # (s) force quit the simulation at this time
rand_RPM = false, # (experimental) randomize RPM fluctuations
extra_runtime_function = (sim, PFIELD, T, DT; optargs...)->false,
# -------- SOLVERS OPTIONS --------------------------------------------
# Vortex particle method
max_particles = Int(1e5), # Maximum number of particles
max_static_particles = nothing, # Maximum number of static particles (use `nothing` to automatically estimate it)
p_per_step = 1, # Particle sheds per time step
vpm_formulation = vpm.rVPM, # VPM formulation (`vpm.rVPM` or `vpm.cVPM`)
vpm_kernel = vpm.gaussianerf, # VPM kernel (`vpm.gaussianerf` or `vpm.winckelmans`)
vpm_UJ = vpm.UJ_fmm, # VPM particle-to-particle interaction scheme (`vpm.UJ_fmm` or `vpm.UJ_direct`)
vpm_SFS = vpm.SFS_none, # VPM LES subfilter-scale model (`SFS_none`, `SFS_Cd_threelevel_nobackscatter`, `SFS_Cd_twolevel_nobackscatter`, or `SFS_Cs_nobackscatter`)
vpm_integration = vpm.rungekutta3, # VPM time integration scheme (`vpm.euler` or `vpm.rungekutta3`)
vpm_transposed = true, # VPM transposed stretching scheme
vpm_viscous = vpm.Inviscid(), # VPM viscous diffusion scheme (`vpm.Inviscid()`, `vpm.CoreSpreading(nu, sgm0, zeta)`, or `vpm.ParticleStrengthExchange(nu)`)
vpm_fmm = vpm.FMM(; p=4, ncrit=50, theta=0.4, phi=0.5), # VPM's FMM settings
vpm_relaxation = vpm.pedrizzetti, # VPM relaxation scheme (`vpm.norelaxation`, `vpm.correctedpedrizzetti`, or `vpm.pedrizzetti`)
vpm_surface = true, # Whether to include surfaces in the VPM through ASM/ALM
# Actuator surface/line model (ASM/ALM): VLM and blade elements
vlm_vortexsheet = false, # Whether to spread surface circulation as a vortex sheet in the VPM (turns ASM on; ALM if false)
vlm_vortexsheet_overlap = 2.125,# Overlap of particles that make the vortex sheet
vlm_vortexsheet_distribution= g_pressure, # Vorticity distribution of vortex sheet (`g_uniform`, `g_linear`, or `g_pressure`)
vlm_vortexsheet_sigma_tbv = nothing, # Size of particles in trailing bound vortices (defaults to `sigma_vlm_surf` if not given)
vlm_rlx = -1, # VLM relaxation (>0.9 can cause divergence, <0.2 slows simulation too much, deactivated with <0)
vlm_init = false, # Initialize the first step with the VLM semi-infinite wake solution
hubtiploss_correction = vlm.hubtiploss_nocorrection, # Hub and tip loss correction of rotors (ignored in quasi-steady solver)
# Wake shedding
wake_coupled = true, # Couple VPM wake -> VLM solution
shed_unsteady = true, # Whether to shed vorticity from unsteady loading
unsteady_shedcrit = 0.01, # Criterion for unsteady-loading shedding
shed_starting = false, # Whether to shed starting vortex (only when `shed_unsteady=true`)
shed_boundarylayer = false, # (experimental) whether to shed vorticity from boundary layer of surfaces
boundarylayer_prescribedCd = 0.1, # (experimental) prescribed Cd for boundary layer shedding used for wings
boundarylayer_d = 0.0, # (experimental) dipole width for boundary layer shedding
omit_shedding = [], # Indices of elements in `sim.vehicle.wake_system` on which omit shedding VPM particles
# Regularization of solvers
sigma_vlm_solver = -1, # Regularization of VLM solver (internal VLM-on-VLM)
sigma_vlm_surf = -1, # (REQUIRED!) Size of embedded particles in ASM/ALM wing surfaces (for VLM-on-VPM and VLM-on-Rotor)
sigma_rotor_surf = -1, # (REQUIRED!) Size of embedded particles in ALM blade surfaces (for Rotor-on-VPM, Rotor-on-VLM, and Rotor-on-Rotor)
sigmafactor_vpm = 1.0, # Core overlap of wake particles
sigmafactor_vpmonvlm = 1, # (experimental) shrinks the particles by this factor when calculating VPM-on-VLM/Rotor induced velocities
sigma_vpm_overwrite = nothing, # Overwrite core size of wake to this value (ignoring `sigmafactor_vpm`)
# -------- RESTART OPTIONS --------------------------------------------
restart_vpmfile = nothing, # VPM restart file to restart simulation
# -------- OUTPUT OPTIONS ---------------------------------------------
save_path = nothing, # Where to save simulation
run_name = "flowunsteadysim",# Suffix of output files
create_savepath = true, # Whether to create `save_path`
prompt = true, # Whether to prompt the user
verbose = true, # Enable verbose
v_lvl = 0, # Indentation level of verbose
verbose_nsteps = 10, # Verbose every this many steps
raisewarnings = true, # Whether to raise warnings
debug = false, # Output extra states for debugging
nsteps_save = 1, # Save vtks every this many steps
nsteps_restart = -1, # Save jlds every this many steps (restart files)
save_code = "", # Copy the source code in this path to `save_path`
save_horseshoes = false, # Whether to output VLM horseshoes in VTKs
save_static_particles = true, # Whether to save ASM/ALM embedded particles
save_wopwopin = false, # Generate input files for PSU-WOPWOP
)Even though a bast number of settings are exposed to the user, the only required keyword arguments are sigma_vlm_surf and sigma_rotor_surf. Thus, running the simulation can be as simple as
run_simulation(sim::Simulation, nsteps::Int;
sigma_vlm_surf = ..., sigma_rotor_surf = ...)extra_runtime_function is a function that is called at every time step after the state variables are updated and before outputting VTK files. The state variables of the simulation are passed to this function, giving the user complete freedom to modify the states of the simulation (e.g., add/remove particles, clip vortex strengths, re-orient the vehicle) or to do some extra computation (e.g., compute aerodynamic forces, create plots, write to files, etc).
This function is expected be of the form
extra_runtime_function(sim, pfield, t, dt; vprintln) -> Boolwhere sim is the FLOWUnsteady.Simulation object, pfield is the FLOWVPM.ParticleField, t is the current simulation time, dt is the length of the current time step, and vprintln(str, v_lvl) is a function for printing the verbose of the simulation (default to vprintln = (args...)->nothing if there is nothing to add to the verbose).
The output of extra_runtime_function is a flag for breaking the simulation at the current time step, such that if it ever returns true, the simulation will immediately quit.
FLOWUnsteady is simply a runtime function that is provided to FLOWVPM, as shown below. Hence, FLOWVPM (green block) is the solver that is actually driving the simulation. FLOWUnsteady (blue block) acts as a runtime function inside a VPM simulation that at each time step uses the solvers in the gray block to compute surface vorticities and adds particles to embed such vorticity in the flow field (thus implementing the actuator surface/line models developed in Alvarez' dissertation, Chapter 6).
This workflow makes it very easy to couple more solvers in the simulation. For instance, a structural solver can be inserted as a runtime function (step 6 of the blue block) that deflects the geometry according to the aerodynamic loads, obtaining a full aeroelastic simulation.
