Error with the Run of FAST.Farm on a model Turbine with ModWake 2 (Curl)

[LucaFFPo]

Good Morning, I am trying to run a simulation of a Model of the 10MW DTU RWT with a scale of the lengths of 150, so the final dimension of the rotor is 1.2 m.
The simulation is composed of 3 turbines in series placed at 4.5D of distance between each other and at the first turbine is imposed a yaw step thorugh an external platform. In ElastoDyn are allowed only FlapDOF1 and FlapDOF2 (and the PltfYaw for the first Turbine) with a DT in ElastoDyn of 0.0002s.
Simulations are running with a ModWake 1 (Polar), while by using the ModWake 2 (Curl) depending on the turbulent wind generated, some are completed while some other are not. In those completed the Thrust on the second Turbine is lower than the case of ModWake1, and by searching online I saw that the variable k_vCurl has to be tuned, in particular I need to increase it to allow a faster wake recovery and so increase the Thrust of the Turbine in the wake.

Bug description
By increasing k_vCurl from DEFAULT (2) to 2.3 i get the following error:

The BEM solution is being turned off due to low TSR. (TSR = -1.13785E-07). This warning will not
be repeated though the condition may persist. (See GeomPhi output channel.)
The BEM solution is being turned off due to low TSR. (TSR = -1.34628E-08). This warning will not
be repeated though the condition may persist. (See GeomPhi output channel.)

T1:FARM_UpdateStates:FWrap_Increment:FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:In
flowWind_CalcOutput:CalculateOutput:IfW_FlowField_GetVelAcc:Grid4DField_GetVel:Outside the grid
bounds.
InflowWind_CalcOutput:InflowWind_GetSpatialAverage:CalculateOutput:IfW_FlowField_GetVelAcc:Grid4DF
ield_GetVel:Outside the grid bounds.
InflowWind_CalcOutput:InflowWind_GetHubValues:CalculateOutput:IfW_FlowField_GetVelAcc:Grid4DField_
GetVel:Outside the grid bounds.
T3:FARM_UpdateStates:FWrap_Increment:FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_AB4:ED_CalcContSt
ateDeriv:SetCoordSy:Small angle assumption violated in SUBROUTINE SmllRotTrans() due to a large
blade deflection (ElastoDyn SetCoordSy). The solution may be inaccurate. Simulation continuing,
but future warnings from SmllRotTrans() will be suppressed.
Additional debugging message from SUBROUTINE SmllRotTrans(): 2.3502 s
FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalculateOutput:IfW_FlowField_G
etVelAcc:Grid4DField_GetVel:Outside th

FAST Input file

--- SIMULATION CONTROL ---
False Echo Echo input data to .ech? (flag)
FATAL AbortLevel Error level when simulation should abort (string) {"WARNING", "SEVERE", "FATAL"}
96 TMax Total run time (s) [>=0.0]
False UseSC Use a super controller? (flag)
2 Mod_AmbWind Ambient wind model (-) (switch) {1: high-fidelity precursor in VTK format, 2: one InflowWind module, 3: multiple instances of InflowWind module}
2 Mod_WaveField Wave field handling (-) (switch) {1: use individual HydroDyn inputs without adjustment, 2: adjust wave phases based on turbine offsets from farm origin}
0 Mod_SharedMooring Shared mooring system model (switch) {0: None, 3=MoorDyn}}
--- SUPER CONTROLLER --- [used only for UseSC=True]
"SC_DLL.dll" SC_FileName Name/location of the dynamic library {.dll [Windows] or .so [Linux]} containing the Super Controller algorithms (quoated string)
--- SHARED MOORING SYSTEM --- [used only for Mod_SharedMoor>0]
"" SharedMoorFile Name of file containing shared mooring system input parameters (quoted string) [used only when Mod_SharedMooring > 0]
0.005 DT_Mooring Time step for farm-level mooring coupling with each turbine (s) [used only when Mod_SharedMooring > 0]
--- AMBIENT WIND: PRECURSOR IN VTK FORMAT --- [used only for Mod_AmbWind=1]
2.0 DT_Low-VTK Time step for low -resolution wind data input files ; will be used as the global FAST.Farm time step (s) [>0.0]
0.5 DT_High-VTK Time step for high-resolution wind data input files (s) [>0.0]
"unused" WindFilePath Path name to VTK wind data files from precursor (string)
False ChkWndFiles Check all the ambient wind files for data consistency? (flag)
--- AMBIENT WIND: INFLOWWIND MODULE --- [used only for Mod_AmbWind=2 or 3]
0.06 DT_Low Time step for low -resolution wind data interpolation; will be used as the global FAST.Farm time step (s) [>0.0]
0.03 DT_High Time step for high-resolution wind data interpolation (s) [>0.0]
176 NX_Low Number of low -resolution spatial nodes in X direction for wind data interpolation (-) [>=2]
26 NY_Low Number of low -resolution spatial nodes in Y direction for wind data interpolation (-) [>=2]
24 NZ_Low Number of low -resolution spatial nodes in Z direction for wind data interpolation (-) [>=2]
0 X0_Low Origin of low -resolution spatial nodes in X direction for wind data interpolation (m)
-1.5500 Y0_Low Origin of low -resolution spatial nodes in Y direction for wind data interpolation (m)
0.0556 Z0_Low Origin of low -resolution spatial nodes in Z direction for wind data interpolation (m)
0.1240 dX_Low Spacing of low -resolution spatial nodes in X direction for wind data interpolation (m) [>0.0]
0.1240 dY_Low Spacing of low -resolution spatial nodes in Y direction for wind data interpolation (m) [>0.0]
0.1240 dZ_Low Spacing of low -resolution spatial nodes in Z direction for wind data interpolation (m) [>0.0]
25 NX_High Number of high-resolution spatial nodes in X direction for wind data interpolation (-) [>=2]
25 NY_High Number of high-resolution spatial nodes in Y direction for wind data interpolation (-) [>=2]
26 NZ_High Number of high-resolution spatial nodes in Z direction for wind data interpolation (-) [>=2]
"...\InflowWind.dat" InflowFile Name of file containing InflowWind module input parameters (quoted string)
--- WIND TURBINES ---
3 NumTurbines Number of wind turbines (-) [>=1] [last 6 columns below used only for Mod_AmbWind=2 or 3]
WT_X WT_Y WT_Z WT_FASTInFile X0_High Y0_High Z0_High dX_High dY_High dZ_High
(m) (m) (m) (string) (m) (m) (m) (m) (m) (m)
2.496 0.0 0.0 "...\WTM12A_T1.fst" 1.752 -0.744 0.0556 0.0620 0.0620 0.0620
7.896 0.0 0.0 "...\WTM12A_T2.fst" 7.152 -0.744 0.0556 0.0620 0.0620 0.0620
13.296 0.0 0.0 "...\WTM12A_T3.fst" 12.552 -0.744 0.0556 0.0620 0.0620 0.0620
--- WAKE DYNAMICS ---
2 Mod_Wake - Switch between wake formulations {1:Polar, 2:Curl, 3:Cartesian} (-) (switch)
0.062 dr Radial increment of radial finite-difference grid (m) [>0.0]
39 NumRadii Number of radii in the radial finite-difference grid (-) [>=2]
96 NumPlanes Number of wake planes (-) [>=2]
DEFAULT f_c Cutoff (corner) frequency of the low-pass time-filter for the wake advection, deflection, and meandering model (Hz) [>0.0] or DEFAULT [DEFAULT=0.0007]
DEFAULT C_HWkDfl_O Calibrated parameter in the correction for wake deflection defining the horizontal offset at the rotor (m ) or DEFAULT [DEFAULT= 0.0 ]
0.0 C_HWkDfl_OY Calibrated parameter in the correction for wake deflection defining the horizontal offset at the rotor scaled with yaw error (m/deg) or DEFAULT [DEFAULT= 0.3 ]
DEFAULT C_HWkDfl_x Calibrated parameter in the correction for wake deflection defining the horizontal offset scaled with downstream distance (- ) or DEFAULT [DEFAULT= 0.0 ]
DEFAULT C_HWkDfl_xY Calibrated parameter in the correction for wake deflection defining the horizontal offset scaled with downstream distance and yaw error (1/deg) or DEFAULT [DEFAULT=-0.004]
DEFAULT C_NearWake Calibrated parameter for the near-wake correction (-) [>1.0 and <2.5] or DEFAULT [DEFAULT=1.8]
DEFAULT k_vAmb Calibrated parameter for the influence of ambient turbulence in the eddy viscosity (-) [>=0.0] or DEFAULT [DEFAULT=0.05 ]
DEFAULT k_vShr Calibrated parameter for the influence of the shear layer in the eddy viscosity (-) [>=0.0] or DEFAULT [DEFAULT=0.016]
DEFAULT C_vAmb_DMin Calibrated parameter in the eddy viscosity filter function for ambient turbulence defining the transitional diameter fraction between the minimum and exponential regions (-) [>=0.0 ] or DEFAULT [DEFAULT= 0.0 ]
DEFAULT C_vAmb_DMax Calibrated parameter in the eddy viscosity filter function for ambient turbulence defining the transitional diameter fraction between the exponential and maximum regions (-) [> C_vAmb_DMin ] or DEFAULT [DEFAULT= 1.0 ]
DEFAULT C_vAmb_FMin Calibrated parameter in the eddy viscosity filter function for ambient turbulence defining the value in the minimum region (-) [>=0.0 and <=1.0] or DEFAULT [DEFAULT= 1.0 ]
DEFAULT C_vAmb_Exp Calibrated parameter in the eddy viscosity filter function for ambient turbulence defining the exponent in the exponential region (-) [> 0.0 ] or DEFAULT [DEFAULT= 0.01]
DEFAULT C_vShr_DMin Calibrated parameter in the eddy viscosity filter function for the shear layer defining the transitional diameter fraction between the minimum and exponential regions (-) [>=0.0 ] or DEFAULT [DEFAULT= 3.0 ]
DEFAULT C_vShr_DMax Calibrated parameter in the eddy viscosity filter function for the shear layer defining the transitional diameter fraction between the exponential and maximum regions (-) [> C_vShr_DMin ] or DEFAULT [DEFAULT=25.0 ]
DEFAULT C_vShr_FMin Calibrated parameter in the eddy viscosity filter function for the shear layer defining the value in the minimum region (-) [>=0.0 and <=1.0] or DEFAULT [DEFAULT= 0.2 ]
DEFAULT C_vShr_Exp Calibrated parameter in the eddy viscosity filter function for the shear layer defining the exponent in the exponential region (-) [> 0.0 ] or DEFAULT [DEFAULT= 0.1 ]
DEFAULT Mod_WakeDiam Wake diameter calculation model (-) (switch) {1: rotor diameter, 2: velocity based, 3: mass-flux based, 4: momentum-flux based} or DEFAULT [DEFAULT=1]
DEFAULT C_WakeDiam Calibrated parameter for wake diameter calculation (-) [>0.0 and <0.99] or DEFAULT [DEFAULT=0.95] [unused for Mod_WakeDiam=1]
DEFAULT Mod_Meander Spatial filter model for wake meandering (-) (switch) {1: uniform, 2: truncated jinc, 3: windowed jinc} or DEFAULT [DEFAULT=3]
DEFAULT C_Meander Calibrated parameter for wake meandering (-) [>=1.0] or DEFAULT [DEFAULT=1.9]
--- CURLED-WAKE PARAMETERS [only used if Mod_Wake=2 or 3] ---
True Swirl - Switch to include swirl velocities in wake [only used if Mod_Wake=2 or Mod_Wake=3] (-) (switch) [DEFAULT=TRUE]
0 k_VortexDecay - Vortex decay constant for curl (-) [DEFAULT=0]
DEFAULT NumVortices - The number of vortices in the curled wake model (-) [DEFAULT=100]
DEFAULT sigma_D - The width of the vortices in the curled wake model non-dimesionalized by rotor diameter (-) [DEFAULT=0.2]
DEFAULT FilterInit - Switch to filter the initial wake plane deficit and select the number of grid points for the filter {0: no filter, 1: filter of size 1} or DEFAULT [DEFAULT=1] [unused for Mod_Wake=1] (switch)
2.7 k_vCurl - Calibrated parameter for scaling the eddy viscosity in the curled-wake model (-) [only used if Mod_Wake=2 or Mod_Wake=3] [>=0] or DEFAULT [DEFAULT=2.0 ]
DEFAULT Mod_Projection - Switch to select how the wake plane velocity is projected in AWAE {1: keep all components, 2: project against plane normal} or DEFAULT [DEFAULT=1: if Mod_Wake is 1 or 3, or DEFAULT=2: if Mod_Wake is 2] (switch)

Fast.FARM Version
FAST.Farm-v3.5.1
Compile Info:

• Compiler: Intel(R) Fortran Compiler 2021
• Architecture: 64 bit
• Precision: single
• OpenMP: Yes, number of threads: 8/8
• Date: Oct 21 2023
• Time: 09:22:40
  Execution Info:
• Date: 02/22/2024
• Time: 08:42:13+0100

I have a bit of trouble to find a way to solve this error. What could be the problem? Thank you :)

[jjonkman]

Dear @LucaFFPo,

It appears that there is a problem with the domain for T1, and that the OpenFAST model of T3 is going unstable.

What wind conditions are you simulating and what is the mean wind speed? Are you following the rules of thumb for DT_Low and DS_Low corrected in the following issue: #1822?

Have you visualized the flow field or output the wind velocities at each rotor; does anything stand out as incorrect in the wake?

Best regards,