Actuator Turbine Model¶

actuator¶: actuator subsection defines the inputs for actuator line simulations. A sample section is shown below for running actuator line simulations coupled to OpenFAST with two turbines.

actuator:
  type: ActLineFAST
  search_method: stk_kdtree
  search_target_part: Unspecified-2-HEX

  n_turbines_glob: 2
  dry_run:  False
  debug:    False
  t_start: 0.0
  simStart: init # init/trueRestart/restartDriverInitFAST
  t_max:    5.0
  n_every_checkpoint: 100

  Turbine0:
    procNo: 0
    num_force_pts_blade: 50
    num_force_pts_tower: 20
    nacelle_cd: 1.0
    nacelle_area: 1.0
    air_density: 1.225
    epsilon: [ 5.0, 5.0, 5.0 ]
    turbine_base_pos: [ 0.0, 0.0, -90.0 ]
    turbine_hub_pos: [ 0.0, 0.0, 0.0 ]
    restart_filename: ""
    FAST_input_filename: "Test01.fst"
    turb_id:  1
    turbine_name: machine_zero

  Turbine1:
    procNo: 0
    num_force_pts_blade: 50
    num_force_pts_tower: 20
    nacelle_cd: 1.0
    nacelle_area: 1.0
    air_density: 1.225
    epsilon: [ 5.0, 5.0, 5.0 ]
    turbine_base_pos: [ 250.0, 0.0, -90.0 ]
    turbine_hub_pos: [ 250.0, 0.0, 0.0 ]
    restart_filename: ""
    FAST_input_filename: "Test02.fst"
    turb_id:  2
    turbine_name: machine_one

actuator.type¶: Type of actuator source. Options are ActLineFAST and ActDiskFAST. ActLineFAST is for actuator lines, and ActDiskFAST is for actuator disks. The actuator disk uses a stationary actuator line model to compute forces at the blade locations and then the average force of the blades is spread azimuthally between the blades sampling points.

actuator.search_method¶: String specifying the type of search method used to identify the nodes within the search radius of the actuator points. The only valid option is stk_kdtree. The boost_rtree option has been deprecated by the STK search library.

search_target_part¶: String or an array of strings specifying the parts of the mesh to be searched to identify the nodes near the actuator points.

actuator.n_turbines_glob¶: Total number of turbines in the simulation. The input file must contain a number of turbine specific sections (Turbine0, Turbine1, …, Turbine(n-1)) that is consistent with nTurbinesGlob.

actuator.debug¶: Enable debug outputs if set to true

actuator.dry_run¶: The simulation will not run if dryRun is set to true. However, the simulation will read the input files, allocate turbines to processors and prepare to run the individual turbine instances. This flag is useful to test the setup of the simulation before running it.

actuator.simStart¶

Flag indicating whether the simulation starts from scratch or restart. simStart takes on one of three values:

init - Use this option when starting a simulation from t=0s.
trueRestart - While OpenFAST allows for restart of a turbine simulation, external components like the Bladed style controller may not. Use this option when all components of the simulation are known to restart.
restartDriverInitFAST - When the restartDriverInitFAST option is selected, the individual turbine models start from t=0s and run up to the specified restart time using the inflow data stored at the actuator nodes from a hdf5 file. The C++ API stores the inflow data at the actuator nodes in a hdf5 file at every OpenFAST time step and then reads it back when using this restart option. This restart option is especially useful when the glue code is a CFD solver.

actuator.t_start¶: Start time of the simulation

actuator.t_end¶: End time of the simulation. t_end <= t_max

actuator.t_max¶: Max time of the simulation

Note

t_max can only be set when OpenFAST is running from t=0s and simStart is init. t_max can not be changed on a restart. OpenFAST will not be able to run beyond t_max. Choose t_max to be large enough to accomodate any possible future extensions of runs. One can change t_start and t_end to start and stop the simulation any number of times as long as t_end <= t_max.

actuator.dt_fast¶: Time step for OpenFAST. All turbines should have the same time step.

actuator.n_every_checkpoint¶: Restart files will be written every so many time steps

Turbine specific input options

actuator.turbine_base_pos¶: The position of the turbine base for actuator-line/disk simulations

actuator.num_force_pts_blade¶: The number of actuator points along each blade for actuator-line/disk simulations

actuator.num_force_pts_tower¶: The number of actuator points along the tower for actuator-line/disk simulations.

actuator.nacelle_cd¶: The drag coefficient for the nacelle. If this is set to zero, or not defined, the code will not implement the nacelle model.

actuator.nacelle_area¶: The reference area for the nacelle. This is only used if the nacelle model is used.

actuator.air_density¶: The air density. This is only used to compute the nacelle force. It should match the density being used in both Nalu and OpenFAST.

actuator.epsilon¶: The spreading width \(\epsilon\) in the Gaussian spreading function in the [chordwise, thickness, spanwise] coordinate system to spread the forces from the actuator point to the nodes. In the case of the actuator disk, only the first value in the chordwise direction is used for the uniform isotropic Gaussian.

actuator.epsilon_chord¶: This is the ratio \(\epsilon/c\) in every direction [chordwise, thickness, spanwise]. If this option is specified, the code will choose a value of \(\epsilon\) at every location that is \(c * \epsilon/c\). To avoid numerical instabilities, the code will choose the maximum value between \(c * \epsilon/c\) and the value of actuator.epsilon_min specified.

actuator.epsilon_min¶: This is the minimum value of \(\epsilon\) in the Gaussian spreading function in the [chordwise, thickness, spanwise] coordinate system to spread the forces from the actuator point to the nodes. This option is required if the option actuator.epsilon_chord is specified.

actuator.epsilon_tower¶: The spreading width \(\epsilon\) in the Gaussian spreading function in the inertial [x, y, z] reference frame. If this value is not speficied, then actuator.epsilon or actuator.epsilon_min will be used.

actuator.restart_filename¶: The checkpoint file for this turbine when restarting a simulation

actuator.FAST_input_filename¶: The FAST input file for this turbine

actuator.turb_id¶: A unique turbine id for each turbine

actuator.num_swept_pts¶: This is an optional parameter specifically for actuator disks. This parameter determines the number of points that are placed azimuthally between the actuator lines and spread the forcing over the disk’s area. When num_swept_pts is included the number of azimuthal points between the lines is forced to this value at all radial locations. If num_swept_pts is omitted then the azimuthal sampling is computed automatically with different sampling at each radial location such that the average distance between points matches the radial spacing.