Section: Momentum Sources

ICNS.source_terms

type: String(s), optional

Activates source terms for the incompressible Navier-Stokes momentum equations. These strings can be entered in any order with a space between each. Please consult the AMR-Wind API for a comprehensive list of all momentum source terms available. Note that the following input arguments specific to each source term will only be active if the corresponding source term (the root name) is listed in ICNS.source_terms.

BoussinesqBuoyancy.reference_temperature

type: Real, mandatory

Reference temperature \(\theta_\mathrm{ref}\) in Kelvin. Values of the temperature field that are less than or greater than this value will cause a buoyancy force in the direction of the gravity vector.

BoussinesqBuoyancy.thermal_expansion_coeff

type: Real, optional, default \(\beta = 1 / \theta_\mathrm{ref}\)

Thermal expansion coefficient, if not specified this value is set to the inverse of the BoussinesqBuoyancy.reference_temperature value.

CoriolisForcing.latitude

type: Real, mandatory

Latitude in degrees where the Coriolis forcing is computed. Positive values indicate northern hemisphere.

CoriolisForcing.rotational_time_period

type: Real, optional, default = 86400.0

Rotational time period of a day in seconds.

CoriolisForcing.east_vector

type: List of 3 reals, optional, default = 1.0 0.0 0.0

East vector that gives the orientation of the grid w.r.t. to planetary coordinate system. This vector is automatically normalized within amr-wind.

CoriolisForcing.north_vector

type: List of 3 reals, optional, default = 0.0 1.0 0.0

North vector that gives the orientation of the grid w.r.t. to planetary coordinate system. This vector is automatically normalized within amr-wind.

GeostrophicForcing.geostrophic_wind

type: List of 3 reals, optional

The user has to choose between GeostrophicForcing and ABLForcing. CoriolisForcing input must be present when using GeostrophicForcing. These checks are not enforced for now.

GeostrophicForcing.geostrophic_wind_timetable

type: String, optional

Input file name for table that lists time in seconds, wind speed in meters per second, and horizontal wind direction in degrees of the Geostrophic forcing velocity. Each line in the file should be a sequence of three floats specifying the inputs in that order (e.g., 0.0 8.0 -5.0). If this argument is present, the GeostrophicForcing.geostrophic_wind will be ignored. Note that the code expects there to be a single-line header at the beginning of the geostrophic wind timetable file; if no header exists, the first line of data will be ignored.

ABLForcing.abl_forcing_height

type: Real, mandatory

Height in meters at which the flow is forced to maintain the freestream inflow velocities specified through incflo.velocity.

ABLForcing.velocity_timetable

type: String, optional

Input file name for table that lists time in seconds, wind speed in meters per second, and horizontal wind direction in degrees of the ABL forcing velocity. Each line in the file should be a sequence of three floats specifying the inputs in that order (e.g., 0.0 8.0 -5.0). If this argument is present, the incflo.velocity argument will be ignored. Note that the code expects there to be a single-line header at the beginning of the velocity timetable file; if no header exists, the first line of data will be ignored.

ABLForcing.forcing_timetable_output_file

type: String, optional

Output file name for writing the ABL forcing vector to a text file over the course of a simulation. This output is primarily intended for replicating the ABL forcing from a precursor simulation in a subsequent inflow-outflow simulation by providing an input file for Body Forcing. The output file will contain the time and three vector components of the force.

ABLForcing.forcing_timetable_frequency

type: Int, optional

The interval of timesteps for writing to the forcing timetable output file. The default is 1, i.e., writing every step, which is also the default of the boundary plane output feature.

ABLForcing.forcing_timetable_start_time

type: Real, optional

The start time for writing to the forcing timetable output file. The default is 0.

ABLForcing.abl_forcing_off_height

type: Real, required for multiphase simulations with ABL

This parameter indicates the vertical distance above the water level that the ABL forcing term should be turned off. This tuning parameter is used to avoid applying the ABL forcing to ocean waves. This is not used when the volume fraction field (vof) is not present in the simulation.

ABLForcing.abl_forcing_ramp_height

type: Real, required for multiphase simulations with ABL

This parameter indicates the vertical distance above the water level and the “off height” that the ABL forcing term should ramp up from zero to full strength. This is not used when the volume fraction field (vof) is not present in the simulation.

ABLForcing.abl_forcing_band

type: Real, optional for multiphase simulations with ABL

This parameter is an additional safeguard against applying ABL forcing within the waves. This specifies the number of computational cells in a band around the air-water interface that the ABL forcing should be deactivated. While the other arguments relate to the height coordinate within the domain, this argument is relative to the actual position of water in the simulation. The default value is 2.

BodyForce.type

type: String, optional

The type of body force being used. The default is uniform_constant, which applies a single constant force vector over the entire domain. Other available types are height_varying, oscillatory, and uniform_constant.

BodyForce.magnitude

type: List of 3 reals, conditionally mandatory

The force vector to be applied as a body force. This argument is mandatory for uniform_constant (default) and oscillatory body force types.

BodyForce.angular_frequency

type: Real, conditionally mandatory

The angular frequency to be used for applying sinusoidal time variation to the body force. This argument is mandatory for the oscillatory body force type and is only active for the oscillatory type.

BodyForce.bodyforce_file

type: String, conditionally mandatory

The text file for specifying the body force vector as a function of height. This text file must contain heights (z coordinate values), force components in x, and force components in y. This argument is mandatory for the height_varying body force type and is only active for the height_varying type.

BodyForce.uniform_timetable_file

type: String, conditionally mandatory

The text file for specifying the body force vector as a function of time. This text file must contain times, force components in x, force components in y, and force components in z. This argument is mandatory for the uniform_timetable body force type and is only active for the uniform_timetable type. Note that the code expects there to be a single-line header at the beginning of the uniform timetable file; if no header exists, the first line of data will be ignored.

DragForcing.drag_coefficient

type: Real, optional

This value specifies the coefficient for the forcing term in the immersed boundary forcing method. It is currently recommended to use the default value to avoid initial numerical stability.

DragForcing.sponge_strength

type: Real, optional

The value of the sponge layer coefficient. It is recommended to use the default value of 1.0.

DragForcing.sponge_density

type: Real, optional

The value of the sponge layer density. It is recommended to use the default value of 1.0.

DragForcing.sponge_distance_west

type: Real, optional

This value is specified as a negative value when the inflow x-velocity is <=0. The default value is -1000 m and can be changed if strong reflections are observed.

DragForcing.sponge_distance_east

type: Real, optional

This value is specified as a positive value when the inflow x-velocity is >=0. The default value is 1000 m and can be changed if strong reflections are observed.

DragForcing.sponge_distance_south

type: Real, optional

This value is specified as a negative value when the inflow y-velocity is <=0. The default value is -1000 m and can be changed if strong reflections are observed.

DragForcing.sponge_distance_north

type: Real, optional

This value is specified as a positive value when the inflow y-velocity is >=0. The default value is 1000 m and can be changed if strong reflections are observed.

DragForcing.sponge_west

type: int, optional

This term turns on the sponge layer in the west (-x) boundary. The default value is 0.

DragForcing.sponge_east

type: int, optional

This term turns on the sponge layer in the east (+x) boundary. The default value is 1.

DragForcing.sponge_south

type: int, optional

This term turns on the sponge layer in the south (-y) boundary. The default value is 0.

DragForcing.sponge_north

type: int, optional

This term turns on the sponge layer in the north (+y) boundary. The default value is 1.

DragForcing.is_laminar

type: int, optional

This term turns off the sponge layer. This term is required for terrain simulations with periodic boundary conditions. The default value is 0.

The following arguments are influential when GravityForcing is included in ICNS.source_terms.

ICNS.use_perturb_pressure

type: Boolean, optional, default = false

When this option is off, the GravityForcing term is simply \(g\), which becomes \(\rho g\) when included in the momentum equation. By activating this option, the momentum term applied by GravityForcing will become \((\rho - \rho_0) g\), where \(rho_0\) is some constant reference density profile. The reference density field can be created by either MultiPhase physics or anelastic ABL physics. By using the reference density, the pressure field seen by the solver is represented as a perturbation from a reference pressure field, enabling pressure_outflow boundary conditions to better handle certain flows, e.g., those with equilibrium pressure gradients parallel to the outflow plane.

ICNS.reconstruct_true_pressure

type: Boolean, optional, default = false

This option is only valid when the perturbational pressure form is being used, i.e., ICNS.use_perturb_pressure = true. Reconstructing the true pressure adds back the reference pressure profile to obtain the full pressure after the pressure solve has been performed. This makes no difference to the flow evolution, but it changes the field available for post-processing or coupling to overset solvers.