The Linearized Navier-Stokes, Frequency Domain (lnsf) interface (
), found under the
Acoustics>Aeroacoustics branch (
) when adding a physics interface, is used to compute the acoustic variations in pressure, velocity, and temperature in the presence of any stationary isothermal or nonisothermal background mean flow. The physics interface is used for aeroacoustic simulations that can be described by the linearized Navier-Stokes equations.
The equations defined by the Linearized Navier-Stokes, Frequency Domain interface are the linearized continuity, momentum (Navier-Stokes), and energy equations. The physics interface solves for the acoustic variations in the pressure p, velocity field
u, and temperature
T. The harmonic variation of all fields and sources is given by
using the
+iω convention. The equations are formulated in the frequency domain for any fluid including losses due to viscosity and thermal conduction. The background mean flow can be any stationary flow.
When this physics interface is added, these default nodes are also added to the Model Builder —
Linearized Navier-Stokes Model,
Wall, and
Initial Values. For axisymmetric components, an
Axial Symmetry node is also added.
Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and sources. You can also right-click
Linearized Navier-Stokes, Frequency Domain to select physics features from the context menu.
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern
<name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the
name string must be unique. Only letters, numbers, and underscores (_) are permitted in the
Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is
lnsf.
Expand the Equation section to see the equations solved for with the
Equation form specified. The default selection is
Equation form is set to
Study controlled. The available studies are selected under
Show equations assuming.
Click to select Adiabatic formulation to use an adiabatic equation of state and disable the temperature degree of freedom for the linearized Navier-Stokes equations. This formulation is applicable when the thermal losses can be disregarded, this is often the case in liquids like water. In gases, like air, on the other hand the full formulation is necessary. When
Adiabatic formulation is selected, all temperature conditions and options are disabled in the user interface.
For all component dimensions, and if required, click to expand the Equation section, then select
Frequency domain as the
Equation form and enter the settings as described below.
The default Scaling factor Δ is 1
/(
iω). This values correspond to the equations for a Frequency Domain study when the equations are study controlled. To get the equations corresponding to an Eigenfrequency study, change the
Scaling factor Δ to 1. Changing the scaling factor influences the coupling to other physics.
See Sound Pressure Level Settings for the Pressure Acoustics, Frequency Domain interface.
See Typical Wave Speed for the Pressure Acoustics, Frequency Domain interface.
This physics interface defines these dependent variables (fields), the Pressure p, Velocity field u and its components, and
Temperature variation T. The name can be changed but the names of fields and dependent variables must be unique within a model.
Select the Stabilization Method —
No stabilization applied,
Galerkin least squares (GLS) stabilization (the default),
Streamline upwind Petrov-Galerkin (SUPG) stabilization, or
Streamline diffusion (legacy method). When stabilization is selected enter a value for the
Stabilization constant αstab (dimensionless). The default value is
1e-2 and should typically have a numerical value between
1 and
1e-3.