The Linearized Potential Flow, Frequency Domain (lpff) interface (
), found under the
Acoustics>Aeroacoustics branch (
) when adding a physics interface, is used to compute the acoustic variations in the velocity potential in the presence of an inviscid and irrotational background mean flow, that is, a potential flow. The background flow can be modeled using
The Compressible Potential Flow Interface. The physics interface is used for convected acoustic simulations that can be described by the linearized compressible potential flow equations.
When this physics interface is added, these default nodes are also added to the Model Builder —
Aeroacoustics Model,
Sound Hard Boundary (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 Potential Flow, 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
lpff.
The settings are the same as Sound Pressure Level Settings for the Pressure Acoustics, Frequency Domain interface.
Select the Port sweep setting as No port sweep (the default) or
Activate port sweep to enable the port sweep functionality
. The
Activate port sweep option is used to compute the full scattering matrix when
Port conditions are used.
Select the Mode shape normalization as
Amplitude normalization (the default),
Power normalization, or
Intensity normalization. This setting controls if the pressure mode shapes
pn are normalized to have a unit maximum amplitude or carry unit power or intensity. The intensity and power normalization are usually used for convective acoustic simulations in jet turbofan noise modeling,
Ref. 24 and
Ref. 25. The selection determines how the scattering matrix is to be interpreted.
The Amplitude normalization ensures that
max(|
pn|) = 1, the
Power normalization ensures that the pressure modes fulfill
where A is the port areas. Finally, the
Intensity normalization gives
Enter a value or expression for the Typical wave speed for perfectly matched layers cref (SI unit m/s). The default is
lpff.c0 and the value is automatically taken from the material model. If several materials or material models are used, it is best practice to add one PML for each. This will ensure that the typical wavelength is continuous within each PML feature.
For convected acoustic problems, it can be necessary to set the value of the Typical wavelength from option in the PML feature manually, to correct for the convected background velocity.
This physics interface defines one dependent variable (field), the Velocity potential phi. The name can be changed but the names of fields and dependent variables must be unique within a model.
.
