The Linearized Potential Flow, Frequency Domain Interface
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.
The equations are formulated in the frequency domain and assume harmonic variation of all sources and fields. The physics interface is limited to flows with a Mach number Ma < 1, partly due to limitations in potential flow and partly due to the acoustic boundary settings needed for supersonic flow. The coupling between the acoustic field and the background flow does not include any predefined flow-induced noise.
When this physics interface is added, these default nodes are also added to the Model BuilderAeroacoustics 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.
Settings
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.
Linearized Potential Flow Equation Settings
For 1D axisymmetric components, the Azimuthal wave number m (dimensionless) is 0 by default. The Out-of-plane wave number kz (SI unit: rad/m) is 0 rad/m by default.
For 2D components, the Out-of-plane wave number kz (SI unit: rad/m) is 0 rad/m by default.
For 2D axisymmetric components the Azimuthal wave number m (dimensionless) is 0 by default.
Sound Pressure Level Settings
The settings are the same as Sound Pressure Level Settings for the Pressure Acoustics, Frequency Domain interface.
Typical Wave Speed
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.
Dependent Variables
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.
Discretization
From the list select the element order and type (Lagrange or serendipity) for the velocity potential, the default is Quadratic Lagrange.
Choosing between Lagrange and Serendipity Shape Functions has influence on the number of DOFs solved for and on stability for distorted mesh.
Flow Duct: Application Library path
Acoustics_Module/Aeroacoustics_and_Noise/flow_duct
Jet Pipe: Application Library Path
Acoustics_Module/Aeroacoustics_and_Noise/jet_pipe
Doppler Shift: Application Library path
Acoustics_Module/Aeroacoustics_and_Noise/doppler_shift