The Linearized Potential Flow, Boundary Mode Interface
The Linearized Potential Flow, Boundary Mode (lpfbm) interface (), found under the Acoustics>Aeroacoustics branch () when adding a physics interface, is used to compute eigenmodes and out-of-plane wave numbers for the linearized compressible potential flow equations. This study is used, for example, when specifying sources at inlets or analyzing transverse acoustic modes in ducts.
The physics interface solves an eigenvalue equation on boundaries, searching for the out-of-plane wave numbers at a given frequency.
When this physics interface is added, these default nodes are also added to the Model BuilderLinearized Potential Flow Model, Sound Hard Boundary (Wall), and Initial Values. For 2D axisymmetric models 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, Boundary Mode to select physics features from the context menu.
This physics interface is limited to flows with a Mach number Ma < 1, partly due to limitations in the potential flow formulation and partly due to the acoustic boundary settings needed for supersonic flow.
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 lpfbm.
Linearized Potential Flow Equation Settings
For 2D axisymmetric components, the Azimuthal mode number m (dimensionless) is 0 by default. It is an integer entering the axisymmetric expression for the velocity potential:
Sound Pressure Level Settings
The settings are the same as Sound Pressure Level Settings for the Pressure Acoustics, Frequency Domain interface.
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) 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