The Linearized Euler, Frequency Domain (lef) interface (), found under the Acoustics>Aeroacoustics branch () when adding a physics interface, is used to compute the acoustic variations in density, velocity, and pressure in the presence of a stationary background mean-flow that is well approximated by an ideal gas flow. The physics interface is used for aeroacoustic simulations that can be described by the linearized Euler equations.

The equations defined by the Linearized Euler, Frequency Domain interface are the linearized continuity, momentum (Euler), and energy equations. The physics interface solves for the acoustic variations in the density ρ, velocity field u, and pressure p. The equations are formulated in the frequency domain and assume harmonic variation of all sources and fields. The background mean flow can be any stationary gas flow that is well approximated by an ideal gas. The coupling between the acoustic field and the background flow does not include any predefined flow induced noise. Even though the equations do not include any loss mechanisms, only acoustic modes exist in the frequency domain as the driving frequency is predefined and real valued.

The equations are implemented in the so-called scattered field formulation. All equations and boundary conditions are formulated in the total acoustic fields
(ρt, ut, pt). The total fields are in the presence of the Background Acoustic Fields feature the sum of the background (ρb, ub, pb) and the scattered field (ρ, u, p):

When this physics interface is added, these default nodes are also added to the Model Builder — Linearized Euler Model, Rigid 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 Euler, 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 lef.

See Sound Pressure Level Settings for the Pressure Acoustics, Frequency Domain interface. Only Use reference pressure for air or User-defined reference pressure are available selections.

See Typical Wave Speed for the Pressure Acoustics, Frequency Domain interface.

This physics interface defines these dependent variables (fields), the Density rho, Velocity field u and its components, and Pressure p. The name can be changed but the names of fields and dependent variables must be unique within a model.

To display this section, click the Show button () and select Stabilization. The Streamline diffusion check box is selected by default and the Stabilization parameter αSD (dimensionless) default is 5·10-3. Click to clear the check box as required.

The stabilization scheme implements the streamline upwind Petrov-Galerkin (SUPG) formulation of the weak form equations used for the finite element method. The stabilization parameter αSD can be tuned depending on the problem solved, the nature of the background mean flow, and on the computational mesh. The implementation follows the one discussed in Ref. 10 and Ref. 14.

To display this section, click the Show button () and select Discretization. From the list select the element order and type (Lagrange or serendipity) the default is Linear for all the dependent variables.