The Compressible Euler Equations (cee) interface (), found under the Fluid Flow>High Mach Number Flow branch () when adding a physics interface, is used to model transient isentropic gas flows where the velocity magnitude is comparable to the speed of sound, that is, compressible flows in the transonic and supersonic range. This state is often connected to very low pressures.

The interface is based on the discontinuous Galerkin method (DG-FEM) and uses a time-explicit solver. The method is very memory lean. The physics interface solves for conservation of mass, momentum, and energy, neglecting dissipative effects. The dependent variables are the density, momentum, and total energy. Simulations using the Compressible Euler Equations interface are always time dependent.

When this physics interface is added, the following default nodes are also added in the Model Builder — Fluid Properties, Initial Values, and Wall. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions, volume forces, and heat sources. You can also right-click the Compressible Euler Equations node 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 cee.

When the Include gravity check box is selected, a global Gravity feature is shown in the interface model tree, and the buoyancy force is included in the Euler equations.

To display this section, click the Show More Options button () and select Stabilization in the Show More Options dialog box. Normally these settings do not need to be changed.

Select the Numerical flux — Lax-Friedrichs (the default) or Osher-Solomon Riemann solver.

To display this section, click the Show More Options button () and select Stabilization in the Show More Options dialog box. Normally these settings do not need to be changed. Note that these settings are ignored when the discretization is set to Constant.

If the WENO limiter is selected from the Limiter list, the following settings are available:

To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. Normally these settings do not need to be changed.

Select the CFL number. This CFL number will be used when defining the Cell time scale expression cee.wtc used in the Time-Explicit Solver if the Time stepping is set to From expressions. Note that the method will be unstable for CFL numbers larger than 1.

In this section you can select the order of the shape function of the dependent variables. The Compressible Euler Equations interfaces uses Nodal discontinuous Lagrange functions. Select the Element order — Linear (default) or Constant.

The dependent variables (field variables) are the Density rho (SI unit: kg/m3), the Momentum m (SI unit: kg/(m2 s)), and the Total energy etot (SI unit: J/m3). The names can be changed but the names of fields and dependent variables must be unique within a component.