Solver Suggestions for Large Aeroacoustic Models
Studying aeroacoustic applications often lead to very large models that can contain many degrees of freedom (DOFs). Different steps can be taken to reduce the models size, for example, consider the use of slip instead of no-slip conditions in the LNS interface (avoiding the details in the acoustic boundary layer) or consider the choice between Lagrange and Serendipity Shape Functions.
When a model reaches a size where it can no longer fit in memory (when solved using the default direct solver) or if the solution procedure is slow with a direct solver, then it can be advantageous to switch to an iterative solver approach.
For the Linearized Navier-Stokes interfaces iterative solver suggestions are automatically generated when the default solver is generated. These can be seen by expanding the Solver Configuration tree under Stationary Solver or Time-Dependent Solver. Per default a direct solver is used and two iterative solvers are suggested and disabled. To turn on one of these approached right-click the solver and select Enable (or press F4). The first suggestion (GMRES with Direct Precon.) uses an iterative solver with a direct preconditioner. This method is typically faster then the direct solver and uses 20% less memory. The second suggestion (GMRES with DD) uses an iterative solver with the domain decomposition method. This method is very robust (also for multiphysics applications) and very memory efficient, but it can be slow.
For the Linearized Euler interfaces the default solver is PARDISO, which is also the most robust option. Iterative solver will often struggle for the linearized Euler equations because there is not dissipation involved and instabilities are inherent.
Further details on solving large models can be found in the Solver Suggestions for Large Thermoviscous Acoustics Models section. These suggestions also apply to the linearized Navier-Stokes physics.
Solving in the Adiabatic Case
In certain cases, it is a good assumption to not include thermal conduction in the model and treat all processes as adiabatic (isentropic). This is, for example, relevant for fluids where the thermal boundary layer is much thinner than the viscous, like in water. Not solving for the temperature field T also saves some degrees of freedom (DOFs).
This is achieved by selecting the Adiabatic formulation option under the Linearized Navier-Stokes Equation Settings section. When Adiabatic formulation is selected all temperature options and conditions are disabled in the user interface.