To set up a compressible flow in
FLUENT, you will need to follow the steps listed below. (Only those steps relevant specifically to the setup of compressible flows are listed here. You will need to set up the rest of the problem as usual.)
(You can think of
as the absolute static pressure at a point in the flow where you will define the gauge pressure
to be zero. See Section
8.14 for guidelines on setting the operating pressure. For time-dependent compressible flows, you may want to specify a floating operating pressure instead of a constant operating pressure. See Section
9.6.4 for details.)
Activate solution of the energy equation in the
(Pressure-based solver only) If you are modeling turbulent flow, activate the optional viscous
dissipation terms in the energy equation by turning on
Viscous Heating in the
Viscous Model panel. Note that these terms can be important in high-speed flows.
This step is not necessary if you are using one of the density-based solvers, because the density-based solvers always include the viscous dissipation terms in the energy equation.
Set boundary conditions (using the
Boundary Conditions panel), being sure to choose a well-posed boundary condition combination that is appropriate for the flow regime. See below for details. Recall that all inputs for pressure (either total pressure or static pressure) must be relative to the operating pressure, and the temperature inputs at inlets should be total (stagnation) temperatures,
not static temperatures.
These inputs should ensure a well-posed compressible flow problem. You will also want to consider special solution parameter settings, as noted in Section
9.6.5, before beginning the flow calculation.
Boundary Conditions for Compressible Flows
Well-posed inlet and exit boundary conditions for compressible flow
are listed below:
For flow inlets:
Pressure inlet: Inlet total temperature and total pressure and, for supersonic inlets, static pressure
Mass flow inlet: Inlet mass flow and total temperature
For flow exits:
Pressure outlet: Exit static pressure (ignored if flow is supersonic at the exit. All the information travels downstream in a supersonic region, hence the pressure at the outlet can be computed by directly extrapolating from the adjacent cell center [
143]. Therefore, it is not meaningful to use the exit static pressure prescribed in the boundary conditions panel, and the exit static pressure is ignored).
It is important to note that your boundary condition inputs for pressure (either total pressure or static pressure) must be in terms of gauge pressure--i.e., pressure relative to the operating pressure defined in the
Operating Conditions panel, as described above.
All temperature inputs at inlets should be total (stagnation) temperatures,
not static temperatures.