# Set Up Compressible Flow Modeling

Simulate high speed flows with speeds ranging from subsonic to transonic up through low supersonic conditions. Compressible flow simulations should be conducted using a transient analysis with ideal gas properties for air. AcuSolve will compute the coupled system of compressible NS equations with a single non-linear iteration using the "compressible_flow" stagger. Compressible flow is compatible with the supported turbulence models and most other existing AcuSolve features

1. From the Flow ribbon, click the Physics tool.
2. Under the Physics models settings, set the flow radio buttons to Single phase and Supersonic.
3. Select an ideal gas model or open the Material Library to create and edit material models.
4. Use the Material tool on the Flow ribbon to assign the ideal gas material to the solid body.
5. Define inlet boundaries with velocity, temperature, or pressure.

For velocity and temperature, you can use the mach number calculator to identify the velocity value.

6. Define initial conditions for pressure and temperature.
Tip:
General usage
• Analysis must be transient.
• Heat transfer should be on with or without turbulence active.
Inflow boundary conditions
• Stagnation pressure inlet and static pressure outflow are the preferred boundary condition specifications.
• Subsonic conditions require two variables as input while supersonic conditions require three.
• Mach number is computed by $Mach=\sqrt{\gamma RT}$ and positivity of both pressure and temperature are checked by AcuPrep.
• When the specified inflow condition is subsonic, pressure is ignored, and only velocity or Mach number and temperature are used as the boundary conditions.
Outflow boundary conditions
• Subsonic: The user-specified pressure is fixed.
• Supersonic: The user-specified pressure is ignored if it is lower than the computed pressure on the outflow surface.
Nodal initial conditions
• It is important (critical in most cases) to specify valid initial values for all the solution quantities. Pressure and temperature must be defined such that density is realistic.