generally speaking it refers to constant density or variable density. In practical terms density changes start to become significant around 0.3 Mach number though you could argue that number up and down a bit - lowest I have seen if 0.2 Mach. Flow sim handles it for you so no issue. The high Mach number setting is for flow that are dominated by flows over Mach 1.
here is what the help says:In Flow Simulation, gases are always compressible and liquids can be incompressible or compressible. If your project deals with a high-velocity gas flow, where the Mach number maximum value exceeds about 3 for steady-state analyses or 1 for transient (time-dependent) analyses, you should consider the gas flow as a high Mach number flow. To consider high Mach number gas flow, select the High Mach number flow check box either on the Default Fluids step of the Wizard or in the Fluids dialog box in General Settings.The low Mach number gas flow is recommended for the tasks where the supersonic flow is localized in relatively small fluid volume and the major flow is subsonic. If the fluid volume in which the flow becomes supersonic is about a half of the computational domain size or greater, it is recommended that you consider the flow as a high Mach number gas flow.
Hi Bill, I'm involved in a proyect where the mach number is around 1.5 maybe 2 Mach, but when you select rotational in the general settings you can't find the option check box of high mach number. So, I would like to know whether there is another way to select this option or not. The problem I got is that my flow sim. is no converging and an error messagge is showed in my screen, please check my discussion to figure out what I mean.
I hope you can help me