Alternate Fluids and Atmospheres
PropGen defines a fluid by the following 3 properties:
- density
- kinematic viscosity
- and sound speed.
If you're operating in normal air PropGen will internally compute those properties via well known formulae of the ISO International Standard Atmosphere (ISA).
For non-ISA environments you must manually specify density, kinematic viscosity, and sound speed. This makes it easy to work with arbitrary fluids; both liquids and gases. Sound speed is unlikely to matter for a liquid, but for a gas it's used to select the correct Mach polar. Kinematic viscosity is needed to compute Reynolds number and hence select the correct Reynolds polar... this, of course, becomes a "don't care" if you only have 1 Reynolds number in your polar dataset. Density is needed to get accurate physical computations - make sure this one is accurate!
Below is a diagram that illustrates how to switch between an ISO atmosphere and an arbitrary fluid. Examples utilizing these two options are also given with the latest distribution.
