Implementation of a nozzle taking gas dynamic effects into account.
By default, the density is assumed to be constant across the
component. This assumption can be reverted by setting
assumeConstantDensity = false and hence the outlet
velocity is computed by the outlet density. Beware that this will
lead to a non-linear equation system in the component.
By definition, the sign of the velocity matches the sign of the mass-flow rate at the inlet.