Crocco's theorem
Crocco's theorem is an aerodynamic theorem relating the flow velocity, vorticity, and stagnation pressure (or entropy) of a potential flow. Crocco's theorem gives the relation between the thermodynamics and fluid kinematics. The theorem was first enunciated by Alexander Friedmann for the particular case of a perfect gas and published in 1922: However, usually this theorem is connected with the name of Italian scientist Luigi Crocco, a son of Gaetano Crocco. Consider an element of fluid in the flow field subjected to translational and rotational motion: because stagnation pressure loss and entropy generation can be viewed  as essentially the same thing, there are three popular forms for writing Crocco's theorem: In the above equations, formula_5 is the flow velocity vector, formula_6 is the vorticity, formula_7 is the specific volume, formula_8 is the stagnation pressure, formula_9 is temperature, formula_10 is specific entropy, formula_11 is specific enthalpy, formula_12 is specific body force, and formula_13 is the direction normal to the streamlines. All quantities considered (entropy, enthalpy, and body force) are "specific", in the sense of "per unit mass".