The Thermodynamics of Air at High Velocities

Abstract

The flow of air at velocities near and above sound velocity is involved in an ever-increasing number of cases, and a satisfactory solution often requires the use of the highly specialized tools of modern fluid mechanics. However, there are many engineering problems that may be solved with sufficient accuracy in terms of average velocities without following through the paths of individual particles. When these thermodynamic equations of high velocity gas flow are solved in terms of such variables as velocity and density, they are not simple or easy to handle. If Mach number is used as a primary variable, all of these equations become quite simple and usable. This is illustrated by the solution of the cases of flow with friction and with heat transfer and for nozzles and diffusers with and without friction. Diffusers are discussed in more detail and measures of diffuser performance are suggested because, in proportion to their importance, they have received far less attention than nozzles. In conclusion, the case of flow through plane shock waves is solved in terms of Mach number and the theoretical correction for impact tubes in superacoustic flow is worked out.