Compressibility Effects in Aerodynamics

A few decades ago the most enthusiastic admirer of mathematical analysis would not have expected that practical engineers engaged in the design of aircraft would have so much use for the mathematical theory of fluid motion as is the case in modern aeronautical engineering. The various applications of the theory are based almost entirely on the hydrodynamics of incompressible perfect fluids, a discipline that half a century ago was considered as an interesting field of pure science having very little to do with the motion which actually takes place in a real fluid. Recently, interest has been centered on another branch of fluid mechanics, namely, on the mechanics of compressible fluids. The aeronautical engineer is pounding hard on the closed door leading into the field of supersonic motion. He realizes that the price that has to be paid for further increase of speed becomes higher and higher if he nears this frontier. However, he wonders whether the mathematical theory could not be used as a guide for avoiding a premature drop of aerodynamic efficiency. The present paper has the objective of reviewing the present status of the theory of compressible fluids from the practical standpoint of its usefulness for interpretation of experimental research and guidance in design.