Theoretical and experimental investigation of the compressible free mixing of two dissimilar gases.

An extension and improvement of Warren's momentum integral method for predicting the turbulent mixing and decay of axially symmetric, compressible, free jets to the case of the mixing of dissimilar gases is discussed. Two ideal gases having different molecular weights and specific heats are treated with the assumption that the local turbulent mixing rate at each axial location depends upon a suitably chosen local reference Mach number. This method of analysis is then compared with the results of a series of jet-mixing experiments carried out on helium, methane, nitrogen, carbon dioxide, and freon jets mixing in air. Mach numbers ranging from 0.75 to 3.30 were investigated. The character and mixing rates of both properly and improperly expanded supersonic jets were studied. It is concluded from a comparison of these data with the theoretical method presented that a general relationship exists, at each axial position in the jet, between a local mixing rate parameter and the local Mach number. This general relationship is independent, within the accuracy of these experiments, of the physical properties or the thermodynamic state of the mixing gases.