Gas jets in an arbitrary stream

Abstract

AbstractSelf-preserving turbulent flows in the farfield of binary gas jets in an arbitrary stream are investigated. The governing equations solved are valid for jet flows only and are not applicable to wake flows where a linearised set of boundary layer equations are more appropriate. Gaussian error-functions are assumed for the mean excess velocity and mass fraction distributions. Thus formulated, the eddy diffusivities for momentum and mass are evaluated by solving the governing equations and are shown to vary across and along the jet. A condition is imposed on the eddy momentum diffusivity so that it correctly approaches the limiting behaviour for the case of an incompressible free round jet. This condition gives rise to an auxiliary equation for the determination of the decay of centreline properties and jet growth. The new and more general auxiliary equation is shown to model fluid entrainment and to reduce correctly to previous equations derived for the special cases of free gas jets and incompressible heated jets in a co-flowing stream. Thus deduced, the new auxiliary equation is solved together with other conservation equations to yield a set of growth rate and decay laws. The derived growth rate and decay laws correctly approach the various laws derived earlier for different special cases and correlate well with experimental measurements reported in the literature. The present solutions also represent solutions for compressible jets in a general stream where the pressure field is constant. Finally, this approach of analysing the self-preserving mean jet flow is also applicable to the study of wake flows where the linearised boundary-layer equations are solved.