A modified Thring-Newby scaling criterion for confined, rapidly spreading, and unsteady jets

Abstract

Burner systems employing rapidly spreading jets have received considerable attention and found niche markets in combustion applications. However, there is limited information on their scalar mixing characteristics and none under confined conditions. Existing scaling criteria for the prediction of industrial flames using physical or computational models have limited application to practical combustion systems employing such burners. New scalar concentration measurements are obtained for confined precessing jet flows, a class of rapidly spreading jet, using planar laser-induced fluorescence. The measurements assess the effects of coflow and confinement to provide new physical insight and empirical data for the development of physical and computational models. The scalar measurements are used to derive a new scaling procedure for these flows. Compared with existing criteria, the proposed scaling method achieves improved mixing similarity between two systems employing different fluids at different scales. This is accomplished by distorting the confinement ratio according to a modified form of the well-known Thring-Newby parameter and by incorporating an additional distortion to the stoichiometry. The approach is general and can also be applied to other rapidly spreading jet flows given appropriate empirical data.