Study of Mixing and Combustion in the Presence of a Strong Streamwise Vorticity.(Dual Stream Axisymmetric Mixing in the Presence of Axial Vorticity)

摘要

An experimental investigation was undertaken to study the mixing process in acoaxial jet with an inner lobed mixer nozzle. Seven different inner jet nozzle geometries and also three different velocity ratios were explored. Flow visualizations using a passive scalar were performed using a laser sheet from a Nd:YAG laser as the light source. The laser has a 9 nsec pulse duration which effectively freezes the flow. Instantaneous cross sectional images were taken at various distances downstream as well as streamwise views. Quantitative information on the mixing was obtained by processing sets of images. The effects of various parameters such as the interfacial area increase due to the lobed nozzle geometry, The strength of streamwise vortices, and the large scale structures on the mixing process are evaluated and discussed. The results showed highly enhanced mixing as the strength of the streamwise vortices increased. The results also indicated that the presence of large scale structures due to the Kelvin-Helmholtz instabilities and their interaction with streamwise vortices generated by the lobes are crucial for enhanced mixing. The fraction of mixing enhancement due to streamwise vorticity (relative to mixing enhancement due to increased interfacial contact area) was found to increase as velocity ratio increased. In addition, this fraction increased with downstream distance.