Numerical simulations of elliptical jets: a study of jet entrainment

Free jets are naturally unstable. As a result the jet which is initially laminar becomes turbulent. During this transition process, large-scale structures are formed and fluid is "induced" to join the jet from the surroundings. This induction of fluid is defined as entrainment and depends greatly upon the jet geometry. In particular, an elliptical jet has been found to entrain at a higher rate than its circular counterpart. Numerical simulations of elliptical jets have been conducted on NRL’s parallel CM-5 and CM-200 supercomputers using the Flux Corrected Transport algorithm and initialized with the results of a linear stability analysis with the objective of investigating the entrainment process and explaining the dependence of the entrainment on jet geometry. Through the medium of scientific visualization, mechanisms responsible for entrainment have been identified and associated with the results of a linear stability analysis to suggest passive means by which entrainment can be enhanced. In particular, it was found that increasing the aspect ratio, thinning the shear layer, and non-uniformly distributing the shear layer serve to increase entrainment.