The turbulent structure and entrainment of nonpremixed jet flames were investigated under normal- and low-gravity conditions. The flames were studied by using planar laser Mie scattering (PLMS) applied at normal gravity and in the UT-Austin 1.25-second drop tower. Experiments were conducted in piloted propane and ethylene jet flames at a Reynolds number of 5000, in normal and milligravity conditions. The entrainment was determined from the mean centerline mixture fraction decay inferred from the PLMS images. The normal gravity flames were seen to entrain more than the milligravity flames when the local buoyancy parameter was approximately greater than 2. Furthermore, the mean mixture fraction measurements show that momentum-dominated nonreacting and reacting jets obey a universal scaling law when heat release effects are accounted for, using a modified source diameter. A mixing model to predict the flame length of momentum-dominated, turbulent jet flames was also developed and tested. The instantaneous PLMS images for the propane and ethylene flames reveal that the milligravity flames exhibit large-scale structures that are thicker and greater in number than the normal gravity flames at the same Reynolds number. The RMS intermittency fields computed from the instantaneous PLMS images show strong similarities in the upstream third of the flames. Farther downstream, however, the milligravity flames exhibit clear differences from the normal gravity flames, which are attributed to buoyancy effects.
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