Mixing of transversely injected jets into a crossflow under low-density conditions

The objective of this study is to investigate experimentally the mixing of transversely injected jets into a cross-flow under low-density conditions. This study has application in nitrogen-diluted subsonic chemical oxygen iodine lasers. The investigation was performed nonintrusively, using planar-laser-induced fluorescence. A frequency doubled Nd:YAG laser was used as the excitation source, and the iodine fluorescence was imaged using a charge-coupled device camera. Experiments were performed for a variety of crossflow velocities and injection pressures. A parameter, degree of unmixedness, which was defined using variance of the image intensities, was used to quantity the mixing. Mixing distance was defined as the location downstream of which the degree of unmixedness did not exceed 0.05. The mixing distances obtained were correlated using the ratio between the momentum flow rates of the injected jets and the crossflow. The mixing distances were linearly dependent on this ratio until a value more than which the jets mixed almost at the injection location. This linearity depended on the injection configuration. The correlation was found to be a weak function of the injector hole diameter. Diffusion is the main mixing mechanism in this low-Reynolds-number flow regime, and thus the spatial distribution of the injector holes in the array played an important role in mixing.