Direct numerical simulation of bifurcating jets

The mechanisms leading to bifurcating jets are investigated by means of dir ect numerical simulation. Two distinct types of jets were obtained by apply ing a bi-modal perturbation at the nozzle. When forcing simultaneously the counter-rotating helical modes (flapping mode) with the same amplitude and the same frequency, the jet splits into two branches, taking a distinct Y-s hape. A different evolution of the jet (Psi-shape) is observed when superpo sing the axisymmetric mode at the most amplified unstable frequency on the flapping mode with the same amplitude, but subharmonic frequency. In both c ases a spectacular increase of the jet spreading is observed. (C) 2000 Amer ican Institute of Physics. [S1070-6631(00)00404-9].