SIMULATION OF AXISYMMETRICAL JET ISSUING FROM A NOZZLE WITH COLLAR

The evolution of a round turbulent jet issuing from a nozzle with a collar is simulated by using a discrete vortex method under the constraint of axial symmetry. The vortex sheets shed from the nozzle and the edge of the collar are represented by vortex ring elements. The collar is represented by vortex rings of appropriate strengths to satisfy the no-through-flow condition. The effect of the collar on the development of the jet shear layer is investigated with and without harmonic excitation. When harmonic excitation in the range of St=0.3 to 0.7 is applied to the model jet issuing from a nozzle without a collar, large-eddy structures corresponding to the frequency of the excitation are formed. When St greater-than-or-equal-to 0.5, these eddies coalesce immediately and are converted into eddies of St/2. The evolution of the jet shear layer is greatly affected by the collar. The preferred frequency varies with the dimensions of the collar.