Formation of Air Core in Nozzles With Tangential Entry

The process of formation of air core and its development with time, inside one cylindrical and one conical nozzle having two tangential entries, has been analyzed experimentally and numerically. Experiments have been carried out using Plexiglas nozzles and water in ambient air; the air core has then been photographed for different nozzles and flow parameters. Numerical simulations have been performed using a finite volume method that employs unstructured grids with cell-wise local refinement and an interface-capturing scheme to predict the shape of the air core. The shape of the air core inside the cylindrical nozzle is found to be helicoidal at steady state for higher inlet velocity, whereas the shape of the free surface remains nearly cylindrical for low inlet velocity. In the conical nozzle, the air core is nearly axisymmetric in experiments. So only two-dimensional simulations are performed; the air core widens at the end of conical section as it approaches nozzle exit. For both nozzles numerical simulation predicts qualitatively and to a large extent also quantitatively the correct shape of the air core and the angle of the spray at the nozzle exit, as verified by comparisons with experimentally observed shapes.