Abstract
Axisymmetric jets issuing from pipe, nozzle and orifice were observed to investigate the effect of exit geometries on downstream behavior, using the hydrogen bubble method for flow visualization. It is found that the disturbance mode on the jet column depends on boundary layer thickness, δ, at the exit. A thin boundary layer produces varicose (axisymmetric) disturbances, while a thick boundary layer produce helical (non-axisymmetric) ones. The critical value of δ, which distinguishes one mode from the other, is determined as about 0.21 times the exit diameter. In the case of the varicose mode, position and frequency of vortex ring formation, transport velocity and frequency of coalescence are measured and correlated with the operating conditions. Considering the important role of δ on downstream behavior, the Strouhal number, Sr, for various exit conditions is generally defined by taking δ as the characteristic length. A single correlation for the proposed Sr is obtained independent of different exit conditions.
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