Hysteresis and bifurcation of flow in fuel injection nozzles

Separated flows due to cavitation and attached flows with and without cavit ation are investigated for sharp-edged nozzles. The influence of the nozzle diameter, length-diameter ratio and Reynolds number on the bifurcation bet ween the two states of flow is determined. A zone of hysteresis is seen to be present in small sharp-edged nozzles having length-diameter ratios of ab out 1.5-5 owing to a delayed bifurcation from cavitated flow to attached fl ow. The role of nozzle diameters and imperfections in the sharp-edged entry is determined, The onset of separated flows arising from cavitation and su bsequent reattachment due to cessation of cavitation occur at threshold val ues of the cavitation number which vary with the nozzle diameter and the le ngth-diameter ratio. The time for transition from cavitated flow to attache d flow is discussed.