Cavitation and hysteresis phenomena in oil flow through a rotating shaft with radial exit branches

Experimental study, dimensional analysis and computational analysis are conducted on air-oil two-phase flows in a prototype of power transmission lines in axial rotation. Oil is supplied into the lubricating system through one radial inlet duct, one hollow shaft, and one or two radial exit branches open to atmosphere. The branch-to-shaft diameter ratio, inlet oil flow rate, and rotational speed are varied.; In the experimental study, test sections are made transparent so as to observe the two-phase rotating flow patterns and measure the interfacial diameter in the shaft. Changes in time-average inlet pressure and exit oil flow rates are measured as functions of rotational speed for both spin-up and spin-down processes. Transitions of flow patterns in the shaft under the quasi-steady condition are plotted. It is disclosed that cavitation in the oil flow is induced by the intrusion of outside air into the shaft through the branch, featuring a high hydraulic head loss, against the exit oil flow. Hysteresis phenomena are also revealed for variations of oil flow rates, inlet pressure and flow patterns, and are due to the gaseous component contributing a nonlinear spring constant to the rotating system.; In the dimensional analysis, the air core diameter in the shaft is measured and correlated, and the void fraction is well predicted. Both plots of Reynolds number of oil film versus rotational Reynolds number and void fraction versus Rossby number show the possibility of dryout, the avoidance of which is critical to the lubrication of rotary devices. Heat transfer and evaporation that worsen the dryout are briefly discussed.; In the computational analysis, both the governing equations and empirical equations for hydraulic head losses and piping junctions are applied. Exit oil flow rates through identical twin branches are calculated for each two-phase flow regime, and the predicted results in the single-phase and annular flow regimes closely agree with the experimental data.; The present study can be applied to select proper lubricants or coolants and improve lubrication performance of rotating machinery such as automatic transmissions, power generators and gas turbines.