Development of a Flow Visualization Borescope and a Two-Phase Flow Probe for Aeroengine Transmission Gears

Abstract

To reduce power losses due to oil flows in aeroengine gearboxes, the oil flows should be visualized and measured. In this study, we develop a flow visualization borescope that qualitatively visualizes oil flows along with a two-phase flow probe that quantitatively measures the oil/air ratio and flow velocity. The flow visualization borescope comprises a 16-mm-diameter pipe. Within the pipe, an air purge passage for removing oil mist and a borescope are integrated with an illumination laser and optical lenses, enabling clear, high-speed photography. The two-phase probe consists of a 5-mm-diameter pipe with a 1-mm-diameter measurement hole and an internal pressure adjustment pipe. The borescope and flow probe were demonstrated using a shrouded spur gear with a peripheral speed of 100 m/s and oil supply of 20 l/min. Flow visualization at 30,000 fps revealed that oil outflow from the shroud opening spreads turbulently over the entire width of the opening. Measurements of the oil/air ratio and flow velocity using the two-phase flow probe revealed a thin oil-rich layer on the shroud wall and showed that the flow speed is lower than the gear peripheral speed. The measurement equipment used herein would be easy to install in a gearbox and is therefore expected to be applied in actual aeroengine gearboxes.