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

In order to reduce oil dynamic power loss in aeroengine gearboxes, visualizations and measurements of the oil-flow are effective. In the research presented in this paper, we developed a flow visualization borescope which can qualitatively visualize oil flow and a two-phase flow probe which can quantitatively measure oil/air ratio and the flow velocity. The flow visualization borescope consists of a 16mm diameter pipe in which an air purge passage for removing oil mist and a borescope are integrated with an illumination laser light and optical lenses, enabling clear high-speed photography. The two-phase probe consists of a 5mm diameter pipe with a 1mm diameter measurement hole and has a pressure adjustment pipe inside the pipe. For a demonstration, a shrouded spur gear with 100 m/s peripheral speed and 20 liters/min oil supply was used. Flow visualization at 30000 frame/sec imaging shows that oil outflow from the shroud opening spreads turbulently over the whole width of the opening. Oil/air ratio and flow velocity measurement by the two-phase flow probe show that there was thin oil-rich layer on the shroud wall and the flow speed was slow compared with the gear peripheral speed. The measurement equipment we developed was easily installed to the gearbox and therefore it is expected to apply to real aeroengine gearboxes.