PIV Measurements Around A Rotating Single Gear Partially Submerged In Oil Within Modelled SAAB Gearbox

Abstract

This study concerns fluid dynamics of the flow around a rotating single gear wheel which is partially submerged in oil within a modelled SAAB gearbox. A literature survey shows a very limited amount of studies on this topic which are publicly available at the moment. The experimental measurements were carried out by means of Particle Image Velocimetry (PIV) on this very highly complex flow. For the purpose of experimental study a test rig representing a simplfied model of a gearbox was built. The rig is specially designed for using PIV which means the optical access to the flow is maximized. The flow similarity with respect to a real gearbox is maintained and the working fluid is a transparent mineral oil. The wheel model is made interchangeable and the wheel rotation speed can be varied to investigate different operation conditions. Two different wheel models with a diameter of 220mm were considered in the measurement, one of them is smooth and the other one has spur teeth. At a very low rotational speed, (50rpm), the flow is mostly in one-phase below the oil level. As the rotational speed increases (400rpm), the flow pattern around the wheel become chaotic and two different two-phase flows with rotation, free-surface effects, and liquid splashing effects are involved. As the wheel rotates and splashing lead to the creation of oil droplets in the top part of the box and air bubbles are generated in the bottom part within the oil. At this stage the optical access become limited by partly from bubbles and oil splashing on the window. These bubbles cause problems due to optical refraction and distortion when laser light is illuminated on them. This issue was partly resolved by performing the experimental measurement in a "transient" mode. The transient mode was applied in such a way that a trigger signal was provided from the wheel to the PIV processor in order to allow immediate measurements suddenly after the rotation was started.