Bubble shape and orientation determination with a four-point optical fibre probe

We propose a new method to estimate the aspect ratio and orientation of bubbles by using their time series obtained with a four-point optical-fibre probe. The feasibility and accuracy of the method was first analysed by using synthetic bubble-probe interaction data and single bubble experiments in pure water. Reasonable comparisons between this new technique and image analysis results were obtained. As a next step, the technique is applied to a vertical bubbly pipe flow at high void fraction. The typical bubble spherical equivalent diameter is 2-8 mm. The results provided by these measurements are compared with an available bubble aspect ratio correlation. A reasonable agreement is found. Some first results about the bubble orientation changes with bubble shape in bubbly shear flows are also presented.