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.

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