Void Fraction and Speed of Sound Measurement in Cavitating Flows by the Three Pressure Transducers (3pt) Technique

Abstract

Speed of sound and void fraction are two key parameters in the characterisation of two-phase flows. However, accurate measurements require either intrusive or complex techniques. This paper reports on the Three Pressure Transducers (3PT) technique, which derives the speed of sound by measuring pressure fluctuations and which, thanks to its robustness and simplicity, could be applicable in harsh conditions. Therefore, the aim of this paper is to study in detail the feasibility of this technique against its limits and constraints in a cavitating flow. First, a numerical assessment of the technique is proposed to determine both the optimal transducers configuration and the sampling frequency. Then, the implemented algorithm was applied to a two-phase air-water mixture with well-known properties. Finally, the 3PT algorithm was used to study the behaviour of a cavitating flow induced by an orifice. This last application highlighted the possibility to use this technique to characterize the bubble flow generated by an orifice without the use of any optical access and by using a very compact experimental arrangement. The results obtained are also qualitatively compared to the images of the flow simultaneously acquired by a high-speed camera.