Experimental study on bow flow field of scientific research ship based on flow visualisation

Abstract To investigate the bubble sweep-down phenomenon of a scientific research ship from the perspective of its flow mechanism, the flow-field characteristics of the bow were measured in a towing-tank environment. First, the silk-thread method was used to visualise the streamline characteristics of the bow. Next, the flow field of the bow was measured using multiple two-section 2-dimensional computed tomography scans with stereoscopic particle image velocimetry. The flow-field information of different sections at different speeds (e.g., velocity distribution, vector characteristics, and streamline distribution) were then obtained. A 3-dimensional (3D) three-component (3C) space reconstruction of the time-averaged flow field in the bow was thus realised. From the visualisation results, the flow field in the bow generally exhibits a downward movement trend. The flow structure of the bow flow field was found to be closely related to the wave-making change of the bow. On the other hand, the cross-sectional flow characteristics and 3D reconstruction results showed that with the bubble sweep-down, some bubbles flowed along the bilge and amassed with other bubbles, breaking through the geometric inflection point of the bilge. Compressed by the bilge vortex, they slid backward and affected the operation of acoustic equipment.