Pinch-off process of underwater annular-nozzled gas jet

doi:10.11949/j.issn.0438-1157.20170666

Abstract

Abstract:

An experimental study was carried out on basic phenomena, pinch-off characteristics and penetration depth of underwater gas jet ejecting out of a vertical annular nozzle. The process of gas jet development was recorded by a high-speed camera, and jet interfaces were tracked by processing pictures with an edge detection algorithm. The pinch-off spatial distribution was determined by summation of downstream position across all recorded times. The gas jet penetration distance was calculated by counting transient pixel values divided by measured time duration of gas observed for all pixel locations. The color contour was used to indicate time percentage for gas to occupy a certain location in the field of view. The results show that underwater annular-nozzled gas jets exhibit two stages of continuous jet and centralized pinch-off. More pinch-off occurs near nozzle and less pinch-off occurs further away from nozzle in the study conditions. Pinch-off frequency at momentum jet section for all nozzles is reduced with the increase of gas flow rate. Back-attack phenomenon upon pinch-off is the result of axial obstruction and transverse expansion of subsequent gas instead of gas flowing backwards and impinging on nozzle end. The jet penetration distance is proportional to gas flow rate for ring seams of same sizes.

Key words: underwater gas jet, pinch-off, back-attack, penetration depth

摘要：

对水下竖直环形喷管出口气体射流现象进行了研究，采用高速摄影仪记录了水下气体射流发展过程，并通过MATLAB编程处理图片的方式，对夹断的判定、夹断的位置和频率做了探讨，对环形喷管射流的特性进行了分析。结果表明：环形喷管水下气体射流呈现出持续射流和集中夹断两种阶段；在本文工况下，水下气体射流离喷口越近，夹断次数越多，离喷口越远，夹断次数越少；对于本文所有喷管，其动量射流段发生夹断的频率都随气体流量增加而减小；水下气体射流的回击现象并不是气体反向倒流撞击喷管端面形成的，而是夹断发生后，后续喷入的气体在轴向受阻，进而横向扩张的结果；对于环缝大小一定的喷管，气体流量越大，射流穿透深度越大。

关键词: 水下气体射流, 夹断, 回击, 穿透深度

CLC Number:

O359⁺.1

LI Tingting, HU Jun, CAO Xuejie, YU Yong. Pinch-off process of underwater annular-nozzled gas jet[J]. CIESC Journal, 2017, 68(12): 4565-4575.

李婷婷, 胡俊, 曹雪洁, 于勇. 环形喷管水下气体射流夹断过程[J]. 化工学报, 2017, 68(12): 4565-4575.

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