Characteristics of flow pulsation of air ventilated submerged suspension jet and design optimization of ventilation nozzle head

2020 Fiscal Year Final Research Report

• Project/Area Number: 17K06169
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Fluid engineering
• Research Institution: Nihon University
• Principal Investigator: PENG Guoyi 日本大学, 工学部, 教授 (90295527)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: ウォータージェット / 混相流 / 流れの可視化 / 流動制御 / キャビテーション / アブレシブサスペンションジェット / 水中切断

Outline of Final Research Achievements

High-speed abrasive suspension jet (hereafter ASJ) shows a peculiar processing property but it decreases quickly under submerged condition. Aimed to establish an effective method for submerged cutting, high-speed video observation on the flow structure of air ventilated jets was carried out and a ventilation nozzle system to generate air coated jet in submerged condition has been developed. Air coated jets pulsate periodically, and the dominant frequency of jet pulsation decreases with the increase of ventilation flowrate. Strouhal number st defined by the dominant frequency depends upon an altered cavitation number σ_(sh) defined by the pressure in sheath. When σ_(sh)=0.0005 at an appropriate ventilation flowrate, stable cavities of 20~30d in length covering the jet are formed. Cutting tests show that the relative kerf of submerged cutting reaches to nearly one within this range of standoff distance and an equal processing ability of the cutting in air is demonstrated.

Free Research Field

流体工学

Academic Significance and Societal Importance of the Research Achievements

本研究は，流れの能動的制御の観点から，連続気層被覆水中ジェットを生成するノズルシステムを開発し，水中ジェットへの流体抵抗を大幅に低減する手法を提示した．その応用として，通気水中ASJを用いた水中切断工法を確立し，気中と同程度の切断能力を有することが検証された．福島第一原発など原子炉の解体作業に水中切断工法との重要な選択肢を示し，社会的意義は大きい．