立管群绕流与尾流致振的旋涡脱落机理研究

Multiple riser system is widely applied on offshore engineering, especially on the exploration of deep-sea oil and gas fields. However, the multiple risers could be easily damaged due to mutual collision and wake induced vibration (WIV). Therefore, more and more attentions have been paid on the flow behavior behind multiple tubes and the phenomenon of wake induced vibration. In this study, to study the generation mechanism of the wave induced vibration phenomenon, a series of experiments will be carried out in the water channel with the adoption of particle image velocimetry (PIV) technique, to investigate the flow characteristics behind multiple tubes. Moreover, numerical simulations for flow past multiple tubes in terms of Computational Fluid Dynamics (CFD) approach are also going to be conducted to investigate the wake characteristics under the condition with or without oscillations. In this study, instantaneous and time-averaged wake patterns of velocity, streamline topology, vorticity and normalized Reynolds stress contours behind the multiple tubes at different arrangements, spacing ratios and Reynolds numbers will be analyzed. The effects of gap ratio and Reynolds number on oscillation amplitude, vortex shedding frequency and flow patterns will be examined. For multiple side-by-side tubes, instantaneous wake patterns will be investigated to provide a plausible interpretation for the generation mechanism of gap flow deflection. In addition, the occurrence condition, period, and influence of Reynolds number for the gap flow deflection phenomenon will also be investigated. For multiple tandem tubes, special attention will be paid on the occurrence of bi-stable regimes. It is believed that this study will be of significant benefit to the understanding of the generation mechanism of the wake-induced vibration phenomenon for multiple riser system, and therefore the design of multiple risers and their disaster protection in the oil and gas upstream industry.

多管体绕流与尾流致振作为海洋立管群系统疲劳破坏的主要诱因，在深海油气开采中日益受到关注。本项目拟通过物理模型试验与数值模拟相结合的方法开展多管体系统绕流与尾流致振过程中旋涡脱落的机理研究，研究内容包括：利用粒子图像测速技术采集多管体系统绕流与尾流致振过程中的流场信息，同时运用计算流体力学方法建立数学模型获取流场特征及结构动力响应。在不同管体间距、来流方向和雷诺数条件下，分析多管体绕流和尾流致振过程中的瞬时及时均速度矢量、流线拓扑、涡量等值线及雷诺应力等值线；探讨多管体尾流旋涡脱落形态、结构动力响应随管体间距、来流方向和雷诺数的变化规律；确定不同旋涡脱落形态发生的临界间距；从可视化角度阐明多管体间隙流交替偏斜现象发生的瞬时速度、频率及其与雷诺数之间的关系；揭示双稳态流现象的产生机制。研究成果可为深水油气开采中立管群系统的设计、防护及优化布局提供技术依据，具有重要的科学意义和应用价值。

多管体系统作为深海油气开采中海洋立管及锚系系统普遍采用的一种结构型式，极易在波、浪、流及海上浮式生产储油船FPSO 受迫牵连振动共同作用下发生相互碰撞或诱发尾流致振导致破坏，在深海油气开采中备受关注。本项目主要采用粒子图像测速（PIV）技术和计算流体力学（CFD）方法开展了一系列立管群绕流与尾流致振流场的物理模型试验及数值研究，获得了不同工况下的多管体绕流流场信息，揭示了多柱体系统尾流旋涡脱落形态、旋涡脱落频率随布置方式、间距比及雷诺数变化的规律；开展了悬挂柱体涡激振动和旋转柱体受迫振动的可视化试验研究，揭示了悬挂柱体结构动力响应及尾流结构形态如运动轨迹、振动幅度、瞬时旋涡脱落形态、柱体的振动频率等随流速变化的规律，探讨了不同频率比条件下旋转柱体受迫振动流场旋涡脱落形态；同时建立了双柱体、方形布置四柱体绕流及尾流致振流场的数学模型，研究了多柱体系统尾流致振发生时结构动力响应特性，探讨了柱体间尾流致振动的作用机理。本课题的研究对于深入研究柱体绕流与涡激振动特性，具有一定的理论意义，并可为海洋立管管群的设计及防护等问题的研究奠定理论和技术基础。..发表标注本基金的资助论文13篇，其中SCI收录论文6篇，参加国际学术交流2人次，国内学术交流13人次，获得浙江省科学技术进步奖三等奖1项，出版专著1本。2017年毕业硕士生1名，1名硕士生即将在2018年3月毕业。