对称突扩水流流态失稳和流场结构

对称突扩分离再附水流现象广泛存在于工程和生活中，流道突扩易产生局部水头损失、压力变化、结构振动、次生噪声等，对称突扩存在流场对称性失稳现象，如管道对称突扩等。然而，由于紊流的复杂性和量测技术的局限性，人们对其流动特性和流态演变规律认识仍然不足，有必要开展对称突扩流动的流场结构分析研究。本文基于物理模型试验和高精度图像粒子测速技术，模拟了不同雷诺数条件下（Re=539~48 911）对称突扩水流流动现象和精细流场结构，包含层流、过渡流和充分发展的紊流典型流态，随着雷诺数Re增加，流态从层流过渡到紊流，从对称到非对称分布，其流态发生对称性失稳，高雷诺数紊流时主流偏向一侧，流场结构相对稳定；揭示了突扩水流主流两侧形成的非对称分布的大尺度涡漩结构，其与流场对称性失稳有关联。

Asymmetric flow pattern and flow structure ofa symmetric enlarged step flow

Symmetric enlarged step flow with a separation and reattachment process exists widely in engineering and life.Enlarged flow boundary easily produces local head loss, pressure change, structural vibration, secondary noise, etc.Symmetric enlarged flow has an asymmetric phenomenon flow field, such as pipe symmetric enlarged flow.However, Due to the complexity of turbulent flow and the limitation of measurement technology, it''s still difficult for people to understand the complex turbulent phenomena and kinematic evolution.So, it''s necessary to investigate the flow structure of the symmetric enlarged flow.Based on physical model tests and high precision particle image velocimetry measurements, this study tries to simulate typical flow phenomenon and fine velocity structure for a symmetry enlarged step flow, containing flow patterns of laminar, transition and fully developed turbulence with flow conditions of Reynolds number (Re=539~48911).As the increase of Reynolds number, flow pattern changes from laminar to turbulent, with flow structure transition from symmetry to asymmetric distribution.For higher Reynolds number turbulent flow, the main flow develops in one direction or the other, while the flow field structure is relatively stable.The large scale vortex structure with asymmetric distribution formed on both sides of the main flow is revealed, which is related to the asymmetric flow field.