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Unsteady large-scale flow patterns and dynamic vortex movement in near- field triple buoyant plumes

机译:近场三重浮羽中的不稳定大尺度流动模式和动态涡旋运动

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Unsteady flow patterns of interacting buoyant plumes are important for buoyant ventilation and particularly influence pollutant and heat transports in indoor and outdoor environments. This study reveals fundamental large-scale flow patterns in triple building plumes, investigates vortex moving trends during the pattern transition processes, and explores possible mechanisms of pattern diversity by two-dimensional (2-D) Particle Image Velocimetry (PIV). Total five tests are studied, including three different heat strengthsQ(180, 90, and 30 W) and three source layouts characterized by the ratios of source spacingSto source widthW(0.2, 0.5, and 1.0).Streamline distributions and axial velocity profiles clearly reveal three fundamental global flow patterns: a right-slanting asymmetrical flow pattern, a left-slanting asymmetrical flow pattern, and an axisymmetric flow pattern. Correspondingly, it indicates four basic transition processes, i.e., right-to-center, left-to-center, center-to-right, and center-to-left transitions (“center” represents the axisymmetric pattern). A novel vortex tracking method, based on lambda-2 (λ2) criterion and principles of the PIV technique, is developed and successfully applied to qualitatively track the vortex moving trends during the transition processes. The regular vortex moving trends are found to be reasonably consistent with the global pattern transition trends.The flow pattern diversity is speculated to be mainly driven by unstable heat source wall flows and downstream swaying motions in this study. These critical unstable motions are considered to probably relate to unstable lateral entrainment and vortex interaction, particularly beside the central plume. Consistently, the regular vortex moving trends are usually observed in and around the central plume.
机译:相互作用的浮羽的不稳定流动模式对于浮力通风非常重要,尤其会影响室内外环境中的污染物和热传递。这项研究揭示了三层建筑羽流中的基本大规模流动模式,研究了模式转变过程中的涡旋运动趋势,并通过二维(2-D)粒子图像测速技术(PIV)探索了模式多样性的可能机制。共进行了五项测试,包括三种不同的热强度Q(180、90和30 W)以及三种以源间距与源宽度W(0.2、0.5和1.0)之比为特征的源布局,流线分布和轴向速度曲线清楚地显示了三个基本整体流动模式:右倾斜的不对称流动模式,左倾斜的不对称流动模式和轴对称的流动模式。相应地,它指示四个基本过渡过程,即,从右到中心,从左到中心,从中心到右和从中心到左的过渡(“中心”表示轴对称模式)。提出了一种基于lambda-2(λ2)准则和PIV技术原理的新型涡旋跟踪方法,并成功应用于定性跟踪过渡过程中涡旋运动趋势。研究发现,规则的涡旋运动趋势与总体模式转变趋势合理地一致。在本研究中,流型多样性被认为主要是由不稳定的热源壁流和下游的摇摆运动驱动的。这些关键的不稳定运动被认为可能与不稳定的横向夹带和涡旋相互作用有关,特别是在中心羽流附近。一致地,通常在中央羽流中和周围观察到规则的涡旋运动趋势。

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