本研究使用數值模擬方法，分析一凸出壁面圓形噴流，受到橫風衝擊時近尾流區流場的結構，及污染物質在此流場之擴散情形。其中噴流對橫風之動量比定義為R，R為流場特徵量。本文固定橫風，藉由改變噴流速度使R由小至大，分析不同模態的流場。本研究流場主要可以分為四種模態：下洗模態、橫流支配模態、過渡模態以及噴流支配模態。當動量比小於0.2以下，在噴流管內前緣處，可以明顯觀察到盤旋渦漩(hovering vortex)的形成。隨著動量比增大，較大動量的垂直噴流促使盤旋渦漩消失。
在污染物質擴散方面，經由濃度場的分析，本研究發現R主導噴流物質的擴散效應。當R由小增大，整體濃度擴散範圍由噴流管口下方流場，抬升到噴流管口上方的區域；影響濃度擴散的機制主要由橫風與噴流間的交互作用引導。噴流因橫風衝擊而形成對轉渦漩對(counter-rotating vortex pair, CVP)，其產生捲增效應(entrainment effect)大量混合噴流與週遭橫風流體，成為橫風與噴流衝擊區域上最主要的濃度擴散機制。

Flow patterns and variations of pollutant concentration induced by a jet coming
from a vertical round tube in a crossflow are numerically simulated in this study.Various flow patterns with respect to the momentum ratio R of jet to cross wind are investigated. There are four characteristic modes in the predicted flows, i.e.downwash, crossflow-dominated, transition and jet-dominated. A hovering vortex is observed in the vicinity of the exit of the round tube when R is less than 0.2. It shrinks due to a growing vertical jet when R increases. Furthermore, it is found that R dominates the concentration variation in the jet via the analysis of concentration fields. Pollutants are downwashed when R is less than 0.5, but pollutants are only found in the region above the exit of the round tube. A pair of counter-rotating vortices are found in the cross section of a jet in a cross flow. Those vortices induce the entrainment effect which mixes up fluids in jet and cross flow. It becomes the main mechanism of pollutant diffusion in the flow.

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