完全单向（层流）流动很少见。可以通过覆盖整个天花板的高效空气过滤器或在供气（层流）扩散器阵列周围放置限制板来尝试这种气流。在大多数其他情况下，气流是“半单向的”——仅在送风气流的核心是单向的，在其他位置是再循环/混合的。本研究分析了等温和非等温条件下这种半单向流动的行为。开发了一个虚拟试验箱的CFD模型，以研究送风量/排风量对气流模式、速度和温度分布的影响。分析了总共四个供应气流速率，范围从200 cfm（94.4 lps）到800 cfm（377.6 lps）。对两个不同的显热源位置进行了非等温分析- 一个热源在桌子上，另一个热源在天花板附近。这项研究表明，在等温条件下，排气速度（流速）对供气射流的流动行为几乎没有影响。在分析的条件下，等温向下空气射流的速度在距离排气口约60%的距离后降低（并变得非单向）。然而，在非等温条件下，放电速度会显著影响流动的方向性。当在工作台上放置热源时，当送风喷嘴的冷却能力是冷却负荷的四倍时，空气喷嘴可以克服热空气向上的浮力。当热源放置在天花板附近时，热源周围的热空气夹带到向下移动的射流中，导致中心线速度加速，这表明随着气流速率的增加而减小。 有趣的是，对于最低的送风量，这种加速度是最低的。这项研究进一步表明，在非等温条件下，阿基米德数可以作为一个很好的初始指标来估计供气射流的方向性。该数值应小于0.2，以便冷空气射流在不显著丧失其单向性能的情况下进一步移动。引文:2018年冬季会议，伊利诺伊州芝加哥，会议论文

Perfectly unidirectional (laminar) flows are rare. Such flows can be attempted either by supplying the air through HEPA filters covering the entire ceiling or by placing restraining panels around the array of supply (laminar) diffusers. In most other cases the flows are "semi unidirectional" - unidirectional only in the core of the supply air stream and recirculating/mixing in the other locations. This study analyzes behavior of such semi unidirectional flows under isothermal and non-isothermal conditions. A CFD model of a virtual test chamber is developed to study the effect of supply airflow rates/discharge velocity on the airflow patterns, velocity, and temperature distribution. A total of four supply airflow rates ranging from 200 cfm (94.4 lps) to 800 cfm (377.6 lps) are analyzed. Non-isothermal analyses are performed for two different locations of sensible heat sources - one with the heat source on a table and the other with heat sources near the ceiling. This study indicates that under isothermal conditions the discharge velocity (flow rate) has little impact on the flow behavior of the supply air jet. For the conditions analyzed, the velocity of the isothermal downward air jet decreases (and becomes non-unidirectional) after traveling about 60 percent of the distance from the discharge. However, in the case of non-isothermal conditions the discharge velocity can significantly affect the directionality of the flow. When a heat source was placed on the table and when the cooling capacity of the supply air jet was four times the cooling load, the air jet could overcome the upward buoyant force of the hot air. When heat sources were placed near the ceiling, the hot air surrounding the heat sources entrained into the downward moving jet causing acceleration in the centerline velocity, which showed to decrease with increasing airflow rate. Interestingly such acceleration was lowest for the lowest supply airflow rate. This study further indicates that for non-isothermal conditions Archimedes Number can be a good initial indicator for estimating the directionality of the supply air jet. This number should be smaller than 0.2 for the cold air jet to travel further without substantially losing its unidirectional behavior.