Mixing in non-circular single and coaxial jets with and without confinement

本研究计划涉及加热和未加热的非圆形湍流单轴和同轴射流的实验研究，这些射流可以是受限的或无限制的。 射流是流动，例如来自烟囱的排出物、来自飞机发动机的排气、进入燃烧室的流动等，其从喷嘴和孔口发出。当喷嘴或孔中的一个围绕另一个时，形成同轴射流。 无约束射流是指实际上进入无限环境的射流，而有约束射流是指被壁包围的射流。 当超过称为雷诺数的流动参数的临界值（雷诺数是驱动流动的力与阻碍流动的力的比率）时，射流被称为湍流。 根据喷嘴或孔出口形状，在圆形和非圆形射流之间进行区分。喷射流体与周围流体混合的速率可以对例如来自烟囱的污染物流出物在环境中的分散、喷气式飞机的噪声产生以及飞机或汽车发动机中燃料和空气的混合具有重要影响。 对射流混合现象的清楚理解将有助于控制上述技术上重要的过程，从而能够改进发生这些过程的装置的性能。 射流混合可以主动地（即，通过施加在流上的时间扰动）或被动地（即，通过改变喷嘴或孔几何形状）。非圆形射流，无论是单一的和同轴的，显示出作为被动增强混合的有效方式的希望。因此，本研究的重点是研究非圆形单射流和同轴射流中的射流混合现象。 该计划有两个主要目标：第一，有助于在非圆形射流的射流混合现象的基本理解，第二，提供实验数据，可用于促进湍流模型的数值计算这些流量。

This research program involves the experimental investigation of heated and unheated non-circular turbulent single and coaxial jets which may be confined or unconfined.  Jets are flows, such as the effluent from a chimney stack, the exhaust from an aircraft engine, flow into a combustion chamber, etc., which emanate from nozzles and orifices. When one of the nozzles or orifices surrounds the other, a coaxial jet is formed.  Unconfined jets are those which issue into practically unbounded surroundings, while confined jets are those which are surrounded by walls.  Jets are referred to as turbulent when the critical value of a flow parameter known as the Reynolds number, which is the ratio of the forces that drive the flow to those that retard it, is exceeded in them.  One differentiates, depending upon the nozzle or orifice exit shape, between circular and non-circular jets. The rate at which the jet fluid mixes with the surrounding fluid can have important effects on, for example, the dispersion of pollutant effluents from chimney stacks in the environment, the generation of noise by jet aircraft, and the mixing of fuel and air in an aircraft or automobile engine.  A clear understanding of the phenomenon of jet mixing will facilitate the control of the aforementioned technologically important processes and thus enable the performance improvement of the devices in which they occur.  Jet mixing can be enhanced either actively (i.e., through disturbances in time imposed on the flow) or passively (i.e., through changes in the nozzle or orifice geometry). Non-circular jets, both single and coaxial, show promise as an effective way of enhancing mixing passively. The present research is, therefore, focussed on studying the phenomenon of jet mixing in non-circular single and coaxial jet flows.  The program has two principal objectives: first, to contribute to the fundamental understanding of the phenomenon of jet mixing in non-circular jets, and second, to provide experimental data which can be used to facilitate turbulence modelling for the numerical computation of these flows.