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

这项研究计划涉及对加热和不加热的非圆形湍流单轴和同轴射流的实验研究，这些射流可能是受限的，也可能是无受限的。这些射流是从喷嘴和孔口发出的流动，如烟囱的流出物、飞机发动机的废气、流入燃烧室的气体等。当一个喷嘴或孔口围绕着另一个喷嘴或孔口时，就形成了同轴射流。无限制射流是那些射入几乎没有边界的环境中的射流，而受限射流是那些被墙壁包围的射流。当一个被称为雷诺数的流动参数的临界值被超过时，这些射流被称为湍流。雷诺数是推动流动的力量与阻碍流动的力量的比率，当这些流动参数的临界值超过时，就会形成同轴射流。根据喷嘴或孔口出口形状的不同，圆形和非圆形射流是不同的。喷射流体与周围流体的混合速度可能对环境中烟囱排出的污染物的扩散、喷气式飞机产生的噪音以及飞机或汽车发动机中燃料和空气的混合产生重要影响。清楚地了解喷射混合现象将有助于控制上述重要的技术过程，从而能够改进发生这些混合的设备的性能。可以主动(即，通过对流动施加的时间扰动)或被动(即，通过改变喷嘴或孔口几何形状)来增强喷射混合。非圆射流，无论是单轴的还是同轴的，都被认为是一种有效的被动强化混合的方法。因此，本研究的重点是研究非圆形单轴和同轴射流中的射流混合现象。该程序有两个主要目标：第一，有助于从根本上理解非圆形射流中的射流混合现象，第二，为这些流动的数值计算提供可用于湍流模拟的实验数据。

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.