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

本研究项目涉及加热和未加热非圆形湍流单射流和同轴射流的实验研究，这些射流可能是受限的或非受限的。喷射是一种流动，如烟囱排出的污水、飞机发动机排出的废气、进入燃烧室的气流等，它们从喷嘴和孔口发出。当其中一个喷嘴或孔包围另一个时，就形成了同轴射流。无约束射流是指向几乎无界的环境中喷射的射流，而有约束射流是指被壁包围的射流。当气流参数雷诺数（即驱动气流的力与阻碍气流的力之比）超过临界值时，射流就被称为湍流。根据喷嘴或孔板出口形状的不同，可以区分圆形和非圆形射流。喷射流体与周围流体混合的速率可以对以下方面产生重要影响：例如，烟囱排出的污染物在环境中的扩散、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。清楚地了解喷射混合现象将有助于控制上述技术上重要的过程，从而使发生这些过程的设备的性能得到改善。射流混合可以主动增强（即通过施加在流动上的时间扰动）或被动增强（即通过改变喷嘴或孔板的几何形状）。非圆形射流，无论是单射流还是同轴射流，都有望成为被动增强混合的有效途径。因此，本文的研究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，促进对非圆形射流混合现象的基本理解，第二，提供实验数据，可用于促进这些流动的数值计算湍流建模。

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.