Research on Turbulent Mixing Phenomena in T-junctions and Development of Efficient Method for Mixing Control

本文对方形截面T形管中的湍流混合进行了实验研究，并根据测量结果提出了一种有效的促进和控制方法。我们已经测试了两种类型的混合T型接头。一种是逆流型T形接头，其中主流和分支流在T形接头中迎面碰撞，并且混合流体沿以直角连接到主通道和分支通道的混合通道向下流动。另一种是交叉流型T型接头，其分支与主通道成直角连接，在逆流型T型接头中，采用高空间/时间分辨率的PIV和PLIF同时测量，研究了混合后的速度场和浓度场的详细特性：在主通道流体中溶解了罗丹明6 G作为荧光示踪剂。分析了速度场的三维特征及其对速度场的影响 ...更多信息 澄清了混合流中的浓度场。研究发现，混合通道内形成二次流，高浓度流体沿横向输送。通过POD分析，混合层在展向方向的摆动运动和主通道流的合理运动已被提取从瞬时场。在横流式T型接头中，主通道的冷流与分支的热流在T型接头处汇合，在T型接头处，主通道的冷流与分支通道的热流在T型接头处汇合，在T型接头处，主通道的冷流与分支通道的热流在T型接头处汇合。分别用PIV和热电偶耙测量了流场结构和平均温度分布。此外，热混合层中的湍流热通量已被测量的LDV和冷丝温度计相结合。在T型接头后的主通道中观察到一个大的分离泡，在其周围的剪切层中产生了强烈的湍流，但这种强烈的湍流出现在热混合层以下，对冷热流的湍流热混合没有有效的贡献。基于这些实验结果，我们提出了混合促进和控制的方法与小射流吹到主通道的T形接头的上游边缘在45 °方向上的主流。这些射流可以增加热混合层上部的湍流强度，从而有效地促进冷热气流的湍流混合。此外，热混合的程度可以通过改变射流速度来控制。少

Experimental studies have been conducted on the turbulent mixing in T-junctions with square cross sections and, based on the results of measurements, an effective method of its promotion and control has been developed. We have tested two types of mixing T-junctions. One is the counter-flow type T-junction in which the main and branch flows collide head-on in the T-junction and the mixed fluid flows down the mixing channel that is connected to the main and branch channels at right angles. The other is the cross-flow type T-junction, in which the branch is connected to the main channel at right angles.In the counter-flow type T-junction, detailed characteristics of the velocity and concentration fields after the mixing have been investigated using simultaneous measurements by PIV and PLIF with high spatial/time resolutions : Rhodamine 6G has been dissolved in the main-channel fluid as fluorescence tracer. The three-dimensional characteristics of the velocity field and its influence on th … More e concentration field in the mixed flow were clarified. It has been found that the secondary flows are formed in the mixing channel and the high-concentration fluid is transported in the transverse direction. By POD analysis, the wobbling motion of the mixing layer in the spanwise direction, and a rational motion of the main-channel flow have been extracted from instantaneous fields. Moreover, the mechanism of turbulent mixing of two fluids has been analyzed based on the turbulent mass fluxes.In the cross-flow type T-junction, the cold flow in the main channel and the hot flow in the branch merge in the T-junction. The flow structure and the mean temperature distributions have been measured by PIV and the thermocouple rake, respectively. Moreover, the turbulent heat fluxes in the thermal mixing layer have been measured by combining LDV and a cold-wire thermometer. A large separation bubble is observed in the main channel after the T-junction and strong turbulence is generated in the shear layer around it. This strong turbulence, however, appears below the thermal mixing layer, thus it does not contribute effectively to the turbulent thermal mixing of hot and cold flows. Based on these experimental results, we have proposed the mixing promotion and controlling method with small jets that are blown into the main channel at the upstream edge of the T-junction in the direction of 45 degrees against the main flow. Turbulence intensity in the upper part of the thermal mixing layer can be increased with these jets, and consequently the turbulent mixing of hot and cold airflows is promoted effectively. Moreover, the degree of thermal mixing can be controlled by changing the jet velocity. Less