Active Control of Heat and Mass Transfer using Functional Jets Array

标量输运和局部分布的控制对射流利用流体装置的改进具有重要意义。为了控制热流体特性，引入了射流阵列和反馈控制的概念。在本研究中，研究了三种类型的射流阵列，即三个平行的二维空气射流阵列（宽度15 mm，喷嘴间距50 mm，雷诺数4000-8000），交错排列的七个圆形空气射流（直径13 mm，喷嘴间距17 mm，雷诺数1700-9500）和两个平行平面冲击水射流（宽度10 mm，喷嘴间距36 mm，雷诺数500-1000）。利用粒子图像测速技术（PIV）对流场特性进行了研究，为控制系统的设计提供了依据。第一种方法是利用热线探针阵列真实的实时测量射流的速度分布，通过反馈控制确定三股射流的出口速度。减小了平均速度分布的波动强度，缩短了系统对扰动的恢复时间，增强了系统的鲁棒性。神经网络算法被用来进一步复杂的速度或浓度分布的形状作为控制器。第二种是通过实验研究射流混合与周围射流速度比之间的关系，从而实现了控制系统的定向形状，它可以旋转浓度分布的方向作为一个时序控制。在第三个，操纵的局部剪切层通过合成激励通过细缝在喷嘴出口处施加，以控制附近的冲击板的涡。本反馈控制系统表明，壁温波动的减少，通过修改涡改变图案和相位的激励。

Control of scalar transport and local distribution is of significance for improvement of jet utilized fluid devices. Concepts of an array of jets and feedback control were introduced in order to control thermal fluid features. In the present study, three types of array of jets were investigated, that is, an array of triple parallel 2-dimensional air jets (width 15mm, nozzle spacing 50mm and Reynolds number 4000-8000), a staggered array of seven circular air jets (diameter 13mm, nozzle spacing 17mm and Reynolds number 1700-9500) and two parallel planar impinging water jets (width 10mm, nozzle spacing 36mm and Reynolds number 500-1000). Characteristics of the velocity field were examined in order to design control system by particle image velocimetry (PIV). In the first one, the exits velocity of the three jets were determined with feedback control based on the velocity distribution detected by an array of hot-wire probes in real time. Fluctuation intensity of the averaged velocity distribution was reduced and the system became robust with the recovering time shortened for disturbance. Neural network algorithm was applied to further complicated shape of velocity or concentration profile as a controller. In the second one, the relation between jets mixing and the ratio of the surrounding jets velocity was examined experimentally so that control system to realize the directional shape was achieved, which can rotate the orientation of concentration profile as a time sequential control. In the third one, manipulation of the local shear layers via the synthetic excitation through the fine slits at the nozzle exit was applied in order to control vorticies near the impinging plate. The present feedback control system showed the reduction of wall temperature fluctuation by the modification of vortices changing the pattern and the phase of the excitation.