Active Control of Heat and Mass Transfer using Functional Jets Array

控制标量输运和局部分布对于改进喷射式流体装置具有重要意义。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)和两个平行的平面冲击水射流(宽度10 mm，喷嘴间距36 mm，雷诺数500-1000)。为了利用粒子图像测速仪(PIV)设计控制系统，对速度场特性进行了研究。在第一种方法中，根据热线探头阵列实时检测到的速度分布，采用反馈控制来确定三种射流的出口速度。随着扰动恢复时间的缩短，平均速度分布的脉动强度减小，系统变得健壮。将神经网络算法应用于进一步复杂的速度或浓度分布形状的控制。在第二种方法中，通过实验研究了射流混合与周围射流速度之比之间的关系，实现了以时序控制的方式实现浓度分布定向旋转的控制系统。在第三种方法中，通过喷嘴出口处的细缝通过合成激励来操纵局部剪切层，以控制碰撞板附近的涡量。该反馈控制系统通过改变涡流来改变激励方式和相位，从而减小了壁温波动。

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.