Active Control of Heat and Mass Transfer using Functional Jets Array

控制标量输运和局部分布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，即三平行二维空气射流阵列（宽度15mm，喷嘴间距50mm，雷诺数4000-8000），七个圆形空气射流交错阵列（直径13mm，喷嘴间距17mm，雷诺数1700-9500）和两个平行平面冲击水射流阵列（宽度10mm，喷嘴间距36mm，雷诺数500-1000）。利用粒子图像测速法（PIV）对速度场特性进行了研究，为控制系统的设计奠定了基础。在第一种方法中，基于一组热线探头实时检测到的速度分布，采用反馈控制方法确定三束射流的出口速度；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。将神经网络算法应用于进一步复杂形状的速度或浓度剖面作为控制器。第二，通过实验研究了射流混合与周围射流速度比的关系，实现了定向形状的控制系统，该控制系统可以作为时间序列控制来旋转浓度剖面的方向。在第三种方法中，通过喷嘴出口细缝处的合成激励来操纵局部剪切层，以控制撞击板附近的涡度。该反馈控制系统通过改变涡的形状和激励的相位来减小壁面温度波动。

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.