Basic Study on Active-Feedback Control of Non-Linear Heat and Fluid Flow

为了寻求一种有效的热量和流体流动的主动反馈控制方法，人们对控制理论和控制装置进行了广泛的研究。得到了以下结论：将次优控制理论应用于数值模拟的槽道流动，以展向虚体力场作为控制输入。与简单的反馈控制相比，次优控制可以在较小的控制量下实现显著的湍流减阻效果。采用直接数值模拟方法，对柔性壁湍流通道中壁面变形的简单振荡模式进行了实验研究。在平均流动特性以及瞬时流动结构中观察到实质性的影响。结果表明，湍流结构在增强相和阻尼相都依赖于壁面变形的尺度，基于神经网络的最优控制算法可以有效地控制热传导和Burgers方程。该方法还成功地应用于圆柱下游速度脉动的控制。为了控制近壁面准流向涡结构的运动，设计了12组襟翼作动器阵列。研究了电磁襟翼作动器的周期性运动对湍流统计特性的影响，发现作动器的周期性运动选择性地影响展向速度分量。模型预测的襟翼动态特性与实验结果吻合较好。在圆形喷嘴唇缘上安装一组襟翼可以显著地操纵轴对称射流的旋涡脱落现象。通过一系列的DNS和实验室实验研究了壁湍流中颗粒的动力学行为。研究了颗粒对传热现象的影响。

In pursuit of an effective active feedback control methodology for heat and fluid flow, control theories and control devices were studied extensively. The following conclusions can be derived :A suboptimal control theory is applied to the numarically-simulated channel flow with a spanwise virtual body force field as a control input. The suboptimal control achieves a significant turbulent drag reduction with fairly small control, when compared with simple feedback law.A simple oscillatory mode of wall deformation is tested in a turbulent channel with a flexible wall by using direct numerical simulation. The substantial influences are observed in the mean flow properties as well as instantaneous flow structures. The turbulent structures are found to be dependent on the scales of the wall deformation at both their enhanced and damped phases.The optimal control algorithm based on neural network (NN) was found to be effective for controlling the heat conduction and the Burgers equations. The present method is also applied to the management of velocity fluctuations downstream of a cylinder successfully.An array of twelve sets of flap actuators was developed so as to control the kinematics of the near-wall quasi-streamwise vortical structures. The effect of periodic motion of the actuators on the turbulent statistics was found to affect the spanwise velocity component selectively.A prototype electromagnetic flap actuator was developed with photo lithography. The dynamic characteristics of the flap predicted by models were in reasonable agreement with experimental results. A group of flap mounted on the circular nozzle lip can manipulate significantly the vortex shedding phenomena of an axisymmetric jet.Dynamics of particles in wall turbulence was examined by using a series of DNS and laboratory experiments. The effect of particle on heat transfer phenomena was also studied.