Development of Intelligent Jet Nozzle

为了追求单喷嘴产生多种射流模式的可能性，在喷嘴出口唇上安装了一排微型电磁襟翼作动器，对轴对称和同轴射流进行扰动。电磁襟翼作动器采用光刻技术制作，由提供的控制信号独立驱动。利用平面激光诱导荧光（PLIF）技术和定量速度测量技术，研究了低雷诺数下受控射流的时空流动结构。对于轴对称自由射流，证明了襟翼致动器在射流剪切层中引入的各种扰动可以改变大尺度涡结构的形成和演化过程。特别是，当襟翼致动器的每半簇被驱动180度时，射流明显地分成两个分支。最有效的扑动斯特罗哈尔数几乎是恒定的，为0.25。在这种控制模式下，交替倾斜的涡之间相互作用，相继产生了远离射流轴的涡环。对于密闭同轴水射流，外射流与周围流体之间剪切层的卷升与襟翼产生的人为扰动同步，显著改变了大尺度涡旋结构的演化。在射流出口附近也观察到强烈的逆流。为了评价目前的控制方案在流动混合和燃烧方面的效果，将几乎相同的设置应用于同轴空气射流。当St=0.9接近首选模态频率时，轴对称襟翼运动能最有效地增强内外流体的混合。对主动燃烧控制也作了初步的尝试。在最佳的扑动频率下，利用轴对称扑动来稳定升力火焰。

In pursuing a possibility of producing various jet flow modes with a single nozzle, axisymmetric and coaxial jets is perturbed by a row of miniature electromagnetic flap actuators equipped on the nozzle exit lip. The electromagnetic flap actuators are fabricated by photolithography so as to be independently driven by control signals supplied. The spatio-temporal flow structures of the controlled jet at a relatively low Reynolds number are studied through flow visualization using planer laser-induced fluorescence (PLIF) and quantitative velocity measurement.For axisymmetric free jet, it is demonstrated that various disturbances introduced in the jet shear layer by the flap actuators can modify the process of formation and evolution of large-scale vortical structures. In particular, when each half cluster of the flap actuators are driven 180 degree out of phase, the jet bifurcates clearly into two branches. The most effective Strouhal number of flapping, is nearly constant and 0.25. In this control mode, the vortex rings successively produced turn away from the jet axis by the mutual interaction between alternatively inclined vortices.For confined coaxial water jet, the roll-up of the shear layer between the outer jet and the ambient fluid is synchronized with the artificial disturbances generated by the flaps, and the evolution of large scale vortical structures are modified significantly. Strong reverse flow is also observed near the jet exit. Almost the same setup is applied to coaxial air jet in order to evaluate the present control scheme in flow mixing and combustion. Mixing between the inner and outer fluid was enhanced most effectively by the axisymmetric flap motion at St=0.9, which is close to the preferred mode frequency. Preliminary attempt was also made for active combustion control. A lifted flame was stabilized by the axisymmetric flap motion at the optimum flapping frequency for mixing.