Development of Intelligent Jet Nozzle

为了探索用单喷管产生多种射流模式的可能性，在喷管出口唇缘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。电磁襟翼致动器通过光刻制造，以便由所提供的控制信号独立地驱动。通过平面激光诱导荧光（PLIF）流动显示和速度定量测量，研究了较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，襟翼激励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.特别地，当襟翼致动器的每个半簇被驱动180度异相时，射流明显地分叉成两个分支。最有效的Strouhal扑翼数，几乎是恒定的和0.25。在这种控制模式下，通过交替倾斜的涡之间的相互作用，相继产生的涡环逐渐远离射流轴线，对于同轴受限射流，外部射流与周围流体之间剪切层的卷起与襟翼产生的人工扰动同步，大尺度涡结构的演化得到显著改善。在射流出口附近也观察到强烈的反向流动。几乎相同的设置适用于同轴空气射流，以评估目前的控制方案在流动混合和燃烧。在St=0.9时，轴对称襟翼运动最有效地增强了内部和外部流体之间的混合，这接近于优选模式频率。并对主动燃烧控制进行了初步尝试。在最佳扑翼频率下，通过轴对称扑翼运动稳定提升火焰以实现混合。

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.