借助于阵列式微型制动器控制同轴喷嘴实现起升火焰的稳定燃烧

Active control of a lifted flame is investigated using a coaxial nozzle with magnetic flap actuators arranged on the inner periphery of the annular nozzle. Near-field vortical structures of the methane/air coaxial jet are manipulated by introducing disturbances directly to the initial shear layer. Through the manipulation, we can improve flame stability and flexibly control the liftoff height. It is found that the large-scale vortical structures play a dominant role in the flame stabilization, and its spatio-temporal evolution is examined with the aid of PIV and LIF to elucidate the control mechanism. By introducing flap motion driven with a saw-wave signal, we can force the outer shear layer to roll up into strong vortices in synchronization with the flaps. When the flapping Strouhal number is unity, the lifted flame is anchored at x/Do ~ 1.5. The strong vortices induced by the flaps produce a blob of flammable mixture, which has velocity smaller than the flame speed. The possible stabilization mechanism is that the time period of the premixture supply is balanced with the consumption time of the premixture at the flame base. On the other hand, when the jet is manipulated by a square-wave signal, the lifted flame is located stably at x/Do ~ 4, which is downstream of the inner potential core. It is found that vortical structures in the shear layers break into turbulence close to the nozzle exit. The possible mechanism of the flame stabilization is that the flame propagating upstream is undisturbed due to the absence of intermittent passage of large-scale vortices.