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The manipulation of large- and small-scale flow structures in single and coaxial jets using synthetic jet actuators.

机译:使用合成射流致动器在单轴和同轴射流中操纵大型和小型流动结构。

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Control of the mixing of fuel and oxidizer in a combustor is necessary for high combustion efficiency, combustor stability, and low emissions. The traditional approach to control of mixing in free shear flows has been indirect, relying on manipulation of large-scale, global instability modes of the base flow upstream of mixing transition. The control influence is transferred to the scales at which molecular mixing occurs by means of the classical cascading mechanism. More efficient control of mixing in fully turbulent shear flows might be achieved by direct control of both the large-scale entrainment and small-scale mixing processes. The present work focuses on mixing control based on concurrent manipulation of both the small- and large-scale dynamical processes via direct long-range couplings between large- and small-scale motions in axisymmetric jets.; Single and coaxial round jets are instrumented with an azimuthal array of nine synthetic jet actuators placed near the jet exit plane around the nozzle circumference. The synthetic jets operate at high frequency (nominally 1200 Hz), resulting in direct excitation of the small-scales of the primary flow. Results are presented for a single jet (ReD = 1.9 × 104) and coaxial jets (Ai/Ao = 0.5 and Ui/Uo = 0.35, 0.65, and 1.4 for which the Reynolds number based on uniform volume flow rate is ReDH = 7.6 × 10 3). The present work shows that axisymmetric, high-frequency forcing leads to increases in rms velocity fluctuations and jet spreading in the near field (x/D 1). When the excitation waveform is amplitude modulated with all actuators in phase, the small-scale motions are advected within nominally axisymmetric large-scale vortical structures. In the single jet, these structures propagate along the jet axis and lead to temporal modification of the global entrainment of ambient fluid. In the coaxial jet, these structures are strongest when Ui/Uo 1, leading to significant interaction between the two fluid streams. Manipulation of the geometry of the jet cross section is achieved through non-axisymmetric forcing patterns.
机译:为了实现高燃烧效率,燃烧器稳定性和低排放,必须控制燃烧器中燃料和氧化剂的混合。控制自由剪切流中混合的传统方法是间接的,它依赖于混合过渡上游基流的大规模,全局不稳定性模式的操纵。通过经典的级联机制,控制影响转移到发生分子混合的尺度。通过直接控制大规模夹带过程和小规模混合过程,可以实现更有效地控制全湍流剪切流中的混合。目前的工作集中在混合控制的基础上,该混合控制是通过轴对称射流中大型运动和小型运动之间的直接远程耦合直接对小型和大型动力学过程进行并发操纵的。单个和同轴圆形喷嘴装有9个合成喷嘴致动器的方位角阵列,该阵列放置在喷嘴周围喷嘴周围的喷嘴出口平面附近。合成射流以高频率(标称值为1200 Hz)运行,从而直接激发了小流量的主流。给出了单喷嘴(Re D = 1.9×10 4 )和同轴喷嘴(A i / A o < / sub> = 0.5且U i / U o = 0.35、0.65和1.4,基于均匀体积流量的雷诺数为Re DH < / sub> = 7.6×10 3 )。目前的工作表明,轴对称的高频强迫导致均方根速度波动的增加和近场射流扩展(x / D &lsim; 1)。当激励波形在所有执行器同相的情况下进行幅度调制时,小规模运动会在名义上轴对称的大尺度涡旋结构内平流。在单股射流中,这些结构沿射流轴传播,并导致环境流体整体夹带的时间变化。在同轴射流中,当U i / U o <1时,这些结构最强,从而导致两种流体流之间发生显着的相互作用。射流横截面的几何形状的操纵是通过非轴对称的强制模式实现的。

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