Abstract—

The excitation of pressure fluctuations in a model jet-driven Helmholtz oscillator is experimentally investigated. An axisymmetric channel consisted of a cylindrical chamber with a nozzle in the front cover and an outlet opening in the back one. Optimal geometric dimensions of the chamber, nozzle, and outlet were chosen to achieve the greatest amplitude of the pressure fluctuations in the chamber. The nozzle length-to-diameter ratio l_n/d_n varied in the 0.77 ≤ l_n/d_n ≤ 4.17 range. The cylindrical chamber length L_ch determining the air jet length l_jet in the interval between the covers and L_ch/d_n = 0.5–3.5. The outlet opening diameter in the back cover d_out varied within the limits d_out/d_n = 1–2.5. The optimal nozzle length l_n/d_n, the corresponding chamber length L_ch/d_n, and the outlet diameter d_out/d_n are determined. The air jet development within the nozzle and the formation of an inverse flow zone between the nozzle wall and the jet periphery and a chain of vortex structures in the mixing layer are considered. The generation of a jet tone of the opening on the frequency of the feedback in the jet and a family of acoustic modes on the resonance frequency with a smooth increase in the jet velocity from 0 to 70 m/s is studied.

中文翻译：

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喷嘴长度对射流驱动亥姆霍兹振荡器性能的影响

摘要-

实验研究了模型喷气驱动的亥姆霍兹振荡器中压力波动的激发。轴对称通道由一个圆柱形腔室组成，该腔室的前盖中有一个喷嘴，后盖中有一个出口。选择腔室，喷嘴和出口的最佳几何尺寸，以实现腔室内压力波动的最大幅度。喷嘴长度与直径的比率升_ñ / d _Ñ在0.77≤改变升_ñ / d _Ñ ≤4.17范围内。圆柱腔室长度L _ch确定在盖和L之间的间隔中的空气喷射长度l _jetch / d _n = 0.5-3.5。后盖的出口开口直径d _out在极限d _out / d _n = 1-2.5之间变化。最佳喷嘴长度l _n / d _n，相应的腔室长度L _ch / d _n和出口直径d _out / d _n确定。考虑了喷嘴内的空气喷射发展以及在喷嘴壁和喷嘴外围之间形成逆流区以及混合层中的涡旋结构链。研究了在喷射速度从0到70 m / s平稳增加的情况下，在喷射的反馈频率上产生开口的喷射音和在共振频率上产生一系列声学模式的现象。