Abstract This paper focuses on the effects of a space-time dependent periodic stirring of a moderately turbulent planar co-flow jet configuration. The baseline flow is agitated in time and in space by small-scale turbulent perturbations in combination with large-scale modulation imposed at the inflow plane of a rectangular domain of size L × L × 2L in the x, y and z directions respectively. The prescribed large-scale modulation is characterized by a single modulation frequency ω and modulation wave-number, K. A parametric study at different modulation frequencies and wave-numbers is performed. We evaluate the system response to the external agitation in terms of key dynamic properties of the flow, e.g., the total kinetic energy ET, the global averaged dissipation rate and additional flow mixing properties. For low modulation frequencies, e.g., ω = 0.5 ω 0 , where ω0 is the large scale-turn over frequency, ω 0 = U 1 / D , with U1 and D being relevant velocity and length scales, and at given wave-number K, we observe that ET follows the imposed oscillation with a periodic amplitude response that is sustained at locations further from the inflow plane, whereas for higher frequencies, the response amplitude rapidly decays. Results of the global dissipation rate show the development of a definite maximum value of the response amplitude at frequencies on the order of ω0 for any modulation wave-number K. To investigate in more detail the effects of modulated turbulence on the jet mixing properties, a passive scalar was injected at the inflow plane. The spreading of the scalar surface in the agitated jet was monitored for a wide range of modulation frequencies. In general, results show enhanced mixing efficiency when the main jet is modulated at frequencies near ω0 and low K values.

中文翻译：

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并流射流中湍流的时空调制

摘要 本文重点研究了中等湍流平面协流射流构型的时空相关周期性搅拌的影响。基线流动在时间和空间上通过小尺度湍流扰动与在 x、y 和 z 方向分别施加在大小为 L × L × 2L 的矩形域的流入平面上的大规模调制相结合。规定的大规模调制的特点是单一的调制频率 ω 和调制波数 K。在不同的调制频率和波数下进行参数研究。我们根据流动的关键动态特性评估系统对外部搅动的响应，例如总动能 ET、全球平均耗散率和额外的流动混合特性。对于低调制频率，例如，ω = 0.5 ω 0 ，其中 ω0 是大尺度翻转频率，ω 0 = U 1 / D ，U1 和 D 是相关的速度和长度尺度，在给定的波数 K 下，我们观察到 ET 遵循施加具有周期性振幅响应的振荡，该振荡在离流入平面较远的位置持续，而对于较高频率，响应振幅迅速衰减。全局耗散率的结果表明，对于任何调制波数 K，在 ω0 数量级的频率处响应幅度的确定最大值的发展。 为了更详细地研究调制湍流对射流混合特性的影响，一个在流入平面注入被动标量。在很宽的调制频率范围内，对搅动射流中标量表面的扩散进行了监测。一般来说，