Intermittent event evaluation through a multifractal approach for variable density jets
Intermittent event evaluation through a multifractal approach for variable density jets
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通过多重分形方法评估变密度射流的间歇事件
DOI：
10.1016/j.chaos.2021.110799
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Cal, Raúl Bayoán
中科院分区：
文献类型：
--
作者：
Viggiano, Bianca;Sakradse, Greg;Smith, Sarah;Mungin, Rihana;Ramasubramanian, Pradeep;Ringle, Dan;Travis, Kristin;Ali, Naseem;Solovitz, Stephen;Cal, Raúl Bayoán
变密度射流出现在许多系统中，包括地球物理流动和工业应用，表现出大范围的雷诺数和理查森数的尺度。一系列不同密度的射流垂直喷射到一个大的周围区域。利用粒子图像测速技术对氦气、空气和氩气三种不同气体的近出口速度场进行了测量。实验认为相对较低的雷诺数约为1500至5500与理查森数接近0.001的幅度。这些包括各种流动响应，特别是近层流，湍流和过渡射流。通过多重分形框架研究流动，奇异性谱显示了基于流向和壁面法线方向演化的流动特征。Hölder指数的变化反映了流动的不对称性和不稳定性。与雷诺剪应力类似，间歇行为的发展是下游位置相对于雷诺数变化的函数。离开射流的密度也影响流量信号内的高不稳定性的位置。较低密度的射流在环境空气和靠近射流出口的剪切层内提供增加的信号变化性。具体而言，在过渡雷诺数的氦射流的混合层内观察到最高程度的多重分形。相对于波动的速度分量和逐点Hölder指数的条件平均揭示了高的速度-不稳定性的相互作用，在内部的射流混合层时，流体被夹带和在湍流/非湍流界面时，流体被喷射。最后，线积分卷积说明了湍流/非湍流界面对射流动力学的影响。
Variable-density jets occur in many systems, including geophysical flows and industrial applications, exhibiting a large range of scales of Reynolds and Richardson numbers. A series of jets with varying densities was ejected vertically into a large ambient region. Using particle image velocimetry, the near-exit velocity fields were measured for three different gases exhausting into air: helium, air and argon. Experiments considered relatively low Reynolds numbers from approximately 1500 to 5500 with Richardson numbers near 0.001 in magnitude. These included a variety of flow responses, notably nearly laminar, turbulent and transitioning jet flows. Flows were examined through a multifractal framework, and the singularity spectrum showed the characteristics of the flow based on the evolution in the streamwise and wall-normal direction. The variation of the Hölder exponent displayed the asymmetry and intermittency of the flow. Similar to the Reynolds shear stress, the development of intermittent behavior is a function of downstream location with respect to changes in the Reynolds number. The density of the exiting jet also influences the location of high intermittency within the flow signal. Lower density jets provide increased variability of the signal within the ambient air and the shear layer close to the exit of the jet. Specifically, the highest degree of multifractality is observed within the mixing layer of the helium jet at a transitioning Reynolds number. Conditional averaging with respect to the fluctuating velocity components and the pointwise Hölder exponent reveals high velocity-intermittency interactions at the inside of the jet mixing layer when fluid is entrained and at the turbulent/non-turbulent interface when fluid is ejected. Finally, line integral convolution illustrates the impact of turbulent/non-turbulent interface on the jet dynamics.
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影响因子：
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作者：
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