The impact of heating the breakdown bubble on the global mode of a swirling jet: Experiments and linear stability analysis
The impact of heating the breakdown bubble on the global mode of a swirling jet: Experiments and linear stability analysis
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DOI：
10.1063/1.4963274
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发表时间：
2016-05
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影响因子：
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通讯作者：
Lothar Rukes;M. Sieber;Oliver Paschereit;K. Oberleithner
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文献类型：
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作者：
Lothar Rukes;M. Sieber;Oliver Paschereit;K. Oberleithner
本文研究了非等温旋转射流发生涡破裂时的动力学行为，重点研究了螺旋拟序结构。提出了加热回流泡可以抑制主要的螺旋相干结构。这一命题进行了评估与立体粒子图像测速（PIV）测量的击穿区的等温和加热的旋转射流。通过PIV快照，通过本征正交分解，获得了主导螺旋结构的相干动能。对于一组实验参数，温和的加热被发现，以增加占主导地位的螺旋模式的能量含量。强加热导致相干结构能量减少30%。对于第二组实验参数，检测不到主导相干结构的改变。时均速度场的局部线性稳定性分析表明，两种配置之间的关键差异是各自造波器位置的密度比。发现约0.8的密度比与实验中的全局模式的抑制相关。模型的密度和速度分布的参数研究表明，最重要的参数，支配当地的绝对增长率：密度比和相对位置的密度分布和内部剪切层。
This study investigates the dynamics of non-isothermal swirling jets undergoing vortex breakdown, with an emphasis on helical coherent structures. It is proposed that the dominant helical coherent structure can be suppressed by heating the recirculation bubble. This proposition is assessed with Stereo Particle Image Velocimetry (PIV) measurements of the breakdown region of isothermal and heated swirling jets. The coherent kinetic energy of the dominant helical structure was derived from PIV snapshots via Proper Orthogonal Decomposition. For one set of experimental parameters, mild heating is found to increase the energy content of the dominant helical mode. Strong heating leads to a reduction by 30\% of the coherent structures energy. For a second set of experimental parameters, no alteration of the dominant coherent structure is detectable. Local linear stability analysis of the time-averaged velocity fields shows that the key difference between the two configurations is the density ratio at the respective wavemaker location. A density ratio of approximately 0.8 is found to correlate to a suppression of the global mode in the experiments. A parametric study with model density and velocity profiles indicates the most important parameters that govern the local absolute growth rate: The density ratio and the relative position of the density profiles and the inner shear layer.