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逆壁射流中射流剪切层内湍流结构特性的实验研究

EXPERIMENTAL STUDY ON THE TURUBLENTCE STRUCTURE CHARACTERISES OF THE JET SHEAR LAYER IN A COUNTERFLOWING WALL JET

  • 摘要: 采用粒子图像测速技术对逆壁射流全流场进行了实验测量, 射流与主流的速度比为 8.89 , 基于射流圆管内径的雷诺数为9127. 主要关注射流剪切层内不同流向位置湍流的统计特性变化, 包括尺度特性和结构特性. 对射流中心线上不同流向位置的脉动速度场统计分析发现: 在 x/D = 30\sim 43 , 受反馈机制影响, Q1和Q4事件占据主导地位. 在驻点附近( x/D = 43\sim 50 )的区域Q3事件为主导事件. 对射流剪切层内湍流结构的平均空间尺度进行分析, 在 x/D = 0\sim 37 总尺度向射流下游发展呈增长趋势, 在 x/D = 37\sim 46 总尺度几乎不变, x/D = 46\sim 51 总尺度向射流下游发展呈减小趋势. 在 x/D = 35 之前, 参考点上游尺度与下游尺度近似. 在 x/D = 35\sim 41 , 参考点下游尺度大于上游尺度. 在 x/D = 41\sim 51 , 参考点下游尺度小于上游尺度. 利用频域上的本征正交分解方法对湍流结构进行了定量分析, 发现模态能量集中在低频, 流场中能量最大的模态频率为fD/U_j = 0.000\;5, 出现在再循环区. 频率为fD/U_j = 0.002\;6的第一阶模态说明射流发生偏转时与主流相互作用产生了湍流结构, 并且沿再循环区外围输运. 高频结构的构型是类似的, 均位于射流剪切层内, 且频率越高, 越接近射流出口, 尺度越小.

     

    Abstract: The experimental measurement of the flow field of counterflowing wall jet using the particle image velocimetry. The jet velocity ratio to the main flow velocity is 8.89, and the Reynolds number based on the jet pipe is 9127. This paper focuses on the statistical characteristics of turbulence at different streamwise positions in the jet shear layer, including scale characteristics and structural characteristics. Statistical analysis of the fluctuating velocity field at different streamwise direction positions on the jet centerline shows that: in the range of x/D = 30\sim43 , Q1 and Q4 events dominate due to the feedback mechanism. Q3 event is dominant in the region near the stagnation point ( x/D = 43\text \sim50 ). The spatial scale of the turbulent structure in the jet shear layer is analyzed. The total scale in the interval x/D = 0\sim37 shows an increasing trend downstream, and it is almost unchanged in the interval x/D = 37\sim46 . The total scale in the interval x/D = 46\sim 51 tends to decrease downstream. In the interval x/D = 0\sim35 , the upstream scale of the reference point is similar to the downstream scale. In the interval x/D = 35\sim41 , the downstream scale of the reference point is larger than the upstream scale. In the interval x/D = 41\sim51 , the downstream scale of the reference point is smaller than the upstream scale. The spectral proper orthogonal decomposition is used to quantitatively analyzes the turbulent structure. It shows that the energy of the mode is concentrated in low frequency. The most energetic mode in the flow field has a frequency offD/U_j = 0.000\;5 and appears in the recirculation region. The first mode with a frequency equal tofD/U_j = 0.002\;6 indicates that the turbulent structure is generated when the jet is deflected by the interaction with the main flow, and transported along the periphery of the recirculation region. The configurations of high-frequency structures are similar, all located in the jet shear layer, and the higher the frequency, the closer to the jet outlet, the smaller the scale.

     

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