Distribution characteristics of spanwise vortex of vortex wave field in channel flow
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摘要:
通过2DPIV测量了槽道内涡波流场的瞬态速度矢量场，利用雷诺分解和旋转强度的
λ ci准则进行了展向涡的识别；并从识别的逆时针和顺时针展向涡的尺度属性、力学属性和运动属性方面分析了展向涡的分布特征。结果表明，流场中的顺时针展向涡的数量大于逆时针展向涡的数量；在法向位置0.05~0.45范围内，逆时针展向涡的旋转强度呈抛物线形状变化，顺时针展向涡整体呈下降趋势；逆时针展向涡的平均直径和椭圆平均长轴长度随着法向位置的增加而缓慢增加，而顺时针展向涡趋于下降；逆时针展向涡的椭圆长轴倾角最大值为67.28°，顺时针展向涡的等效椭圆的离心率呈下降趋势，似圆性较好；逆时针展向涡对全局平均的〈vω z 〉分量在法向位置0.15处出现最大值61%；展向涡对流场雷诺应力的影响较小；逆时针展向涡的数量密度在0~0.08法向位置范围内呈急剧上升趋势，并达到最大值0.36，顺时针展向涡数量密度整体呈倒U形分布；不同旋向的展向涡占总展向涡数量密度的比值都大于0.3；展向涡的流向对流速度整体上小于流场的平均速度，且在槽道中心区域差值较大；展向涡的法向对流速度随着法向距离增加，从负值上升到正值，在中心主流两侧分别发生喷射和扫掠2种现象。Abstract:The instantaneous velocity vector fields of the vortex wave field in the channel flow were measured by 2DPIV. The identification of the spanwise vortices is carried out by using the criteria of Reynolds decomposition and swirling strength
λ ci criteria. The distribution characteristics of spanwise vortices are analyzed from scale properties, mechanical properties and motion properties of the counter-clockwise and clockwise vortices identified by swirling strengthλ ci criteria. The results show that the number of clockwise vortices is larger than that of the counter-clockwise vortices in the flow field. The swirling strength of the counter-clockwise vortices is in the form of parabolic shape in the range of normal direction 0.05-0.45, while the clockwise vortices show the overall downward trend. And the average diameter and the long axis of the ellipse of the counter-clockwise vortices increase slowly with the increase of the normal position, while the clockwise vortex tends to decrease. The largest value of the inclination angle of the long axis of the ellipse of the counter-clockwise spanwise vortices is 67.28°. The eccentricity of the equivalent ellipse of the clockwise vortices shows a decreasing trend, and the circularity is better. The contribution of the counter-clockwise spanwise vortices to the total mean 〈vω z 〉 has a maximum value of 61% at normal direction 0.15, and the contribution of the spanwise vortices to the total Reynolds stress is smaller; the population densities of counter-clockwise spanwise vortices in the 0-0.08 normal displacement range have a sharp upward trend, and achieve the maximum 0.36; The distribution of the clockwise spanwise vortices shows the inverted "U"-shape; The population density ratio of spanwise vortices with different directions of swirling to total spanwise vortices is greater than 0.3; the streamwise convective velocity of the spanwise vortices is less than that of the mean velocity of flow field in general, and the difference between them is larger in the central region of the channel. The normal convective velocity of the spanwise vortex increases from negative value to positive value with the increase of normal distance, and two phenomena of ejecting and sweeping occur on the two sides of the central mainstream.-
Key words:
- channel /
- vortex wave field /
- spanwise vortex /
- identification of vortex /
- distribution characteristics
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图 2 涡波流场的展向涡λci准则识别结果
Figure 2. Identification results of spanwise vortex λci criteria in vortex wave field
图 3 展向涡的平均直径和平均长轴长度
Figure 3. Mean diameter and mean length of long axis of spanwise vortex
图 4 展向涡的长轴倾角和离心率
Figure 4. Long axis inclination angle and eccentricity of spanwise vortex
图 6 展向涡对的〈vωz〉分量和雷诺应力分量
Figure 6. 〈vωz〉 component and Reynolds stress component of spanwise vortex pair
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