Transient positively and negatively buoyant turbulent round jets
Transient positively and negatively buoyant turbulent round jets
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DOI：
10.1007/s003480050336
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发表时间：
1999
影响因子：
2.4
通讯作者：
L. Pantzlaff;Richard M. Lueptow
中科院分区：
文献类型：
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作者：
L. Pantzlaff;Richard M. Lueptow
采用流动显示和PIV技术，通过改变射流雷诺数和流体密度比，测量了不同密度弗劳德数条件下，垂直圆柱形容器底部中心位置向上的喷嘴喷射到不同密度液体中的瞬态特性。正浮力射流穿透自由表面，由向上方向的动量和浮力驱动。较轻的喷射流体在大量液体上方分层。在启动时，负浮力射流具有三个阶段。首先，射流穿透到水箱中的最大高度。然后，由于射流周围较重的流体向下回流，从而减小了射流的向上动量，从而减小了射流穿透。射流穿透高度在最大穿透高度的70%左右波动。对于较小的负弗劳德数，流动是喷泉状的。向下的流动在到达罐的底部时径向向外转向，并且最终在罐的底部处形成环形再循环区，其具有与射流的涡度相反的涡度运动。对于较大的负弗劳德数，射流的扩散延伸得足够远，使得环形向下流沿着罐壁，从而产生较大的环形再循环区。穿透深度h和时间t与浮力通量F和射流动量通量M成比例，ashM-3/4 <$F <$1/2andt <$F <$/M可将正浮力射流或负浮力射流的瞬态射流穿透高度数据压缩到一条弗劳德数范围较宽的单一曲线上。
The transient character of the jet issuing from an upward nozzle centered at the bottom of a vertical cylindrical tank into bulk liquid of a different density was measured using flow visualization and PIV for varying densimetric Froude numbers by varying the jet Reynolds numbers and the ratios of fluid densities. Positively buoyant jets penetrate to the free surface, driven by both momentum and buoyancy in the upward direction. The lighter jet fluid stratifies in a layer above the bulk liquid. Upon starting, a negatively buoyant jet has three stages. First the jet penetrates to its maximum height in the tank. Then the jet penetration decreases due to the downward backflow of heavier fluid surrounding the jet, which reduces the jet’s upward momentum. Finally the jet penetration height fluctuates around a mean value about 70% the maximum height of penetration. For small negative Froude numbers, the flow is fountain-like. The downward flow turns radially outward as it reaches the bottom of the tank and eventually an annular recirculation zone forms at the bottom of the tank with vortical motion opposite the vorticity of the jet. For large negative Froude numbers, the spreading of the jet extends far enough so the annular downward flow is along the walls of the tank resulting in a large annular recirculation zone. The penetration depth,h, and time,t, scale with buoyancy flux,F, and the jet momentum flux,M, ashM-3/4∣F∣1/2andt∣F∣/Mto collapse the transient jet penetration height data onto a single curve over a wide range of Froude numbers for either positively or negatively buoyant jets.