水下重力流的临界弗雷德数的实验研究
发布时间：2018-08-24 12:29
【摘要】：传统一般认为水下重力流和明渠流一样存在着急流、缓流,并且将密度弗雷德数或理查德森数是否为1作为临界值来判定重力流的流态。直到最近有根据断面比能的理论分析研究提出水下重力流的临界密度弗雷德数可以不为1或不存在,取决于重力流对环境流体的夹带程度与其所携带的沉积物与底床的物质交换。目前还没有完整的实验数据支持此项结论。本研究通过一个带3°坡度转换的水槽盐水流实验,在斜坡及坡道转换处使用声学多普勒测速仪(ADV)测量出其速度;采用尾部补水及加挡板来控制尾流回流的影响,使用虹吸管及电导率仪测量出其浓度,进而算出各剖面处的深度平均速度、深度平均浓度、重力流厚度、密度弗雷德数、理查德森数、动能修正系数、断面比能等,以验证该理论分析的正确与否。经过8次重力流实验,得到具体分析结果如下:对于水下重力流来说,密度弗雷德数在很大程度上失去了传统弗雷德数对于明渠流的意义,实验重力流的临界弗雷德数值为0.49,验证了此前考虑到了流量及浓度变化的根据断面比能的理论分析。尽管实验密度弗雷德数在实验重力流的全流域小于1,但综合根据深度平均速度、重力流厚度的观察在坡道转换处有一明显的突变,特别是根据其和明渠流完全不同的断面比能的观察,重力流在坡道转换处的5 m~5.5 m区域其断面比能随着水深的增加而降低,满足传统的明渠流的急流定义,而在其它区域其断面比能随着重力流厚度的增加而增加,可以推测其在坡道转换处还是发生了一个较弱的水跃。
[Abstract]:It is generally believed that there are jet and slow flow in underwater gravity flow as well as open channel flow, and whether the density of Fred number or Richardson number is 1 is taken as the critical value to determine the flow state of gravity flow. Until recently, it was proposed that the critical density Fred number of underwater gravity flow could not be 1 or non-existent according to the theoretical analysis of specific energy of the section. It depends on the degree of entrainment of environmental fluid by gravity flow and the exchange of material between sediment and bed carried by gravity flow. There is no complete experimental data to support this conclusion. In this study, the velocity was measured by using acoustic Doppler velocimetry (ADV) at the slope and ramp transition through a flume brine flow experiment with 3 掳slope conversion, and the influence of wake reflux was controlled by tail filling water and adding baffle. The concentration was measured by siphon and conductivity meter, and then the depth average velocity, depth average concentration, gravity flow thickness, density Fred number, Richardson number, kinetic energy correction coefficient, section specific energy and so on were calculated. To verify the correctness of the theoretical analysis. After eight experiments of gravity flow, the results are as follows: for underwater gravity flow, the density Fred number loses the significance of traditional Fred number for open channel flow to a great extent. The critical Fred value of the experimental gravity flow is 0.49, which verifies the theoretical analysis based on the cross section specific energy, which considered the change of flow rate and concentration. Although the experimental density Fred number is less than 1 in the whole basin of the experimental gravity flow, according to the depth average velocity, the observation of gravity flow thickness has an obvious abrupt change at the ramp transition. In particular, according to the observation of the cross-section specific energy which is completely different from that of the open channel flow, the specific energy of the gravity flow in the 5m ~ 5.5 m area of the ramp transition decreases with the increase of the water depth, which satisfies the traditional definition of the open channel flow. However, in other regions, the specific energy of the cross section increases with the increase of gravity flow thickness, so it can be inferred that there is a weak water jump at the ramp transition.
【学位授予单位】：安徽工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV131
本文编号：2200824
[Abstract]:It is generally believed that there are jet and slow flow in underwater gravity flow as well as open channel flow, and whether the density of Fred number or Richardson number is 1 is taken as the critical value to determine the flow state of gravity flow. Until recently, it was proposed that the critical density Fred number of underwater gravity flow could not be 1 or non-existent according to the theoretical analysis of specific energy of the section. It depends on the degree of entrainment of environmental fluid by gravity flow and the exchange of material between sediment and bed carried by gravity flow. There is no complete experimental data to support this conclusion. In this study, the velocity was measured by using acoustic Doppler velocimetry (ADV) at the slope and ramp transition through a flume brine flow experiment with 3 掳slope conversion, and the influence of wake reflux was controlled by tail filling water and adding baffle. The concentration was measured by siphon and conductivity meter, and then the depth average velocity, depth average concentration, gravity flow thickness, density Fred number, Richardson number, kinetic energy correction coefficient, section specific energy and so on were calculated. To verify the correctness of the theoretical analysis. After eight experiments of gravity flow, the results are as follows: for underwater gravity flow, the density Fred number loses the significance of traditional Fred number for open channel flow to a great extent. The critical Fred value of the experimental gravity flow is 0.49, which verifies the theoretical analysis based on the cross section specific energy, which considered the change of flow rate and concentration. Although the experimental density Fred number is less than 1 in the whole basin of the experimental gravity flow, according to the depth average velocity, the observation of gravity flow thickness has an obvious abrupt change at the ramp transition. In particular, according to the observation of the cross-section specific energy which is completely different from that of the open channel flow, the specific energy of the gravity flow in the 5m ~ 5.5 m area of the ramp transition decreases with the increase of the water depth, which satisfies the traditional definition of the open channel flow. However, in other regions, the specific energy of the cross section increases with the increase of gravity flow thickness, so it can be inferred that there is a weak water jump at the ramp transition.
【学位授予单位】：安徽工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV131
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