【摘要】：傳統(tǒng)一般認(rèn)為水下重力流和明渠流一樣存在著急流、緩流,并且將密度弗雷德數(shù)或理查德森數(shù)是否為1作為臨界值來判定重力流的流態(tài)。直到最近有根據(jù)斷面比能的理論分析研究提出水下重力流的臨界密度弗雷德數(shù)可以不為1或不存在,取決于重力流對環(huán)境流體的夾帶程度與其所攜帶的沉積物與底床的物質(zhì)交換。目前還沒有完整的實驗數(shù)據(jù)支持此項結(jié)論。本研究通過一個帶3°坡度轉(zhuǎn)換的水槽鹽水流實驗,在斜坡及坡道轉(zhuǎn)換處使用聲學(xué)多普勒測速儀(ADV)測量出其速度;采用尾部補(bǔ)水及加擋板來控制尾流回流的影響,使用虹吸管及電導(dǎo)率儀測量出其濃度,進(jìn)而算出各剖面處的深度平均速度、深度平均濃度、重力流厚度、密度弗雷德數(shù)、理查德森數(shù)、動能修正系數(shù)、斷面比能等,以驗證該理論分析的正確與否。經(jīng)過8次重力流實驗,得到具體分析結(jié)果如下:對于水下重力流來說,密度弗雷德數(shù)在很大程度上失去了傳統(tǒng)弗雷德數(shù)對于明渠流的意義,實驗重力流的臨界弗雷德數(shù)值為0.49,驗證了此前考慮到了流量及濃度變化的根據(jù)斷面比能的理論分析。盡管實驗密度弗雷德數(shù)在實驗重力流的全流域小于1,但綜合根據(jù)深度平均速度、重力流厚度的觀察在坡道轉(zhuǎn)換處有一明顯的突變,特別是根據(jù)其和明渠流完全不同的斷面比能的觀察,重力流在坡道轉(zhuǎn)換處的5 m~5.5 m區(qū)域其斷面比能隨著水深的增加而降低,滿足傳統(tǒng)的明渠流的急流定義,而在其它區(qū)域其斷面比能隨著重力流厚度的增加而增加,可以推測其在坡道轉(zhuǎn)換處還是發(fā)生了一個較弱的水躍。
[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 擄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.
【學(xué)位授予單位】：安徽工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TV131

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本文編號：2200824