【摘要】：階梯-深潭系統(tǒng)是山區(qū)河流常見的河床結(jié)構(gòu),具有穩(wěn)定河床和消能減災(zāi)的作用。本研究以階梯-深潭系統(tǒng)為研究對象,在對天然河流發(fā)育階梯-深潭系統(tǒng)觀測基礎(chǔ)上,對階梯-深潭系統(tǒng)的結(jié)構(gòu)形態(tài)、水力特性和消能率展開研究,闡述了階梯-深潭系統(tǒng)水流能量轉(zhuǎn)化過程與消能機(jī)理,研究了推移質(zhì)運(yùn)動(dòng)對階梯-深潭系統(tǒng)消能的影響。通過對怒江、小江和雅魯藏布江階梯-深潭系統(tǒng)野外考察,將其按結(jié)構(gòu)形態(tài)分為3類:三維階梯-深潭、二維階梯-深潭和二維三維之間階梯-深潭,對各種形式結(jié)構(gòu)特點(diǎn)進(jìn)行總結(jié),推薦三維階梯-深潭作為典型階梯-深潭。二維、三維階梯-深潭系統(tǒng)消能對比試驗(yàn)驗(yàn)證了三維階梯-深潭具有更高消能率,且隨著流量增大二維階梯-深潭消能率迅速降低,三維階梯-深潭消能率降低緩慢,在高流量時(shí)仍能維持較高消能率。自然階梯-深潭系統(tǒng)具有高消能率,本試驗(yàn)工況消能率為64%-91%。階梯-深潭系統(tǒng)流場具有強(qiáng)三維性。階梯與深潭水力特性相差大,階梯上沿流向時(shí)均流速占主導(dǎo),紊動(dòng)弱;深潭中時(shí)均流速低,紊動(dòng)強(qiáng)度高。試驗(yàn)工況下,階梯上相對紊動(dòng)強(qiáng)度約0.1,深潭中則最大超過8.0。深潭中雷諾應(yīng)力是階梯上約50倍。推導(dǎo)得到的階梯-深潭消能率計(jì)算公式計(jì)算值與實(shí)測值符合較好。階梯-深潭系統(tǒng)消能分為階梯消能和深潭消能。水流能量轉(zhuǎn)化分為3個(gè)過程:從階梯跌落勢能轉(zhuǎn)化為時(shí)均動(dòng)能;進(jìn)入深潭時(shí)均動(dòng)能轉(zhuǎn)化為紊動(dòng)能;紊動(dòng)能耗散。由能譜和耗散譜分析知,水流進(jìn)入階梯-深潭后,能量由低頻向高頻轉(zhuǎn)移,隨著流量增大,深潭中紊動(dòng)強(qiáng)度增大,能量耗散率增強(qiáng),相比沒有河床結(jié)構(gòu)發(fā)育河段,階梯-深潭系統(tǒng)更劇烈的將時(shí)均動(dòng)能轉(zhuǎn)化為紊動(dòng)能,且具有更高耗散率。低流量時(shí),階梯消能占主導(dǎo),隨著流量增加,深潭消能作用逐漸增強(qiáng),使階梯-深潭始終保持高消能率,這是階梯-深潭系統(tǒng)不同于其他河床結(jié)構(gòu)的根本之處。山區(qū)河流能量消耗主要依靠推移質(zhì)運(yùn)動(dòng)消能和河床結(jié)構(gòu)消能。加沙試驗(yàn)顯示,推移質(zhì)運(yùn)動(dòng)的增強(qiáng)改變水流能量分配,其消能作用使階梯-深潭結(jié)構(gòu)消能降低,深潭於埋。推移質(zhì)運(yùn)動(dòng)使階梯上紊動(dòng)與耗散略為增強(qiáng),深潭中紊動(dòng)與耗散大為減弱,從而使階梯-深潭系統(tǒng)消能率降低。
[Abstract]:Ladder-deep pool system is a common river bed structure in mountainous area, which has the function of stabilizing river bed and reducing energy dissipation. Based on the observation of natural river development ladder deep pool system, the structure, hydraulic characteristics and energy dissipation rate of ladder deep pool system are studied in this paper. The energy transfer process and energy dissipation mechanism of stepped deep pool system are described. The effect of bed load motion on energy dissipation in stepped deep pool system is studied. Based on the field investigation of the Nu River, Xiaojiang River and Yalu Zangbo River stairs-deep pool system, they are divided into three categories according to their structure: three dimensional ladder deep pool, two dimensional ladder deep pool and two dimensional three dimensional ladder deep pool. This paper summarizes the characteristics of various forms of structure and recommends three-dimensional ladder-deep pool as a typical ladder-deep pool. The comparison test of energy dissipation in two dimensional and three dimensional ladder deep pool system proves that the three dimensional ladder deep pool has higher energy dissipation rate, and with the increase of flow rate, the energy dissipation ratio of two dimensional ladder deep pool decreases rapidly, and the energy dissipation rate of three dimensional ladder deep pool decreases slowly. High energy dissipation rate can be maintained at high flow rate. The natural ladder-deep pool system has high energy dissipation rate, and the energy dissipation rate in this test condition is 64-91. The flow field of the stepped-deep pool system is strongly three-dimensional. There is a big difference between the hydraulic characteristics of the ladder and the deep pool, the average velocity is dominant and the turbulence is weak, and the average velocity is low and the intensity of turbulence is high in the deep pool. Under the test conditions, the relative turbulence intensity on the ladder is about 0.1, and the maximum in the deep pool is more than 8.0. The Reynolds stress in the deep pool is about 50 times higher than that in the staircase. The calculated value of the energy dissipation rate formula derived from the step-deep pool is in good agreement with the measured value. Step-deep pool system energy dissipation is divided into step energy dissipation and deep pool energy dissipation. The energy conversion of water flow can be divided into three processes: from step drop potential energy to average kinetic energy, from average kinetic energy to turbulent energy when entering deep pool, and turbulent energy dissipation. According to the analysis of energy spectrum and dissipation spectrum, the energy transfer from low frequency to high frequency is obtained after the flow enters the staircase to deep pool. With the increase of flow rate, the turbulence intensity and energy dissipation rate in deep pool increase, compared with no river bed structure developed in river reach. The time-averaged kinetic energy is transformed into turbulent energy and the dissipation rate is higher in the stepped-deep pool system. With the increase of flow rate, the energy dissipation of deep pool is gradually enhanced, which makes the energy dissipation rate keep high, which is the fundamental point that the ladder-deep pool system is different from other river bed structure. The energy consumption of mountain rivers mainly depends on bed load motion energy dissipation and riverbed structure energy dissipation. The Gaza test shows that the enhancement of bed load movement changes the energy distribution of water flow, and its energy dissipation results in the decrease of energy dissipation of the stepped deep pool structure, and the deep pool is buried in the deep pool. The bed load motion increases the turbulence and dissipation slightly in the staircase, and weakens the turbulence and dissipation in the deep pool, thus reducing the energy dissipation rate of the stepped deep pool system.
【學(xué)位授予單位】：清華大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TV135.2

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本文編號(hào)：2396235