共查询到19条相似文献,搜索用时 218 毫秒
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采用3种不同粒径粗糙度的人工加糙明渠和光滑PVC壁面明渠,在9种不同底坡、6组不同的流量条件下,研究了明渠均匀流中糙率值与粗糙度、弗汝德数间相关关系。研究结果表明:(1)相同流量条件下:随着弗汝德数Fr的增大,糙率n值逐渐增大。同一弗汝德数Fr下,粗糙度Δ越大,糙率n值越大。(2)不同绝对粗糙度下:随着弗汝德数Fr增大,糙率n值增大。当Fr0.70时(即缓流),糙率n值与弗汝德数Fr有关,与绝对粗糙度Δ关系不大,即n=f(Fr);当0.7Fr1.0时(即缓流),糙率值n与弗汝德数Fr和绝对粗糙度Δ都有关系,即n=f(Fr,Δ);当Fr1.0时(即急流),糙率n值与绝对粗糙度Δ有关,与Fr关系不大,即n=f(Δ)。 相似文献
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为研究矩形渠道水流的阻力规律,采用了3种不同粗糙度的人工加糙渠道进行试验。研究结果表明在均匀流条件下,对同一粗糙度明渠,水力条件变化时糙率系数不是恒定不变的,它会随着流量的加大而呈对数减小,随着渠道宽深比的增大而呈对数增大,同时随着雷诺数Re和弗汝德数Fr的增加而呈幂函数减小。同时表明,不同的壁面粗糙度对糙率系数影响很大,进而影响水流的水力特性。即流量相同条件下,当壁面粗糙度增大时,断面水深增大,平均流速减小,雷诺数和弗汝德数均减小。并根据试验资料拟合出了糙率系数和等效粗糙度之间的关系式。 相似文献
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为探究不同底坡对渠道糙率的影响,采用9种不同底坡的人工渠道,在6种不同的流量条件下研究糙率随底坡和流量变化的规律。试验结果表明:在明渠均匀流条件下,随着底坡的变化,渠道糙率存在3种不同的变化规律。当Fr<1时,随着流量的增大,糙率逐渐减小;当11.51时,随着流量的增大糙率逐渐增大。当流量相同时,随着底坡的增大,糙率逐渐增大。在缓流渠道中,渠道糙率随底坡变化的速率很快;在急流渠道中,渠道糙率随底坡变化的速率较慢,糙率趋于某一常数。 相似文献
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为了研究明渠水流水力特性变化规律,在室内实验的基础上,采用矩形明渠变坡水槽,通过改变边壁条件、坡度和流量进行实验,得到了较好的实验数据。实验结果表明:边壁条件和坡度相同的情况下,随着流量的增加,水深呈线性增加,平均流速和雷诺数呈现幂函数增大;当Fr1时,弗劳德数随着流量的增加而增加;当1Fr1.526时,弗劳德数随着流量的增加先增加而后减小;当Fr1.526时,弗劳德数随着流量的增加而减小;曼宁糙率系数随着流量的增加呈对数减小趋势。边壁条件和流量相同的情况下,随着坡度的增大,水深呈减小趋势,平均流速、雷诺数、弗劳德数和曼宁糙率系数均呈现增加的趋势。并由实验数据得出了雷诺数与坡度和流量关系的经验公式。 相似文献
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人工明渠糙率值确定及其变化规律研究,是水力学的重要课题之一,当前并无糙率随流量变动趋势关系的定论。以新疆阿勒泰哈巴河县养殖渠人工渠道为例,通过试验对不同底坡条件及相同底坡条件下糙率随流量变化的趋势规律进行研究。结果表明,流态是影响哈巴河县养殖渠人工渠道糙率的主要因素,此外,渠道糙率的取值及变动趋势还与底坡、弗汝德数、水深等因素有关。结果可为糙率特性的研究和水力计算中糙率准确取值的确定提供理论依据。 相似文献
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对于不同粗糙壁面的人工渠道中的均匀流,选取弗劳德数Fr、底坡比降i、雷诺数Re、流量Q、渠道平均水深h为参数,通过水力模型试验,确定这些因素对糙率系数的影响程度,分析各要素间的主次关系及相关关系。结果表明:对糙率影响较大的水力要素排序依次为弗劳德数Fr、渠道平均水深h和底坡比降i,糙率与流量、雷诺数无关。 相似文献
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含淹没植被明渠水位及糙率变化试验研究 总被引:1,自引:0,他引:1
采用概化水槽试验研究了在不同植物间距、水流条件下,含淹没植被明渠水位、曼宁糙率系数的变化特征,给出了含淹没植被明渠的糙率经验公式.试验结果表明:相同的流量、水深条件下,明渠的水位壅高值和水面比降均随植物间距的减小而逐渐增大,当植物枝叶相互间贴近或交叉时,植物对明渠水位、比降的影响程度相对较大;水深基本相同、植物排列方式相同的情况下,随着流量的增加,水面比降基本呈线性增大趋势;水深相同的条件下,含淹没植被明渠糙率受水流流速的影响较小. 相似文献
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This paper relates differences in flow hydraulics between a main channel (MC) and a side channel (SC) of a river to patterns of upstream migration by Neritina virginea (Neritidae: Gastropoda), a dominant diadromous snail in streams of Puerto Rico (Greater Antilles). Near‐bed water velocity, snail density and shell size were measured on a weekly basis between August and December 2000 along cross‐sections in a main channel (MC) and an adjacent channel (SC) under a bridge crossing of the Río Mameyes of Northeastern Puerto Rico. Near‐bed velocity and water depth were used to compute Reynolds (Re) and Froude (Fr) numbers, and to classify flows within each channel. During base flow conditions (<2 m3 s−1), flow was chaotic and supercritical (Fr > 1) in the MC, and non‐chaotic and subcritical (Fr < 1) in the SC. Higher mean densities (>100 ind m−2) of relatively small snails (mean ± s.d., 6.3 ± 2.8 mm) were consistently recorded in the MC. Conversely, the SC had lower mean densities (<20 ind m−2) and significantly larger snails (7.6 ± 2.4 mm). Within the MC, migratory groups preferred near‐bed velocities > 0.8 m s−1. Within the SC, they preferred the channel thalweg and depths > 30 cm. The spatial arrangement that was observed between and within the channels may be related to food resources, predation pressure or biomechanics. Characteristics of preferred upstream migration pathways of N. virginea must be accounted when building road crossings in coastal streams with diadromous fauna. Published in 2007 by John Wiley & Sons, Ltd. 相似文献
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为了研究长距离渠道糙率的合理取值,依据北疆输水工程总干渠2011—2016年逐日水位、流量数据,采用曼宁公式反算典型断面糙率,并构建一维非恒定流水动力模型对渠段糙率进行校核,分析长距离渠道糙率在渠段间的差异及边壁粗糙度随运行时间的变化情况。结果表明:断面的实测糙率与顺直渠段糙率相符,总干渠顺直段糙率在0.015~0.016,弯道明显的渠段,弯度校正因子在1.15~1.50,大小与弯道复杂程度相关;渠道糙率随运行时间呈增长趋势,总干渠等效粗糙度中期运行的年增幅约为18.54%。 相似文献
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为深入探索植被倒伏条件下水流结构的内在规律,开展植被茎秆直径对坡面流水流特性影响的试验研究。试验固定坡度为1. 0%,倒伏角度为20°,取茎秆直径为2 mm、3 mm、4 mm进行室内明渠流模拟试验。结果表明:在相同直径条件下,随水深增大,Darcy-Weisbach阻力系数逐渐增大,雷诺数呈线性增大,弗劳德数呈幂函数形式下降;在相同水深条件下,随茎秆直径增大,DarcyWeisbach阻力系数增大,雷诺数与弗劳德数随之而减小,且当茎秆直径每增加1 mm,阻力系数平均增大33. 76%,雷诺数平均减小2. 57%,弗劳德数平均减小8. 33%。 相似文献
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The paper shows how a change in irrigation canal roughness can influence the flow passing through offtakes. HEC-RAS steady
state model was calibrated with changing Manning's “n” and used for flow simulation in a modern irrigation system in Iran. Results showed that the Manning's “n” obtained from the model calibration procedure (0.025) was different significantly from its primary value (0.015) along the
canal. The increase was due to poor canal maintenance. The changes in roughness of about − 20%, − 40%, 40%, and 100% of the
primary value can significantly influence the upstream water level and the discharge passing through some offtakes. In order
to better evaluation and comparison of offtakes, sensitivity indicator “offtake sensitivity to roughness” was introduced.
An analytical approach helped us to define an equation for direct estimation of the sensitivity indicator under steady state
uniform conditions for trapezoidal canals. Evaluation of water level fluctuations and the sensitivity indicator shows that
only two of the offtakes are sensitive to roughness changes because of being located at the upstream of submerged cross-regulators.
It can be concluded that the effects of roughness changes could be more important for offtakes located far from the downstream
cross-regulators or near the submerged cross-regulators. 相似文献
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自然河道中植被呈现多种多样的分布状态,为探究不同布置形态下刚性淹没植被对水流特性的影响,利用室内水槽模拟含刚性淹没植被的明渠进行试验研究。结果表明:刚性淹没植被的布置形态对明渠流水流特性影响显著。在本文研究的植被布置形态下的水深、植被阻力系数与植被粗糙系数均增大,表现为交错型布置斑块型布置线性布置;流速与雷诺数均减小,表现为线性布置斑块型布置交错型布置;糙率n随着平均流速与水力半径之积VR的增大而减小。 相似文献
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Payam Khosravinia Mohammad Reza Nikpour Amir Malekpour Ali Hosseinzadeh Dalir 《河流研究与利用》2019,35(2):159-168
In an open‐channel confluence, deep scour holes and depositional point bars are usually formed due to high bed‐shear stresses and secondary circulations. In the present study, presuming the effectiveness of channel geometry on the flow dynamics at the confluence, some variables including different side slope angles of the main channel (θ = 45°, 60°, 75°, 90°), lateral to downstream discharge ratio (Qr), and downstream densimetric Froude number (Frg3) were experimentally studied under clear‐water condition for the confluence angle α = 90°. According to the results, the increase of θ led to a greater penetration of scour hole across the main and tributary channels, whereas a little scour development was observed along those channels. Meanwhile, an increase in Qr and Frg3 caused further scouring, but their effects on the dimensions of scour hole diminished with increase of θ. Thus, with increase of Qr from 0.194 to 0.552, the mean penetration rate of scour hole to all directions for θ = 45°, 60°, 75°, and 90° was obtained 42.8%, 32.4%, 25%, and 20.5%, respectively. In addition, considering the effect of θ, Qr, and Frg3, some empirical relationships were obtained for estimating the penetration length of scour hole. The derived relationships show that Frg3 plays more important role on the dimensions of scour hole than θ. 相似文献