山区河道粗颗粒床面垂线流速分布规律试验研究
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摘要
粗颗粒床面普遍存在于山区河道中,在浅水条件下,水深与床面颗粒粒径的比值h/d较小,此时河道中水流垂线流速分布难以用传统的对数公式或对数补偿公式进行准确描述。在室内概化水槽中,利用玻璃珠及乒乓球模拟粗颗粒床沙,对不同h/d下的垂线流速分布规律进行了系统的试验研究。前人研究发现,不同淹没度(h/d)下的理论床面取值并不统一。考虑到工程应用方便,作者采用普通粗糙床面河道下的理论床面值,即y0为0.2d。将试验测得数据进行无量纲化处理后与对数补偿公式计算得到的理论值对比,并率定公式中的系数B与尾流系数Π到最佳。结果表明:当h/d较小时,系数B随着h/d的增大减小,尾流系数Π随着h/d的增大而增大;而当h/d较大时,B与Π都趋于一个常数。最后,建立了适用于山区粗颗粒卵砾石泥沙河道的垂线流速分布公式,并将其与众多前人试验数据进行拟合检验。检验结果表明,作者提出的垂线流速分布公式具有较高的计算精度,同时对于普通粗糙床面河道,该公式也具有很好的适应性。
In mountain rivers with coarse sediments, the ratio of water depth to sediment diameter(h/d) is relatively small especially under the condition of shallow water depth. Therefore, the vertical velocity distribution along the river cannot be described accurately with traditional logarithmic or logarithmic-wake law. In this paper, flume experiments were carried out with two kinds of sediments(glass beads d=1.4 cm and pinpong d=4 cm) to test the influence of coarse sediment on vertical velocity distribution under different h/d. In the presence of coarse sediment bed,one of the problems encountered is how to determine the reference level y0. For practical purpose, the present study assumes that y0 does not varies with h/d, namely, y0=0.2 d. The measured data were first converted to dimensionless and then compared to theoretical results calculated by logarithmic-wake law. In addition, the coefficient B and another wake coefficient Π in in logarithmic compensation formula were calibrated to fit for the measured data. The results indicate that when the value of h/d is small, the coefficient B decreases with the increase of h/d while the wake coefficient Π presents an opposite trend; when the value of h/d becomes larger, both B and Π tend to a constant. Finally, a modified logarithmicwake law is derived to describe the velocity distribution in mountain river flows with small h/d. The modified model agrees well with the experimental data conducted in the present laboratory flume. Furthermore, it also has a good adaptability to riverbed with coarse sediments.
In mountain rivers with coarse sediments, the ratio of water depth to sediment diameter(h/d) is relatively small especially under the condition of shallow water depth. Therefore, the vertical velocity distribution along the river cannot be described accurately with traditional logarithmic or logarithmic-wake law. In this paper, flume experiments were carried out with two kinds of sediments(glass beads d=1.4 cm and pinpong d=4 cm) to test the influence of coarse sediment on vertical velocity distribution under different h/d. In the presence of coarse sediment bed,one of the problems encountered is how to determine the reference level y0. For practical purpose, the present study assumes that y0 does not varies with h/d, namely, y0=0.2 d. The measured data were first converted to dimensionless and then compared to theoretical results calculated by logarithmic-wake law. In addition, the coefficient B and another wake coefficient Π in in logarithmic compensation formula were calibrated to fit for the measured data. The results indicate that when the value of h/d is small, the coefficient B decreases with the increase of h/d while the wake coefficient Π presents an opposite trend; when the value of h/d becomes larger, both B and Π tend to a constant. Finally, a modified logarithmicwake law is derived to describe the velocity distribution in mountain river flows with small h/d. The modified model agrees well with the experimental data conducted in the present laboratory flume. Furthermore, it also has a good adaptability to riverbed with coarse sediments.
引文
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[2]Nezu I,Nakagawa H.Turbulence in open-channel flows[M].Rotterdam:Monographseries of IAHR,1993,45:56-58
[3]胡春宏,惠遇甲.明渠挟沙水流运动的力学与统计规律[M].北京:科学出版社,1995.
[4]Liang Yue,Cao Shuyou,Yang Fengguang,et al.Study on generalized velocity distribution formula of flows in smooth wide open channe[J].Journal of Hydroelectric Engineering,2013,32(5):147-152.[梁越,曹叔尤,杨奉广,等.光滑宽浅明渠流动垂线流速分布公式研究[J].水力发电学报,2013,32(5):147-152.]
[5]Cui H,Singh V P.One dimensional velocity distribution in open channels using Tsallis entropy[J].Journal of Hydrologic Engineering,ASCE,2014,19(2):290-298.
[6]Kumbhakar M,Ghoshal K.One-dimensional velocity distribution in open channels using Renyi entropy[J].Stochastic Environmental Research and Risk Assessment,2017,31(4):949-959.
[7]Keulegan G H.Laws of turbulent flow in open channels[J].Journal of Research of the National Bureau of Standards,1938,21(6):707-741.
[8]Yalin S M.Mechanics of sediment transport[M].New York:Pergamon Press,1972.
[9]Nezu I,Rodi W.Closure to“open-channel flow measurements with a laser doppler anemometer”by Iehisa Nezu and Wolfgang Rodf[J].Journal of Hydraulic Engineering,1987(12):1574-1576.
[10]Wu Min.Study on velocity distribution and resistance characteristic in mountain river[D].Chengdu:Sichuan University,2016.[毋敏.山区卵石河道流速及阻力特性研究[D].成都:四川大学,2016.]
[11]Kumbhakar M,Ghoshal K.One-dimensional velocity distribution in open channels using Renyi entropy[J].Physica AStatistical Mechanics&Its Applications,2016,450:546-559.
[12]Dong Zengnan,Wang Jinjun,Chen Changzhi,et al.Hydraulic characteristics of uniform turbulent flow in open channel with rough bed[J].Science China,1992(5):541-547.[董曾南,王晋军,陈长植,等.粗糙床面明渠均匀紊流水力特性[J].中国科学,1992(5):541-547.]
[13]Yang Bin,Yang Shengfa.The experimental study on the velocity distribution over the high gradient gravel bed[J].Chinese Journal of Hydrodynamics,2005,20(2):207-213.[杨斌,杨胜发.大比降卵石河床水流运动试验研究[J].水动力学研究与进展,2005,20(2):207-213.]
[14]Nikora V,Goring D,McEwan I,et al.Spatially averaged open-channel flow over rough bed[J].Journal of Hydraulic Engineering,ASCE,2001,127(2):123-133.
[15]钱宁,万兆惠.泥沙运动力学[M].北京:科学出版社,1983.
[16]Garcia M H.Sedimentation engineering,processes,measurements,modeling,and practice[M].Reston:ASCE Press,2008.
[17]Tu H.Velocity distribution in unsteady flow over gravelbeds[D].Lausanne Switzerland:école Polytechnique Féderale de Lausanne,1991.
[18]Song T.Velocity and turbulence distribution in non-uniform and unsteady open-channel flow[D].Lausanne:école Polytechnique Féderale de Lausanne,1994.
[19]Einstein H A,El-Samni E S A.Hydrodynamic forces on a rough wall[J].Review of Modern Physics,1949,21(3):520-524.
[20]Lassabatere L,Pu J H,Bonakdari H,et al.Velocity distribution in open channel flows:Analytical approach for the outer region[J].Journal of Hydraulic Engineering,ASCE,2013,139(1):37-43.
[21]Kironoto B A.Turbulence characteristics of uniform and non-uniform,rough open-channel flow[D].Lausanne:école Polytechnique Féderale de Lausanne,1993.