Effect of accelerating and decelerating flows on incipient motion in sand bed streams

被引:31
作者
Emadzadeh, Adel [1 ,2 ]
Chiew, Yee Meng [2 ]
Afzalimehr, Hossein [1 ]
机构
[1] Isfahan Univ Technol, Water Engn Dept, Esfahan, Iran
[2] Nanyang Technol Univ, Sch Civil & Environm Engn, Singapore, Singapore
关键词
Accelerating flow; Decelerating flow; Incipient motion; Shields parameter; Sand bed; Reynolds stress; VELOCITY DISTRIBUTION; SEDIMENT MOTION; SHEAR VELOCITY; TURBULENCE; STRESS;
D O I
10.1016/j.advwatres.2010.06.014
中图分类号
TV21 [水资源调查与水利规划];
学科分类号
081501 ;
摘要
The effect of flow acceleration and deceleration on velocity, von Karman constant, Reynolds and normal stress distributions under incipient motion were experimentally investigated in this study using eight positive and negative bed slopes ( +/- 0.7%, +/- 0.9%, +/- 1.25% and +/- 1.5%) and three uniform sediments with median grain sizes d(50)=1.8, 1.3 and 0.8 mm. By using an Acoustic Doppler Velocimeter (ADV), the instantaneous velocities were measured at three cross sections 5, 7 and 9-m from the flume entrance giving a total of 72 measured profiles. The results showed that: (1) the shear and normal Reynolds stresses in decelerating flow are greater than those in accelerating flow; (2) the normal Reynolds stress is considerably higher than shear stress in all measured profiles; (3) the von Karman constant associated with non-uniform flows has an average of kappa = 0.26, which is lower than the classical value of 0.4; (4) the critical shear stress and Shields parameter for incipient motion in accelerating flow are considerably higher than that in decelerating flow; and (5) acceleration and deceleration along with slope variation are key factors governing incipient motion in non-uniform flows. (C) 2010 Elsevier Ltd. All rights reserved.
引用
收藏
页码:1094 / 1104
页数:11
相关论文
共 34 条
[1]   Accelerating shear velocity in gravel-bed channels [J].
Afzalimehr, H ;
Anctil, F .
HYDROLOGICAL SCIENCES JOURNAL-JOURNAL DES SCIENCES HYDROLOGIQUES, 2000, 45 (01) :113-124
[2]   Velocity distribution and shear velocity behaviour of decelerating flows over a gravel bed [J].
Afzalimehr, H ;
Anctil, F .
CANADIAN JOURNAL OF CIVIL ENGINEERING, 1999, 26 (04) :468-475
[3]   Determination of bed shear stress in gravel-bed rivers using boundary-layer parameters [J].
Afzalimehr, Hossein ;
Rennie, Colin D. .
HYDROLOGICAL SCIENCES JOURNAL-JOURNAL DES SCIENCES HYDROLOGIQUES, 2009, 54 (01) :147-159
[4]   Influence of decelerating flow on incipient motion of a gravel-bed stream [J].
Afzalimhr, Hossein ;
Dey, Subhasish ;
Rasoulianfar, Pooneh .
SADHANA-ACADEMY PROCEEDINGS IN ENGINEERING SCIENCES, 2007, 32 (05) :545-559
[5]  
[Anonymous], 2008, J GEOPHYS RES EARTH
[6]   Fluid and sediment dynamics of upper stage plane beds [J].
Bennett, SJ ;
Bridge, JS ;
Best, JL .
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, 1998, 103 (C1) :1239-1274
[7]   MEAN FLOW AND TURBULENCE STRUCTURE OVER FIXED, 2-DIMENSIONAL DUNES - IMPLICATIONS FOR SEDIMENT TRANSPORT AND BEDFORM STABILITY [J].
BENNETT, SJ ;
BEST, JL .
SEDIMENTOLOGY, 1995, 42 (03) :491-513
[8]   A systematic analysis of eight decades of incipient motion studies, with special reference to gravel-bedded rivers [J].
Buffington, JM ;
Montgomery, DR .
WATER RESOURCES RESEARCH, 1997, 33 (08) :1993-2029
[9]   Response of velocity and turbulence to sudden change of bed roughness in open-channel flow [J].
Chen, XW ;
Chiew, YM .
JOURNAL OF HYDRAULIC ENGINEERING-ASCE, 2003, 129 (01) :35-43
[10]   INCIPIENT SEDIMENT MOTION ON NON-HORIZONTAL SLOPES [J].
CHIEW, YM ;
PARKER, G .
JOURNAL OF HYDRAULIC RESEARCH, 1994, 32 (05) :649-660