EXPERIMENT STUDY ON SEDIMENT INCIPIENCE IN BACKWARDFACING STEP FLOW

Flow over a backward-facing step was studied to investigate the effect of large-scale vortex structures on sediment incipience. The transient flow velocity field at the downstream of the backward-facing step was obtained using the technique of Particle Tracking Velocimetry (PTV). The optical amplification technique was employed to measure the instantaneous flow velocities near the bed and the instantaneous bed shear stress was given. The experimental observations revealed a new insight into the oscillation of the large-scale structure and the three-dimensional characteristics of the flow. In particular,very high turbulence intensity,instantaneous horizontal velocity near the bed and the bed shear stress near the reattachment point were observed. The sediment incipient probability obtained from the sequent images of sediment particles near the bed indicates that the critical instantaneous shear stress of the sediment incipience is independent of flow conditions.     

EFFECTS OF SUBMERGED MACROPHYTES ON SEDIMENT SUSPENSION AND NH4-N RELEASE UNDER HYDRODYNAMIC CONDITIONS

Aquatic vegetation affects sediment suspension and nutrient release by changing the flow structure. Experiments on the influence of submerged vegetation on flow structure, sediment suspension, and NH₄-N release were carried in a flume with natural submerged vegetation. Turbulence characteristics in the vegetation section were measured using a three-dimensional acoustic Doppler velocimeter. The effects of submerged vegetation on bed shear stress (τ_b), sediment suspension, and NH₄-N release were analyzed. Results show that with vegetation, bed shear stress is reduced by about 20% – 80%, which, in turn, reduces sediment suspension. The impact of submerged vegetation on sediment suspension and NH₄-N release should be considered along with flow intensity. When the flow Reynolds number is relatively small, the submerged vegetation is quite capable of inhibiting sediment suspension and reducing NH₄-N release, but when the Reynolds number reaches a certain value, the presence of aquatic plants exacerbates sediment suspension and promotes NH₄-N release. Results also reveal that a highly significant positive correlation exists between NH₄-N concentration and water turbidity in both vegetated and non-vegetated channels.     

INCIPIENT MOTION OF NON-COHESIVE SEDIMENT UNDER ICE COVER - AN EXPERIMENTAL STUDY

Based on a series of experiments under both ice-covered and free surface conditions, the present article discusses the role of flow velocity and critical shear Reynolds number for incipient motion of bed material. The influence of the resistance coefficients of both the underside of the ice cover and the channel bed on the location of the maximum velocity has been discussed. In addition, the impacts of ice and composite resistance coefficients on flow velocity for incipient motion of bed material have been assessed. The diagram describing the critical shear Reynolds number and the dimensionless shear stress for the incipient motion of sediment under ice covered conditions with different under cover resistance coefficient has been established. The effects of grain size on densimetric Froude number for incipient motion of bed material have been investigated. A relationship between the densimetric Froude number for incipient motion of bed material and the median grain size of bed material as well as the roughness coefficient of channel bed and roughness coefficient of ice cover has been established.     

HYDRODYNAMIC FORCE ON SMOOTH HORIZONTAL CYLINDER IN UNIFORM OSCILLATORY FLOW

ＨＹＤＲＯＤＹＮＡＭＩＣ　ＦＯＲＣＥ　ＯＮ　ＳＭＯＯＴＨ　ＨＯＲＩＺＯＮＴＡＬ　ＣＹＬＩＮＤＥＲ　ＩＮ　ＵＮＩＦＯＲＭ　ＯＳＣＩＬＬＡＴＯＲＹ　ＦＬＯＷＨＹＤＲＯＤＹＮＡＭＩＣＦＯＲＣＥＯＮＳＭＯＯＴＨＨＯＲＩＺＯＮＴＡＬＣＹＬＩＮＤＥＲＩＮＵＮＩＦ...     

EXPERIMENTAL STUDY ON ABSORPTION OF OIL BY SEDIMENT IN WATER

The absorption behaviour of emulsified oil by sediment (include loess) is studied by experiment. The absorption equation and the relations of absorption capacity with sediment concentration, grain size, salt concentration and temperature are analyzed. The absorbing reaction kinetics process is also studied. The absorption of emulsified oil by sediment in rivers is agreed with the Langmuir-Freundlich absorption equation. Experimental data shows that the larger the equilibrium oil concentration and the salt concentration , the more the absorption capacity. The absorption capacity increases immensely with grain size and temperature reduction.     

MODEL STUDY ON PREVENTING SEDIMENT DEPOSSITION IN WATER INTAKE SYSTEM

The hydraulic and sediment deposition problems in the water intake system of a pumping house were studied by physical model.The experimental results of different working cases indicate that the sediment depositions at the gates,stilling basin and culverts are very few when the system was normally operated,but in the forebay of pumping house,especially in the pumping house for living water,the amount of sediment deposition sometimes is considerably large.At the front of the entry of pumping house forliving water,installing a set of oblique pipes can prevent the coarse grains to enter it,the deposition amount will obviously decrease.     

EXPERIMENTAL STUDY ON BED-LOAD SEDIMENT TRANSPORT IN IRREGULAR WAVE-CURRENT COEXISTENT FIELD

1.　INTRODUCTIONTheproblemofsedimenttransportnearcoastalregionisofgreatimportanceforthesiltationinnavigationalfairways,harbordocksandthechangesinbeachprofileandcoastalmorphology.Underpracticalconditions,dynamicenvironmentisverycomplexbecausethewaveandcurrentarerandomand,theirpropagatingdirectionsarealsouncertain.Sothestudyofsedimenttransportinanirregularwave-currentcoexistentfieldismoreimportantthanthatinpurewaveorpurecurrentfield.Inrecentyears,manyempiricalformulaswereproposedtoexpressth…     

EXPERIMENTAL STUDY ON INSTANTANEOUS DISCHARGE OF UNSORTED PARTICLE CLOUD IN CROSS-FLOW

A series of extensive laboratory experiments were conducted to investigate the transport and mixing of instantaneous discharge of unsorted particle cloud in cross-flow. The following experimental results were obtained： （1） the vertical frontal position and the longitudinal width of the particle cloud in the cross-flow is much larger than those in stagnant water, （2） the smaller cross-flow velocity will normally cause the larger non-dimensional frontal position for the same particle size range and initial volume, （3） the non-dimensional longitudinal width of the particle cloud in the cross-flow increases with the increase of cross-flow velocity. The empirical constants （α1, α3 and α2） and their variance range, which can be used to determine the relationships of non-dimensional vertical frontal position and time, longitudinal width and time, and vertical frontal position and longitudinal width were also obtained through the analysis of experimental data.     

EXPERIMENTAL RESEARCH ON CHARACTERISTICS OF HYDRODYNAMIC PRESSURE SPREADING IN THE BASE GAP OF ARCH INVERTED PLUNGE POOL

1 .　INTRODUCTIONForanytypeofplungepoolinhydraulicengi neering ,thehydrodynamic pressurespreadinginthebasegapwhichlocatesbetweenthetieapronandtherockiscloselyrelatedtothestabilizationoftheapron .Pressurecharacteristicsinthebasegapoftheflat bottom plungepoolwereresearchedbymanyauthors ,e .g .,Virgilio[1] atanearlystageandLiu[2 ] ,Zhang[3] andSun[4 ] inrecent years.However ,thebehaviorofthehydrodynamicpres sureinthebase gapofthearchinverted plungepoolisstillunclear .Thesetwotypesareentirel…     

EXPERIMENTAL STUDY ON BED FORMS AND FLOW RESISTANCE OF LIGHT－WEIGHT MATERIALS WITH DIFFERENT DENSITIES

ＥＸＰＥＲＩＭＥＮＴＡＬＳＴＵＤＹＯＮＢＥＤＦＯＲＭＳＡＮＤＦＬＯＷＲＥＳＩＳＴＡＮＣＥＯＦＬＩＧＨＴ－ＷＥＩＧＨＴＭＡＴＥＲＩＡＬＳＷＩＴＨＤＩＦＦＥＲＥＮＴＤＥＮＳＩＴＩＥＳ￥ＤｕａｎＧｕｏ－ｈｏｎｇ；ＷａｎｇＧｕｉ－ｘｉａｎ（Ｄｅｐｔ．ｏｆＨｙ...     

NUMERICAL AND EXPERIMENTAL STUDY ON LIQUID-SOLID FLOW IN A HYDROCYCLONE

Hydrocyclones are widely used in industry, of which the geometrical design using CFD techniques is gaining more popularity in recent years. In this study, the Euler-Euler approach and the Reynolds stress model are applied to simulate the liquid-solid flowfield in a hydrocyclone. The methodology is validated by a good agreement between experimental data and numerical results. Within the research range, the simulation indicates that the liquid-solid separation mainly occurs in the conical segment, and increasing conical height or decreasing cylindrical height helps to improve the grade efficiencies of solid particles. Based on these results, two of the same hydrocyclones are designed and installed in series to establish a liquid-solid separation system. Many experiments are then conducted under different conditions, in which the effects of the water cut and the second hydrocyclone on the separation are investigated. The results also confirm that smaller solid particles are more susceptible to the inlet conditions, and the second hydrocyclone plays a more important role as the water cut reduces.     

EXPERIMENTAL INVESTIGATION ON THE DRAG REDUCTION CHARACTERISTICS OF TRAVELING WAVY WALL AT HIGH REYNOLDS NUMBER IN WIND TUNNEL

Drag reduction experiments of the traveling wavy wall at high Reynolds number, ranging from 1.46×10⁶ to 5.83×10⁶ based on the free-stream velocity and the model length, were conducted. A suit of traveling wavy wall device was developed and its characteristics of drag reduction at high Reynolds number were investigated. The drag forces of the traveling wavy wall with various wave speeds (c) were measured at different wind speeds (U) in the FL-8 low-speed wind tunnel and compared with the drag force of the flat plate. The results show that the mean drag force of the traveling wavy wall decreases as the value of c/U increases, at different wind velocities, the values of c/U corresponding to minimal drag force of the traveling wavy wall are different, when the values of c/U are larger than 0.6, the mean drag forces of the traveling wavy wall are smaller than those of the flat plate, and the drag reduction can be up to 60%. The drag reduction effectiveness of traveling wavy wall is thus achieved. Furthermore, as the value of c/U increases, the traveling wavy wall can restrain the separation and improve the quality of flow field.     

EXPERIMENTAL STUDY ON GAS-LIQUID TWO-PHASE FLOWS IN AN AREATION TANK BY USING IMAGE TREATMENT METHOD

Particle Image Velocimetry （PIV） technique was employed to study experimentally gas-liquid two-phase flow in an aeration tank. In terms of the PIV principles, an algorithm of PIV based on the Fast Fourier Transformation （FFT） was worked out. The PIV program was developed and verified, and then was used to measure three kinds of states in the testing device. The program was also used to calculate and analyze the related parameters. The experimental data indicate that the bubbles in testing device have the longest resident time and stronger turbulent intensity for the gas-liquid two-phase flow in a special case （Case 3）, resulting in great increase of the oxygen transferring speed and efficiency, whereby providing the basis for the selection design of aeration tank.     

SHIP‐LOCK–INDUCED SURGES IN AN IMPOUNDED RIVER AND THEIR IMPACT ON SUBDAILY FLOW VELOCITY VARIATION

The majority of large rivers are fragmented by dams, and navigation is often supported by the installation of ship locks. Despite their ubiquitous existence, the effect of ship locks on river basin hydrodynamics is rarely considered in an environmental context. Ship‐lock operation induces single‐wave crests or troughs called surges, which propagate along the basin and are subject to reflection at the up‐ and downstream impoundments. We used pressure sensors and acoustic Doppler current profiler measurements to investigate the effects of up‐ and downstream ship locking on the water level and the current velocity dynamics in a 12.9‐km‐long basin of the impounded river Saar (Germany). Ship lifting at the lower dam and the associated water export from the basin results in a negative surge propagating upstream, whereas a descending ship‐lock operation at the upper dam of the basin creates a positive surge propagating downstream. Both types of waves are subject to positive reflection at the opposing dams. Frequent lock operations lead to a complex pattern of multiple superimposing surges. The resulting water level fluctuations are comparable in magnitude with those associated with discharge variations due to hydropower peaking but occur at much shorter timescales. Associated with the water surface displacement during wave passage is a corresponding increase or decrease of the longitudinal current velocity. The magnitude of wave‐induced velocity fluctuations can exceed mean flow velocities by a factor of three and, depending on wave type and direction, can result in a reversal of the main flow direction of the river. Because of their longevity of several hours and superposition effects, ship‐lock–induced surges govern 66.3% and 45.4% of the subdaily variations in flow velocity and water level, respectively. This article concludes with a discussion of the potential effects of lock‐induced flow dynamics in impoundments on oxygen dynamics and methane ebullition. Copyright © 2013 John Wiley & Sons, Ltd.