A Computational Fluid Dynamics Investigation of using Large-Scale Geometric Roughness Elements in Open Channels
TL;DR: In this paper, a series of tests of T-shape roughness elements, fixed height, arranged in three different configurations, differ in the number of lines of roughness element.
Abstract: The hydraulic behavior of the flow can be changed by using large-scale geometric roughness elements in open channels. This change can help in controlling erosions and sedimentations along the mainstream of the channel. Roughness elements can be large stone or concrete blocks placed at the channel's bed to impose more resistance in the bed. The geometry of the roughness elements, numbers used, and configuration are parameters that can affect the flow's hydraulic characteristics. In this paper, velocity distribution along the flume was theoretically investigated using a series of tests of T-shape roughness elements, fixed height, arranged in three different configurations, differ in the number of lines of roughness element. These elements were used to find the best configuration of roughness elements that can be applied to change the flow's hydraulic characteristics. ANSYS Parametric Design Language, APDL, and Computational Fluid Dynamics, CFD, was used to simulate the flow in an open channel with roughness elements. CFD can be used to study the hydrodynamics of open channels under different conditions with inclusive details rather than relying on the costly field and time-consuming. Runs were implemented with different conditions, the discharge, and water depth in upstream and downstream of the flume. T-shape roughness elements with height equal to 3cm placed in three different configurations, two lines, four lines, and fully rough configurations were tested. The results show that the effect of roughness elements increasing with increasing the number of lines of roughness elements. Cases of four lines and fully rough configurations have almost the same hydraulic performance by having the same results of the velocity decrease percentage, which is decreased by approximately about 66% and 61% of the control case's velocity in the zone near the roughness elements consequently. But the difference is that four lines configuration is affected in a part of the test section. This behavior increases the velocity values by about 11% in the other side and by about 10% near the free surface in the case of four lines configuration and increased by about 32% above the roughness elements in a fully rough configuration.
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TL;DR: In this article , the authors investigated the hydrodynamics performance of the spillway and the stilling basin of AlAdhiam Dam by using numerical simulation models under gated situations.
Abstract: The AlAdhaim Dam is located 133 kilometers northeast of Baghdad. It is a multipurpose dam and joints the Iraqi dam system in 2000. It has a storage capacity of 1.5 billion m3. The dam has an ogee spillway with a length of 562 m, a crest level of 131.5 m.a.m.s.l. and a maximum discharge capacity of 1150 m3/s at its maximum storage height of 143 m.a.m.s.l. This research aimed to investigate the hydrodynamics performance of the spillway and the stilling basin of AlAdhiam Dam by using numerical simulation models under gated situations. It was suggested to modify the dam capacity by increasing the dam's storage capacity by installing gates on the crest of the dam spillway. The FLUENT program was used to simulate the flow over the spillway. The free surface was calculated using the volume of fluid (VOF) method. To deal with turbulence, the SST k-ω turbulence model was used. The study showed that the spillway is capable of carrying the designed flood discharge and the modified conditions with negative pressure behind the gate and at some points along the spillway. Hydraulic jumps occur at various distances throughout the plunge pool depending on the incoming velocity in the flip bucket.
TL;DR: In this paper , the authors examined the vibrations produced by hydropower operations to improve embankment dam safety and suggested an enhanced turbine operating system, reducing stress on the dam body and increasing dam operation life.
Abstract: This study examines the vibrations produced by hydropower operations to improve embankment dam safety. This study consists of two parts: In the first part, ANSYS-CFX was used to generate a three-dimensional (3-D) finite volume (FV) model to simulate a vertical Francis turbine unit in the Mosul hydropower plant. The pressure pattern result of the turbine model was transformed into the dam body to show how the turbine unit's operation affects the dam's stability. The upstream reservoir conditions, various flow rates, and fully open inlet gates were considered. In the second part of this study, a 3-D FE Mosul dam model was simulated using an ANSYS program. The operational turbine model's water pressure pattern is conveyed to the dam's turbine-shared zone. The maximal and minimal upstream reservoir water levels were investigated. A control program was created depending on the principle stress model results collected from the operation of the hydropower plant with the minimum principal stress on the dam body. This research suggests an enhanced turbine operating system, reducing stress on the dam body and increasing dam operation life.
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Book•
01 Jun 1995
TL;DR: This chapter discusses the development of the Finite Volume Method for Diffusion Problems, a method for solving pressure-Velocity Coupling in Steady Flows problems, and its applications.
Abstract: *Introduction. *Conservation Laws of Fluid Motion and Boundary Conditions. *Turbulence and its Modelling. *The Finite Volume Method for Diffusion Problems. *The Finite Volume Method for Convection-Diffusion Problems. *Solution Algorithms for Pressure-Velocity Coupling in Steady Flows. *Solution of Discretised Equations. *The Finite Volume Method for Unsteady Flows. *Implementation of Boundary Conditions. *Advanced topics and applications. Appendices. References. Index.
7,412 citations
TL;DR: In this article, the authors used a three-dimensional computational fluid dynamics solver to investigate flow characteristics for variations of discharge, channel slope and boulder size, spacing, and pattern, and derived relationships for estimating water depth and velocity in a rock-ramp fish pass as a function of discharge and structure geometry.
Abstract: The flow characteristics in a rock-ramp fish pass can be significantly altered by the boulder arrangement This study used a three-dimensional computational fluid dynamics solver to investigate flow characteristics for variations of discharge, channel slope and boulder size, spacing, and pattern This study derived relationships for estimating water depth and velocity in a rock-ramp fish pass as a function of discharge and structure geometry The flow resistance varies significantly with emergent boulder spacing and is nearly constant for submerged boulders This study derives relationships for the drag coefficient and submergence ratio to forecast average flow velocity using a flow-resistance equation Based on maximum velocity and a slow velocity zone, this study recommends effective boulder spacing in the longitudinal and transverse directions for two different boulder patterns Finally, this study developed a design procedure for designing a rock-ramp fish pass
31 citations
TL;DR: In this article, the hydraulic characteristics of unsteady flow in Al-Gharraf River in order to define the locations that facing problems and suggesting the necessary treatments are described.
Abstract: One and two-dimensional hydraulic models simulations are important to specify the hydraulic characteristics of unsteady flow in Al-Gharraf River in order to define the locations that facing problems and suggesting the necessary treatments. The reach in the present study is 58200m long and lies between Kut and Hai Cities. Both numerical models were simulated using HEC-RAS software, 5.0.4, with flow rates ranging from 100 to 350 m3/s. Multi-scenarios of gates openings of Hai Regulator were applied. While the openings of Al-Gharraf Head Regulator were ranged between 60cm to fully opened. The suitable manning roughness for the unsteady state was 0.025. The obtained results show that the average velocities for the one-dimensional model were ranged between 0.36 and 0.5 m/s, and the average water surface elevations range between 15.14 m and 17.84 m. While these values ranged between 0.25 and 0.44 m/s and 14.125 and 18.82 m respectively for the two-dimensional model. The simulation results of the two-dimensional model were more accurate than their corresponding one-dimensional model, due to more agreement of these values with measured values, which achieved minimum values of the root mean square error and the determination coefficient.
10 citations
TL;DR: In this paper, the effects of surface roughness on a turbulent boundary layer in a relatively high Reynolds flow was examined using FLUENT, a commercial Computational Fluid Dynamics software.
Abstract: Flow development in an open-channel with rough beds was investigated using FLUENT, a commercial Computational Fluid Dynamics (CFD) software. The Renormalization Group (RNG) k-ɛ turbulence model was used for subcritical flow cases. The Volume of Fluid (VOF) method was used to allow the free-surface to deform freely with the underlying turbulence. The main purpose of this study was to examine the effects of the different types of surface roughness on a turbulent boundary layer in a relatively high Reynolds flow. The determination of velocity profile in turbulent open channels with rough bed is a difficult task due to the significant effects of the roughness. The velocity distributions in the log-region for the rough wall were determined. The roughness function ΔU
+, the characteristic downward shift of the logarithmic part of the mean velocity profile, was found to be more than 12 for three rough surfaces the roughness function, ΔU
+ scales logarithmically with normalized effective height y+.
9 citations
"A Computational Fluid Dynamics Inve..." refers background in this paper
...(Abbaspour and Kia, 2014), studied the effect of strip semi-cylindrical roughness established in two different configurations on a turbulent layer in a relatively high Reynolds number....
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TL;DR: In this article, the flow characteristics of Tigris River within Baghdad City was studied, the reach involved was about 49km in which it represents the urban zone beginning from the north of the Baghdad City at Al-Muthana Bridge to the confluence of the Tigris river with the Diyala River south of Baghdad, using steady flow one-dimensional hydraulic model to achieve raising of water levels within this reach during drought periods.
Abstract: The main source of water supply in Iraq is the surface water, especially Tigris and Euphrates Rivers and their tributaries. In the recent years there was a great drop in the water levels of Tigris River within Baghdad City which had affected the operation of twelve water supply projects located on the banks of Tigris River in Baghdad City, due to significant climate changes, and the expansion of hydraulic construction (dams) and implementation of new irrigation projects in Turkey, these factors have greatly reduced the water flowrates of river by about 46%. In the present study the flow characteristics of Tigris River within Baghdad City was studied, the reach involved was about 49km in which it represents the urban zone beginning from the north of the Baghdad City at Al-Muthana Bridge to the confluence of Tigris River with the Diyala River south of Baghdad, using steady flow one-dimensional hydraulic model to achieve raising of water levels within this reach during drought periods. This model was implemented using HEC-RAS software.Three sets of observation data were used to calibrate the model to estimate suitable Manning roughness coefficient (n) considering the root mean square error (RSME) as an accurate indicator. The results showed that n of value 0.032 for the main river bed and 0.040 for flood banks of the river gave the best results with minimum RMSE of 0.076. Several treatments were suggested such as construction of barrage, inflatable weir, and the use of obstruction for the purpose of raising water levels. Moreover, selection of the suitable site of these treatments or hydraulic structures was studied, as well as their cost was analyzed. The results show that the proper solution for maintain the required water levels that ensure continuous operation of water supply project was the construction of an inflatable weirs, due to low initial cost, simplicity of operation, their ability to inflate and deflate quickly and easily to prevent upstream flooding, and offering a high level of control and easy method for recapturing water.
6 citations