scholarly journals Macro-turbulent characteristcs of pressures in hydraulic jump formed downstream of a stepped spillway

RBRH ◽  
2017 ◽  
Vol 22 (0) ◽  
Author(s):  
Carolina Kuhn Novakoski ◽  
◽  
Eliane Conterato ◽  
Marcelo Marques ◽  
Eder Daniel Teixeira ◽  
...  
Keyword(s):  
Pressure Fluctuation ◽  
Hydraulic Jump ◽  
Pressure Fluctuations ◽  
Longitudinal Distribution ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Stilling Basin ◽  
Large Pressure ◽  
Skewness Coefficient ◽  
Mean Pressure

ABSTRACT Stilling basins are structures built at the base of the spillway to dissipate energy, by means of a hydraulic jump. Hydraulic jump is a turbulent phenomenon that causes large pressure fluctuation in the stilling basin bottom, and can damage the sink structure through mechanisms such as fatigue, upflit pressure and cavitation. The use of stepped spillways allows the dissipation of a parcel of the energy while the water falls by the spillway, allowing a reduction in the stilling basin’s dimensions and cost. The present article presents the analysis of the longitudinal distribution of mean pressure, pressure fluctuations, skewness coefficient and kurtosis coefficient, derived from tests on physical hydraulic models. Pressure values measured in a stilling basin downstream of a stepped spillway (for Froude numbers between 5 and 8) were compared with data observed in a stilling basin downstream of a smooth spillway with a radius of concordance between the chute and the basin (for Froude numbers between 4.5 and 10). The results of these studies show that the mean pressures and the pressure fluctuation observed in the stilling basin downstream of stepped spillway present maximum values at the spillway’s closest point, differing, thus, from those at the smooth spillway. The longitudinal distribution of skewness and kurtosis coefficients enabled to define the positions for flow detachment start, roller ending and as well as the ending of the influence of the hydraulic jump over the flow.

scholarly journals Longitudinal distribution of extreme pressures in a hydraulic jump downstream of a stepped spillway

RBRH ◽  
2017 ◽  
Vol 22 (0) ◽  
Author(s):  
Carolina Kuhn Novakoski ◽  
Roberta Ferrão Hampe ◽  
Eliane Conterato ◽  
Marcelo Giulian Marques ◽  
Eder Daniel Teixeira
Keyword(s):  
High Pressure ◽  
Hydraulic Jump ◽  
Pressure Fluctuations ◽  
Longitudinal Distribution ◽  
Stepped Spillway ◽  
Pressure Data ◽  
Stilling Basin ◽  
Considerable Portion ◽  
Dissipation Structure ◽  
The Impact

ABSTRACT The overflow system of a dam safely controls the water level of a reservoir. The design of these structures should predict the damage caused by the action of the turbulent flow to which they are subject to. The combination formed by a stepped spillway followed by a stilling basin promotes a considerable portion of the energy dissipation in the actual chute of the stepped spillway but it is not sufficient to completely avoid the risk of damaging the basin. In this paper, we analyze the longitudinal distribution of extreme pressures in a stilling basin downstream of a stepped spillway. The study was based on the instant pressure data from the tests carried out in a physical model in the Laboratório de Obras Hidráulicas in IPH/UFRGS. Thus, it was found that the pressure behavior is similar to that observed in studies involving smooth chute spillways, except in the area surrounding the base of the stepped spillway, where high pressure fluctuations may occur. This happens as a result of the impact caused by the flow in the dissipation structure, which is not observed downstream of smooth chute spillways due to the existence of a vertical concordance curve between the spillway and the stilling basin.

Prediction of pressure fluctuations on sloping stilling basins

2006 ◽  
Vol 33 (11) ◽  
pp. 1379-1388 ◽  
Author(s):  
A Güven ◽  
M Günal ◽  
A Çevik
Keyword(s):  
Neural Network ◽  
Pressure Fluctuation ◽  
Hydraulic Jump ◽  
Regression Models ◽  
Pressure Fluctuations ◽  
Network Models ◽  
Neural Network Models ◽  
Mean Pressure ◽  
Stilling Basins ◽  
The Mean

Various types of hydraulic jump occurring on horizontal and sloping channels have been analyzed experimentally, theoretically, and numerically and the results are available in the literature. In this study, artificial neural network models were developed to simulate the mean pressure fluctuations beneath a hydraulic jump occurring on sloping stilling basins. Multilayers feed a forward neural network with a back-propagation learning algorithm to model the pressure fluctuations beneath such a type of hydraulic jump (B-jump). An explicit formula that predicts the mean pressure fluctuation in terms of the characteristics that contribute most to the hydraulic jump occurring on the sloping basins is presented. The proposed neural network models are compared with linear and nonlinear regression models that were developed using considered physical parameters. The results of the neural network modelling are found to be superior to the regression models and are in good agreement with the experimental results due to relatively small values of error (mean absolute percentage error).Key words: neural networks, pressure fluctuation, hydraulic jump, sloping stilling basin, explicit NN formulation, regression analysis.

scholarly journals Uniform flow and energy dissipation of hydraulic-jump-stepped spillways

2020 ◽  
Vol 20 (4) ◽  
pp. 1546-1553
Author(s):  
Yu Zhou ◽  
Jianhua Wu ◽  
Fei Ma ◽  
Jianyong Hu
Keyword(s):  
Energy Dissipation ◽  
Water Flow ◽  
Hydraulic Jump ◽  
Flow Region ◽  
Uniform Flow ◽  
Stepped Spillway ◽  
Flow Depth ◽  
Clear Water ◽  
Air Concentration ◽  
Stepped Spillways

Abstract In skimming flow, a uniform flow can be achieved and the flow depth, velocity and air concentration remain constant if a stepped spillway is sufficiently long. In this study, physical model experiments were performed to investigate the uniform characteristics and energy dissipation of a hydraulic-jump-stepped spillway, which is a new type of stepped spillway for increasing the unit discharge capacity and energy dissipation. Based on the redefinition of uniform flow, experimental results show that at a given stepped spillway slope, a smaller height for the beginning of the uniform flow region, a greater uniform aerated flow depth and a greater uniform equivalent clear water flow depth can be obtained as compared with the traditional stepped spillway due to strong aeration in the aeration basin. Under the condition of uniform flow, the energy dissipation rate of stepped spillways can be estimated by the equivalent clear water flow depth with given inflow conditions. Compared with the traditional stepped spillway, the uniform flow over the hydraulic-jump-stepped spillway has a smaller specific energy, revealing that the hydraulic-jump-stepped spillway is more advantageous for dissipating energy, especially at large unit discharges.

scholarly journals Predicting the Flow Velocity at the Toe of a Labyrinth Stepped Spillway

2021 ◽  
Vol 18 (1) ◽  
pp. 20-25
Author(s):  
Jaafar S. Maatooq
Keyword(s):  
Kinetic Energy ◽  
Flow Velocity ◽  
Smooth Surface ◽  
Air Entrainment ◽  
Physical Models ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Stilling Basin ◽  
Major Variable ◽  
Jet Velocities

The velocity at the toe of a spillway is a major variable when designing a stilling basin. Reducing this velocity leads to reduce the size of the basin as well as the required appurtenances which needs for dissipating the surplus kinetic energy of the flow. If the spillway chute is able to dissipate more kinetic energy, then the resulting flow velocity at the toe of spillway will be reduced. Typically, stepped spillway is able to dissipate more kinetic energy than that of a smooth surface. In the present study, the typical uniform shape of the steps has been modified to a labyrinth shape. It is postulated that a labyrinth shape can increase the dissipation of kinetic energy through increasing the overlap between the forests of nappe will circulating the flow that in turns leading to further turbulence. This action can reduce the jet velocities near the surfaces, thus minimizing cavitation. At the same time the increasing of circulation regions will maximize the opportunity for air entrainment which also helps to dissipate more kinetic energy. The undertaken physical models were consisted of three labyrinth stepped spillways with magnification ratios (width of labyrinth to width of conventional step) WL/W are 1.1, 1.2, and 1.3 as well as testing a conventional stepped spillway (WL/W=1). It is concluded that the spillway chute coefficient is directly proportional to the labyrinth ratio and its value decreases as this ratio increases.

scholarly journals Analysis of the longitudinal distribution of pressures near the ends of the vertical and horizontal faces in stepped spillway of slope 1V: 0.75H

RBRH ◽  
2018 ◽  
Vol 23 (0) ◽  
Author(s):  
Fabrício Machado Osmar ◽  
Alba Valéria Brandão Canellas ◽  
Priscila dos Santos Priebe ◽  
Lorena Silva Saraiva ◽  
Eder Daniel Teixeira ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Physical Model ◽  
Longitudinal Distribution ◽  
Stepped Spillway ◽  
Dimensionless Numbers ◽  
Stepped Spillways ◽  
Pressure Coefficients ◽  
General Finding ◽  
Pressure Fields ◽  
Negative Pressures

ABSTRACT Stepped spillways have been widely used for flood runoff due to of their constructive advantages and in regards to energy dissipation during the drop, allowing downstream dissipation structures to be designed in smaller dimensions. Due to the need for further studies on the effect of runoff in the chute of the stepped spillway and the analysis of dimensionless numbers used to characterize the longitudinal distribution of the pressures acting on the faces of the steps of a spillway, this study aims to characterize the acting forces on the steps of said spillways. Analyses were performed on a physical model of spillway with a slope of 1V: 0.75H and steps with a height of 6 centimeters. The pressure fields on the steps were analyzed and compared with results found in literature. As a general finding concerning the pressure in the horizontal faces, it was ascertained that the traction and the compression loads have relatively similar magnitudes, the negative pressures being more intense. Regarding the maximum pressures at the horizontal faces of the steps, it should be emphasized that the maximum values of compression have occurred at the end of the chute and that the lower discharges yielded higher values of pressure coefficients.

scholarly journals A Novel Comparative Statistical and Experimental Modeling of Pressure Field in Free Jumps along the Apron of USBR Type I and II Dissipation Basins

Mathematics ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 2155
Author(s):  
Seyed Nasrollah Mousavi ◽  
Daniele Bocchiola
Keyword(s):  
Pressure Field ◽  
Pressure Fluctuations ◽  
Maximum Pressure ◽  
Slab Thickness ◽  
Type I ◽  
Bureau Of Reclamation ◽  
Pressure Transducers ◽  
Large Pressure ◽  
The Us ◽  
Mean Pressure

Dissipation basins are usually constructed downstream of spillways to dissipate energy, causing large pressure fluctuations underneath hydraulic jumps. Little systematic experimental investigation seems available for the pressure parameters on the bed of the US Department of the Interior, Bureau of Reclamation (USBR) Type II dissipation basins in the literature. We present the results of laboratory-scale experiments, focusing on the statistical modeling of the pressure field at the centerline of the apron along the USBR Type I and II basins. The accuracy of the pressure transducers was ±0.5%. The presence of accessories within basinII reduced the maximum pressure fluctuations by about 45% compared to basinI. Accordingly, in some points, the bottom of basinII did not collide directly with the jet due to the hydraulic jump. As a result, the values of pressure and pressure fluctuations decreased mainly therein. New original best-fit relationships were proposed for the mean pressure, the statistical coefficient of the probability distribution, and the standard deviation of pressure fluctuations to estimate the pressures with different probabilities of occurrence in basinI and basinII. The results could be useful for a more accurate, safe design of the slab thickness, and reduce the operation and maintenance costs of dissipation basins.

ESTIMATION OF HYDRAULIC JUMP CHARACTERISTICS IN STILLING BASIN WITH GUIDE WALLS

2012 ◽  
Vol 40 (6) ◽  
pp. 1599-1609
Author(s):  
Habib A.A. ◽  
Abdel-Azim M. Ali ◽  
Abd-Allh Y.M ◽  
Saleh y.k.
Keyword(s):  
Hydraulic Jump ◽  
Stilling Basin

Experimental Investigation of Pressure Fluctuations on Inner Wall of a Centrifugal Pump

2019 ◽  
Vol 36 (4) ◽  
pp. 401-410 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Bao-Ling Cui ◽  
Zu-Chao Zhu ◽  
Yu-Liang Zhang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
High Flow ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Pressure Distributions ◽  
Blade Passing Frequency

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

Comparison of Mixture and Multifluid Models for In-Nozzle Cavitation Prediction

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Michele Battistoni ◽  
Sibendu Som ◽  
Douglas E. Longman
Keyword(s):  
Mixture Model ◽  
Bubble Dynamics ◽  
National Laboratory ◽  
Pressure Fluctuations ◽  
Argonne National Laboratory ◽  
Numerical Approach ◽  
Fuel Injectors ◽  
Cavitation Inception ◽  
Noncondensable Gases ◽  
Large Pressure

Fuel injectors often feature cavitation because of large pressure gradients, which in some regions lead to extremely low pressures. The main objective of this work is to compare the prediction capabilities of two multiphase flow approaches for modeling cavitation in small nozzles, like those used in high-pressure diesel or gasoline fuel injectors. Numerical results are assessed against quantitative high resolution experimental data collected at Argonne National Laboratory using synchrotron X-ray radiography of a model nozzle. One numerical approach uses a homogeneous mixture model with the volume of fluid (VOF) method, in which phase change is modeled via the homogeneous relaxation model (HRM). The second approach is based on the multifluid nonhomogeneous model and uses the Rayleigh bubble-dynamics model to account for cavitation. Both models include three components, i.e., liquid, vapor, and air, and the flow is compressible. Quantitatively, the amount of void predicted by the multifluid model is in good agreement with measurements, while the mixture model overpredicts the values. Qualitatively, void regions look similar and compare well with the experimental measurements. Grid converged results have been achieved for the prediction of mass flow rate while grid-convergence for void fraction is still an open point. Simulation results indicate that most of the vapor is produced at the nozzle entrance. In addition, downstream along the centerline, void due to expansion of noncondensable gases has been identified. The paper also includes a discussion about the effect of turbulent pressure fluctuations on cavitation inception.

Sign in / Sign up

Export Citation Format

Share Document