Water

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10 pages, 3506 KiB

Open AccessArticle

An Experimental Study of Roughness Elements to Design Fixed-Bed Hydraulic Model—A Step-by-Step Process and an Application in Vietnam

by Chau Kim Tran, Hoang Cong Vo, Hien Phu La, Binh Thi Hoa Le, Nguyen Dong Dang, Trung Nguyen Le, Vu Tran and Thuat Duc Hoang

Water 2023, 15(1), 72; https://doi.org/10.3390/w15010072 - 25 Dec 2022

Viewed by 2076

Abstract

The calibration of the water level in a hydraulic model experiment is a time-consuming task. In this study, the authors proposed a guide to adjust the water level in the fixed-bed hydraulic experiment, by establishing a connection between the water level increase (ΔZ) [...] Read more.

The calibration of the water level in a hydraulic model experiment is a time-consuming task. In this study, the authors proposed a guide to adjust the water level in the fixed-bed hydraulic experiment, by establishing a connection between the water level increase (ΔZ) in the model with other factors such as roughness diameter (d), roughness density (s), and flow velocity (v). Based on the results of 105 model experiments with different d, s, and v, the study also suggested a process to design a model experiment. The results of the study were used to build a fixed-bed hydraulic experiment for a river section passing through the Ialy hydropower plant in Vietnam. The results showed that after 01 time of implementation, the water level in the experiment was close to the observed water level. The differences between the calculated and measured water levels have been significantly reduced, from 0.027–0.036 m to 0.003–0.008 m. This finding shows that the approach of the study saves time and effort in the process of setting up a hydraulic experiment. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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24 pages, 6555 KiB

Open AccessArticle

Effects of Nonlinearity on Velocity, Acceleration and Pressure Gradient in Free-Stream Zone of Solitary Wave over Horizontal Bed—An Experimental Study

by Chang Lin, Ming-Jer Kao, James Yang, Juan-Ming Yuan and Shih-Chun Hsieh

Water 2022, 14(22), 3609; https://doi.org/10.3390/w14223609 - 9 Nov 2022

Cited by 1 | Viewed by 2072

Abstract

For solitary waves on a horizontal bed, the study deals experimentally with the high ratio of wave height (H₀) to still water depth (h₀) that amplifies the wave nonlinearity. The value of H₀/h₀ tested [...] Read more.

For solitary waves on a horizontal bed, the study deals experimentally with the high ratio of wave height (H₀) to still water depth (h₀) that amplifies the wave nonlinearity. The value of H₀/h₀ tested in a wave flume ranges from 0.050 to 0.550, indicating the shift from a quasi-linear solitary wave to a highly nonlinear one. A high-speed particle image velocimetry (HSPIV) and a flow visualization technique of particle-trajectory tracking method are utilized to measure velocity fields and identify near-bed flow structures. The unsteady free-stream velocities with equal magnitude take place in a free-stream zone, FSZ). The FSZ underlies the internal flow zone, over which the external free surface of solitary wave exists and is situated beyond the boundary layer. The spatio-temporal variation of free-stream velocity, moving in phase with the free surface elevation, characterizes the pattern of pressure gradient in the FSZ and thus dominates the behavior of boundary layer flow. Accordingly, nonlinear effects on the time series as well as the maximum values of horizontal velocity, particle acceleration, and pressure gradient in the FSZs of solitary waves are presented. Before, at, and after the wave crest’s intersection with a given measurement location, favorable, zero, and adverse pressure gradients occur in the FSZ, respectively. For H₀/h₀ = 0.179, 0.363, and 0.550, the values of the dimensionless maximum free-stream velocity are about 3.10, 5.32, and 6.20 times that (= 0.0473) for H₀/h₀ = 0.050; and the corresponding values of the dimensionless maximum adverse pressure gradient are about 5.74, 14.54 and 19.84 times that (= 0.0061) for H₀/h₀ = 0.050. This evidence highlights the nonlinear effect on the kinematic and hydrodynamic features of solitary waves. Finally, the effect of nonlinearity on the relationship between the dimensionless time for the maximum adverse pressure gradient in the FSZ and that for the incipient flow reversal in the bottom boundary layer is explored for the first time. It is found that the incipient flow reversal takes place immediately after the maximum adverse pressure gradient, together with a decrease in the dimensionless time for flow reversal if H₀/h₀ increases. The fact accentuates the nonlinear effect on the incipient flow reversal right above the bed. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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18 pages, 14729 KiB

Open AccessArticle

Two-Phase Flow Modeling for Bed Erosion by a Plane Jet Impingement

by Damien Pham Van Bang, Miguel Uh Zapata, Georges Gauthier, Philippe Gondret, Wei Zhang and Kim Dan Nguyen

Water 2022, 14(20), 3290; https://doi.org/10.3390/w14203290 - 18 Oct 2022

Cited by 2 | Viewed by 2311

Abstract

This paper presents experimental and numerical studies on the erosion of a horizontal granular bed by a two-dimensional plane vertical impinging jet to predict the eroded craters’ size scaling (depth and width). The simulations help understand the microscopic processes that govern erosion in [...] Read more.

This paper presents experimental and numerical studies on the erosion of a horizontal granular bed by a two-dimensional plane vertical impinging jet to predict the eroded craters’ size scaling (depth and width). The simulations help understand the microscopic processes that govern erosion in this complex flow. A modified jet-bed distance, accounting for the plane jet virtual origin, is successfully used to obtain a unique relationship between the crater size and a local Shields parameter. This work develops a two-phase flow numerical model to reproduce the experimental results. The numerical techniques are based on a finite volume formulation to approximate spatial derivatives, a projection technique to calculate the pressure and velocity for each phase, and a staggered grid to avoid spurious oscillations. Different options for the sediment’s solid-to-liquid transition during erosion are proposed, tested, and discussed. One model is based on unified equations of continuum mechanics, others on modified closure equations for viscosity or momentum transfer. A good agreement between the numerical solutions and the experimental measurements is obtained. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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17 pages, 9284 KiB

Open AccessArticle

Velocity Measurements in Highly Aerated Flow on a Stepped Chute without Sidewall Constraint Using a BIV Technique

by Martí Sánchez-Juny, Soledad Estrella, Jorge Matos, Ernest Bladé, Eduardo Martínez-Gomariz and Enrique Bonet Gil

Water 2022, 14(16), 2587; https://doi.org/10.3390/w14162587 - 22 Aug 2022

Cited by 2 | Viewed by 2348

Abstract

The lack of sidewalls in a spillway leads to lateral expansion of the flow and, consequently, a non-uniform transversal flow rate distribution along the chute. The present work shows the velocity field measured in a physical model of a 1 V:0.8 H steeply [...] Read more.

The lack of sidewalls in a spillway leads to lateral expansion of the flow and, consequently, a non-uniform transversal flow rate distribution along the chute. The present work shows the velocity field measured in a physical model of a 1 V:0.8 H steeply sloping stepped spillway without sidewalls. An application of a Bubble Image Velocimetry (BIV) technique in the self-aerated region is shown, using air bubbles entrained into the flow downstream of the inception point as tracers. The results indicate that, for small dimensionless discharges and sufficiently downstream of the point of inception, the free-surface velocity compares relatively well with the corresponding air–water interfacial velocity previously obtained with a double-tip fiber optical probe in the same facility. In turn, the velocity profiles along the normal to the pseudo-bottom, far downstream of the inception point, are reasonably in agreement with the air–water interfacial velocity profiles in the inner part of the skimming flow, with the largest differences being verified in the upper skimming flow region near the free-surface. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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18 pages, 20414 KiB

Open AccessArticle

Relative Energy Variation Characteristics Considering Interaction between Waves and Vegetation Structure

by Ruey-Syan Shih, Chi-Yu Li, Wen-Kai Weng and Chih-Hung Lin

Water 2022, 14(16), 2567; https://doi.org/10.3390/w14162567 - 20 Aug 2022

Viewed by 2040

Abstract

Although viscous sediment environments along the coast strongly attenuate waves, the attenuation dynamics and physical mechanism governing the attenuation process remain relatively unknown. Extremely complex interactions between muddy seabed have become increasingly important for wave evolution studies pertaining to coastal areas. The coastal [...] Read more.

Although viscous sediment environments along the coast strongly attenuate waves, the attenuation dynamics and physical mechanism governing the attenuation process remain relatively unknown. Extremely complex interactions between muddy seabed have become increasingly important for wave evolution studies pertaining to coastal areas. The coastal protection function of mangroves was confirmed during the 2004 South Asian tsunami. Nevertheless, most research has been limited to macro-qualitative analyses, including those on variations in the transmission coefficient K_t and reflection coefficient K_r, and subsequent comparisons. However, determining the micro-physical characteristics is challenging, similar to coastal vegetation analyses with respect to mangrove vegetation characteristics. This study aims to quantify the attenuation difference in the wave energy owing to the coastal vegetation structure, under different layout conditions and combinations. Particle image velocimetry (PIV) technology is used to explore the variations in the velocity field and velocity distribution during the interaction process and calculate the wave-induced kinetic energy before and after setting up the vegetation structure. The research results emphasize that the resistance and frictional effects generated by vegetation are inversely proportional to the size of the stem, and the variation of kinetic energy determined from the velocity distribution and the thickness of the vegetation stem is mainly due to the larger frictional resistance of dense vegetation, relative to the fast flow velocity above the vegetation. Different vegetation heights slightly affect the short-period waves; however, the impact on energy reduction was smaller. For long-period waves, vegetation height significantly reduces wave kinetic energy. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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21 pages, 13484 KiB

Open AccessArticle

Laboratory Study on Flow Characteristics during Solitary Waves Interacting with a Suspended Horizontal Plate

by Xuyang Niu, Yuxiang Ma and Guohai Dong

Water 2022, 14(15), 2386; https://doi.org/10.3390/w14152386 - 1 Aug 2022

Cited by 4 | Viewed by 2179

Abstract

A series of laboratory experiments were conducted to investigate the 2–D kinematic field evolution around a suspended plate induced by solitary waves. The plate–type structure was rigid and suspended above the mean water level, while the solitary waves were generated by the wave [...] Read more.

A series of laboratory experiments were conducted to investigate the 2–D kinematic field evolution around a suspended plate induced by solitary waves. The plate–type structure was rigid and suspended above the mean water level, while the solitary waves were generated by the wave maker to simulate the nearshore tsunami waves. The ratio of incident wave height to water depth was in the range of [0.200, 0.333], and the structural suspended height was in the range of [0.067, 0.200]. The velocity field around the deck was measured using the non–intrusive image–based PIV (Particle Image Velocimetry) method. As a result, the flow evolution was categorized into three phases: green water tongue generated, green water overtopping, and flow separation. Flow evolutions in different conditions presented obvious similarities in general but several differences in detail. The measured maximum horizontal and vertical velocities were around 1.9 C₀ and 0.8 C₀, respectively, where C₀ is the maximum flow speed of the incident wave. Ritter’s analytical solution for the dam–break flow problem was examined and compared with the measured data. The accuracy of this solution for the present subject is significant in the period of T ∈ (0.6, 0.9). The adequate experimental data are valuable as a benchmark problem for further numerical model refinement and the improvement of fluid theory. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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19 pages, 3104 KiB

Open AccessArticle

The Effect of Rough Rigid Apron on Scour Downstream of Sluice Gates

by Mohammad Aamir, Zulfequar Ahmad, Manish Pandey, Mohammad Amir Khan, Ali Aldrees and Abdullah Mohamed

Water 2022, 14(14), 2223; https://doi.org/10.3390/w14142223 - 14 Jul 2022

Cited by 13 | Viewed by 3901

Abstract

Presented in this paper is an experimental study on scour downstream of rough and smooth stiff aprons under the influence of wall jets. The effect of various parameters on asymptotic scour depth is studied. The analysis of data reveals that maximum scour depth [...] Read more.

Presented in this paper is an experimental study on scour downstream of rough and smooth stiff aprons under the influence of wall jets. The effect of various parameters on asymptotic scour depth is studied. The analysis of data reveals that maximum scour depth reduces with increasing sediment size, sluice opening, and apron length. It is directly proportional to densimetric Froude number. Maximum equilibrium scour depth initially decreases with increasing tailwater level (up to a minimum), but thereafter an increase is observed. The effect of roughness of stiff apron on scour is studied and quantification of decline in maximum scour depth due to roughness is carried out. Scour profiles and their temporal variation are also studied. A regression-based equation to predict equilibrium scour depth under smooth and rough apron is proposed, which conforms to experimental data. Based on the conclusions of this study, it is recommended to use roughness over the surface of stiff apron to confine scour under-wall jets. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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21 pages, 8808 KiB

Open AccessArticle

Role of Grain Size Distribution and Pier Aspect Ratio in Scouring and Sorting around Bridge Piers

by Takeyoshi Chibana, Rose Quiocho and Kenji Watanabe

Water 2022, 14(13), 2066; https://doi.org/10.3390/w14132066 - 28 Jun 2022

Cited by 2 | Viewed by 2107

Abstract

Several bridge piers were visited, and their scour hole was characterized into three zones: scour, transition, and mound zones. The observed onsite sorting and scouring patterns were recreated through flume experiments with varying pier aspect ratio (1:1, 1:2, 1:4 and 1:6) and sediment [...] Read more.

Several bridge piers were visited, and their scour hole was characterized into three zones: scour, transition, and mound zones. The observed onsite sorting and scouring patterns were recreated through flume experiments with varying pier aspect ratio (1:1, 1:2, 1:4 and 1:6) and sediment geometric standard deviation (σ_g). The experiments showed that maximum scour depth decreased with non-uniformity; 52.7 mm, 20.2 mm, and 16.6 mm are the respective maximum scour depth of beds with σ_g = 1.4, 2.5, and 5.2. While aspect ratio has minimal effect on maximum scour depth values, it has noticeable effects on scour shape and asymmetry. The location of the lowest point of the scour shifted further downstream as σ_g increased. The number of occurrences where the location of the lowest point is outside the upstream cylindrical hemisphere is zero (0) for σ_g = 1.4, three (3) for σ_g = 2.5, and five (5) for σ_g = 5.2. The observed processes of upstream-to-downstream propagation of scour may explain the gradual decrease in fines on the surface, as well as the asymmetry of the scour, confirming the role of combined effects of grading of the bed material and piers’ aspect ratio in the scour-forming process. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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21 pages, 20867 KiB

Open AccessArticle

Numerical Study of Mixing Process by Point Source Pollution with Different Release Positions in a Sinuous Open Channel

by Hai Zhu, Shengjie Lu, Lingling Wang, Jieru Xu and Saiyu Yuan

Water 2022, 14(12), 1903; https://doi.org/10.3390/w14121903 - 13 Jun 2022

Cited by 1 | Viewed by 2155

Abstract

The process of pollutant mixing is significantly influenced by secondary flow and turbulence in meandering rivers. To investigate the influence of different point source release positions on the pollutant mixing process in sinuous open channel flows, a 3D large-eddy simulation (LES) model based [...] Read more.

The process of pollutant mixing is significantly influenced by secondary flow and turbulence in meandering rivers. To investigate the influence of different point source release positions on the pollutant mixing process in sinuous open channel flows, a 3D large-eddy simulation (LES) model based on OpenFOAM was established to simulate the process of passive scalar transport in a sinuous channel with a rectangular cross-section. After verification by a flume experiment, two sets of cases in which the point sources were arranged at identical intervals in spanwise and streamwise directions were configured to evaluate the mixing efficiency. The effect of flow structure, secondary motion, and the turbulent viscosity on the scalar transport and mixing was discussed. The distribution of scalar as well as the scalar flux was analyzed in detail, and the fluctuation characteristics were also described. The results demonstrate that due to the existence of secondary flow in the sinuous channel, different transverse and streamwise release positions of the point source have significant influence on mixing efficiency and spatial distribution of the pollutant. The point source placed near the center of the cross-section in transverse or near the apex of the bend in streamwise result in higher mixing efficiency. Mixing efficiency calculated by different indices can be different, which requires comprehensive assessment. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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22 pages, 10930 KiB

Open AccessArticle

Application of Image Technique to Obtain Surface Velocity and Bed Elevation in Open-Channel Flow

by Yen-Cheng Lin, Hao-Che Ho, Tzu-An Lee and Hsin-Yu Chen

Water 2022, 14(12), 1895; https://doi.org/10.3390/w14121895 - 13 Jun 2022

Cited by 5 | Viewed by 3298

Abstract

The frequency of droughts and floods is increasing due to the extreme climate. Therefore, water resource planning, allocation, and disaster prevention have become increasingly important. One of the most important kinds of hydrological data in water resources planning and management is discharge. The [...] Read more.

The frequency of droughts and floods is increasing due to the extreme climate. Therefore, water resource planning, allocation, and disaster prevention have become increasingly important. One of the most important kinds of hydrological data in water resources planning and management is discharge. The general way to measure the water depth and discharge is to use the Acoustic Doppler Current Profiler (ADCP), a semi-intrusive instrument. This method would involve many human resources and pose severe hazards by floods and extreme events. In recent years, it has become mainstream to measure hydrological data with nonintrusive methods such as the Large-Scale Particle Image Velocimetry (LSPIV), which is used to measure the surface velocity of rivers and estimate the discharge. However, the unknown water depth is an obstacle for this technique. In this study, a method combined with LSPIV to estimate the bathymetry was proposed. The experiments combining the LSPIV technique and the continuity equation to obtain the bed elevation were conducted in a 27 m long and 1 m wide flume. The flow conditions in the experiments were ensured to be within uniform and subcritical flow, and thermoplastic rubber particles were used as the tracking particles for the velocity measurement. The two-dimensional bathymetry was estimated from the depth-averaged velocity and the continuity equation with the leapfrog scheme in a predefined grid under the constraints of Courant–Friedrichs–Lewy (CFL). The LSPIV results were verified using Acoustic Doppler Velocimetry (ADV) measurements, and the bed elevation data of this study were verified using conventional point gauge measurements. The results indicate that the proposed method effectively estimated the variation of the bed elevation, especially in the shallow water level, with an average accuracy of 90.8%. The experimental results also showed that it is feasible to combine the nonintrusive imaging technique with the numerical calculation in solving the water depth and bed elevation. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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16 pages, 5448 KiB

Open AccessFeature PaperArticle

A PIV-Based Algorithm for Simultaneous Determination of Multiple Velocity Fields from Stratified Crossflows in Single Field of View

by Wei-Liang Chuang and Sheng-Mei Lin

Water 2022, 14(12), 1877; https://doi.org/10.3390/w14121877 - 10 Jun 2022

Viewed by 2273

Abstract

This study presents a new imaging-based algorithm for simultaneously determining multiple velocity fields from stratified crossflows optically captured in a single field of view. The concept implements an additional automatic peak finding scheme into the conventional particle image velocimetry (PIV) analysis procedure, identifying [...] Read more.

This study presents a new imaging-based algorithm for simultaneously determining multiple velocity fields from stratified crossflows optically captured in a single field of view. The concept implements an additional automatic peak finding scheme into the conventional particle image velocimetry (PIV) analysis procedure, identifying multiple prominent peak cross-correlation coefficients corresponding to the flows in various directions. To examine the validity, synthetic particle images generated by computer visions and image data acquired by PIV measurements are employed in the validation study. With both root-mean-square errors (RMSEs) in magnitude and direction being found to be temporally random, the validation results suggest that the performance of the new algorithm is ideal for steady or quasi-steady flows. This implies that the new algorithm may also work well for the flows repeatable with identical initial and boundary conditions. For transient flows, more valuable data can be obtained with the new algorithm, particularly in large-scale experiments or field measurements. Moreover, tests on synthetic images show that the RMSE in magnitude decays exponentially with increasing tracking particle density, and a density of 30% is found to be the lowest for the minimum RMSE in magnitude. Discussions on the error reduction, limitations of the new algorithm, suggestions for applications, and guidance on spurious vector removal are given as well. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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18 pages, 2807 KiB

Open AccessFeature PaperArticle

Parametric Study on Abutment Scour under Unsteady Flow

by Rajkumar V. Raikar, Jian-Hao Hong, Anandrao R. Deshmukh and Wen-Dar Guo

Water 2022, 14(11), 1820; https://doi.org/10.3390/w14111820 - 6 Jun 2022

Cited by 5 | Viewed by 2429

Abstract

Experimental results on scour at abutments under unsteady clear water flow condition are presented. Three shapes of short abutments (abutment length/upstream flow depth < 1) were tested, namely, rectangular/vertical wall, semi-circular, and trapezoidal/45° wing-wall abutments embedded in uniform sands of two sizes having [...] Read more.

Experimental results on scour at abutments under unsteady clear water flow condition are presented. Three shapes of short abutments (abutment length/upstream flow depth < 1) were tested, namely, rectangular/vertical wall, semi-circular, and trapezoidal/45° wing-wall abutments embedded in uniform sands of two sizes having d₅₀ = 0.52 mm and 0.712 mm. The unsteadiness of the flow is considered in the form flood hydrographs of three forms, namely: advanced flood hydrograph (Type I), symmetrical flood hydrograph (Type II), and delayed flood hydrograph (Type III) with the flow maintained at clear water condition in all cases. The experimental findings are used to represent the influence of various parameters on scour depth at bridge abutments. It was observed that the scour depth at rectangular abutments is greater than that at trapezoidal and semi-circular abutments. The scour depths at abutments embedded in finer sediments are greater than those in coarser sediments. In addition, based on the study of effect of three flood hydrographs, it was noticed that the delayed flood hydrograph yields greater scour depth as compared to the other two cases. Further, based on the method of superposition and the correction of shape factor, a semi-empirical model using dimensionless parameters is proposed to compute the temporal evolution of scour depth at abutments under unsteady clear water conditions. The parameters used in this model include flow shallowness, flow intensity, sediment coarseness, and time factor. It was found that the proposed model corresponds well with the data of time-dependent scour depth in uniform sediments obtained from the present experiments (unsteady flows) and reported by different investigators (steady flows). Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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12 pages, 9590 KiB

Open AccessFeature PaperArticle

A Combined O/U-Tube Oscillatory Water Tunnel for Fluid Flow and Sediment Transport Studies: The Hydrodynamics and Genetic Algorithm

by Cheng-Hsien Lee, Jia-You Chen, Fang-Shou Lee and Li-Chiu Chang

Water 2022, 14(11), 1767; https://doi.org/10.3390/w14111767 - 31 May 2022

Viewed by 2099

Abstract

This study proposes an oscillatory water tunnel (O/U-tube) equipped with two impellers to drive flows. The O/U-tube consists of two modes: U-tube mode and O-tube mode. The former can generate oscillatory flow, while the latter can produce both oscillatory and unidirectional flows with [...] Read more.

This study proposes an oscillatory water tunnel (O/U-tube) equipped with two impellers to drive flows. The O/U-tube consists of two modes: U-tube mode and O-tube mode. The former can generate oscillatory flow, while the latter can produce both oscillatory and unidirectional flows with velocities up to 1.6 m/s. The hydrodynamics of the U-tube and O-tube modes were examined analytically. For the U-tube mode, a sine-varying rotational speed for the impeller caused higher harmonic components for the velocity, owing to the local inertia and gravity forces. In the steady state of the O-tube mode, owing to the resistance force, the flow velocity was proportional to the rotational speed. To generate the target flow conditions, two open-loop control schemes were proposed according to the analytic approach for the U-tube mode and a genetic algorithm for the O-tube mode. The analytic approach was based on a hydrodynamic model with a given flow condition. In the genetic algorithm, the rotational speed was represented by a square root of the Fourier series. The optimal coefficients of the Fourier series to generate the target flow were determined by using the genetic algorithm and the hydrodynamic model. Both approaches were experimentally validated. Consequently, the O/U-tube with the open-loop schemes can be used to generate the desired oscillatory and unidirectional flows. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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13 pages, 1892 KiB

Open AccessArticle

Investigation on the Cavity Backwater of Chute Aerators under Various Atmospheric Pressures

by Yameng Wang, Jun Deng and Wangru Wei

Water 2022, 14(9), 1513; https://doi.org/10.3390/w14091513 - 9 May 2022

Cited by 2 | Viewed by 1777

Abstract

A chute aerator is a device that entrains air into water and protects against cavitation erosion. The state of the jet cavity determines the aerator efficiency under different flow conditions. In the case of a low Froude number and low velocity, backwater is [...] Read more.

A chute aerator is a device that entrains air into water and protects against cavitation erosion. The state of the jet cavity determines the aerator efficiency under different flow conditions. In the case of a low Froude number and low velocity, backwater is generated in the jet cavity. In severe cases, this backwater blocks the air intake holes and affects air intake efficiency. With the development and construction of water conservancy projects, an increasing number of dams have been constructed at altitudes above 3000 m. The influence of cavity backwater depth at reduced atmospheric pressures is unknown and may increase the risk of high-speed aerated flows in high-altitude areas. In this study, the relevant parameters of backwater were measured at various atmospheric pressures, including the jet length, cavity subpressure, backwater depth, and net cavity length. The pressure difference of atmospheric pressure can range from 0 to 94 kPa. The test results indicate that a decrease in atmospheric pressure causes variations in the cavity subpressure. The absolute value of the difference between the inside and outside of the cavity decreases with a decrease in atmospheric pressure. An empirical formula for calculating the subpressure at different atmospheric pressures is proposed for P_N < 0.1. The air velocity in the ventilation shaft decreases with a decrease in atmospheric pressure. The effects of variation in the atmospheric pressure on jet length can be ignored because the variation in jet length with different atmospheric pressures was constant. Additionally, the influence of varying atmospheric pressure on the cavity backwater is evident. The backwater depth decreases with a decrease in atmospheric pressure. When the atmospheric pressure decreases from 96 to 6 kPa, the maximum reduction in backwater depth is over 50%. Atmospheric pressure is a parameter that affects cavity backwater. Based on the measured backwater depth data, an empirical formula for calculating the backwater depth at different atmospheric pressures is proposed. This indicates a relationship between the atmospheric pressure and backwater depth under different flow conditions. It was further found that the bottom cavity may require a larger air intake volume at low atmospheric pressures and that it is necessary to optimize the aerator and the ventilation system. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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16 pages, 5191 KiB

Open AccessArticle

Breaking Solitary Wave Impact on a Vertical Seawall

by Yun-Ta Wu

Water 2022, 14(4), 583; https://doi.org/10.3390/w14040583 - 15 Feb 2022

Cited by 3 | Viewed by 3445

Abstract

Wave interactions with vertical and sloping seawalls are indeed complicated, especially for the impacts due to breaking waves, which are unsteady, turbulent and multi-phase. Available studies successfully measured the impact pressure due to waves acting on seawalls, whereas the associated flow velocity and [...] Read more.

Wave interactions with vertical and sloping seawalls are indeed complicated, especially for the impacts due to breaking waves, which are unsteady, turbulent and multi-phase. Available studies successfully measured the impact pressure due to waves acting on seawalls, whereas the associated flow velocity and turbulence characteristic received limited attention, indicating that the momentum of such violent free-surface flows cannot be determined. In this study, new experiments were carried out in a laboratory-scale wave flume using a non-intrusive image-based measuring technique (bubble image velocimetry, BIV) to measure the flow velocities due to a shoaling solitary wave impinging on and overtopping a vertical seawall. By varying the wave height of solitary waves, the breaking point of a shoaling wave can be changed. As such, the impact point of a breaking wave in relation to the seawall can be thereby adjusted. Considering the same still-water depth, two wave height conditions are studied so as to produce different levels of aerated flows. Effects of high- and low-aerated cases on free surface elevations, flow velocities and turbulence characteristics are presented so as to develop a better understanding of wave-structure interactions. More specifically, the maximum velocities and turbulence intensities at different evolutionary phases are identified for these two cases. Full article

(This article belongs to the Special Issue Advances in Experimental Hydraulics, Coast and Ocean Hydrodynamics)

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