Stepped Spillways Research Articles

A New Type of Pre-Aeration Stepped Spillway

Aiming to increase energy dissipation and prevent the cavitation potential of a traditional stepped spillway (TSS) at large unit discharges, a kind of pre-aeration stepped spillway, called a hydraulic-jump-stepped spillway (HJSS), is introduced in this paper. Unlike a TSS, a basin added upstream of the stepped chute in the HJSS plays a vital role in the hydraulic performance owing to the formation of a hydraulic jump in the basin. This paper presents experimental research on the hydraulic performance of the HJSS in comparison to a TSS with the same chute slope (θ = 39.3°) for a wide range of unit discharges, including the flow pattern, energy dissipation, pre-aeration effect, and maximum splash height. The results showed that the HJSS corresponded to a large energy dissipation rate, the air was effectively entrained at the inlet of the stepped chute, and there was an observation of splash formation in the foregoing and downstream steps. Under large unit discharges, the HJSS maintained an energy dissipation rate exceeding 80%. Additionally, at the inlet, the air concentrations reached 4.5% on the bottom and 11.2% on the sidewall. The findings of this research could be used as a general guideline for stepped spillway design with large unit discharges.

Two-Phase Flow Modelling Based on Roughness Surface Effect of Roller Compacted Concrete

One of the most important considerations that are interest to researchers on the stepped spillway in hydraulic structure is the location of the point at which the flow begins to transform into two phase-flow and the development of boundary layers. In this study, an unconventional rough surface was used (RCC materials), which has completely different properties from what is used in previous laboratory studies, which uses smooth surfaces in reality to represent the actual roughness of the surface. Benchmark mixes are evaluated as a reference standard concrete to determine the optimal combination proportions for RCC according to The U.S. Army Corps of Engineers Standard. A laboratory study of different models enhanced by a mathematical model CFD with VOF technics to described the two- phase interaction to investigate the location of the inception point and compare the results with the proposed equations assumed by different researchers in this topic. The results obtained from the study showed a clear effect of surface roughness on the location of the inception point and the formation of the boundary layer for laboratory models. It’s clearly found that the two-phase flow starts with closer locations than it is for conventional models and the ratios vary (10 % - 20 %) according to the discharge values (where the effect of surface roughness is evident in the low discharges compared to the high discharges in which the boundary Lear effect begins to fade.

Energy dissipation performance of labyrinth and harmonic stepped spillways

ABSTRACT Stepped spillways are structures that dissipate the energy on steps, especially in topography, where building the energy dissipate pool is impossible as long as required. For this reason, stepped spillways are one of the critical topics that have attracted the attention of researchers for many years. It has been the subject of many studies, especially because the step geometry is an effective parameter in the energy dissipation rate. In this study, the effect of the labyrinth and harmonic geometry on the plan on energy dissipation performance is examined using the open-source OpenFOAM software. The 11 different geometries were analyzed in detail and discussed with the literature results. For analysis, the k − ω SST turbulence model and the multi-phase solver interFoam were utilized. The results showed that the number of cycles is an effective parameter for energy dissipation performance; the energy dissipation rate increases when effective crest length increases, and labyrinth and harmonic models could dissipate about 20% more energy than the flat model.

Improved Numerical Model to Investigate Self-Aeration along Stepped Spillway

Improved Numerical Model to Investigate Self-Aeration along Stepped Spillway

Characteristics of flow passing over Hydrofoil Crested Stepped Spillway

A spillway comprises several sections, primarily the crest and chute, essential for safe water flow from an upstream reservoir to a downstream river. Incorporating a hydrofoil crest and stepped chute features creates an efficient Hydrofoil-Crested Stepped Spillway (HCSS). The hydraulic features of the 60 HCSS models, which were designed through the National Advisory Committee for Aeronautics (NACA) equation, are assessed through laboratory experiments under a skimming flow regime, where the five hydrofoil formation indexes (t), three numbers of steps (Ns), and four chute angles (θ) are of concern. The findings indicate that an escalation in the ratio of upstream depth (yup) to spillway height (P), correlates with a rise in the discharge coefficient (Cd) in HCSSs. Furthermore, augmenting the t effectively boosts the Cd value. On average, the Cd value of the crest at t = 1 surpasses that at t = 0.2 by 20 %. This increase in t accentuates the curvature of the spillway crest, thereby enhancing the curvature of streamlines and reducing the flow distance therein. The Energy Dissipation Ratio (EDR) of HCSS is influenced by factors such as t (positively correlated), Ns (positively correlated), and θ (negatively correlated). Optimal performance of the HCSS is observed at t = 1, where both the Cd and EDR reach their peak values.

Numerical Analysis of Flow Characteristics and Energy Dissipation on Flat and Pooled Stepped Spillways

Numerical Analysis of Flow Characteristics and Energy Dissipation on Flat and Pooled Stepped Spillways

Investigation of Improved Energy Dissipation in Stepped Spillways Applying Bubble Image Velocimetry

This study investigates skimming flow regimes, two-phase air–water flow conditions, and simple measures to improve energy dissipation in stepped spillways. Experiments were conducted using two different scale physical models, 1:50 and 1:17, within separate rectangular flumes to define scale effects. Flow patterns were analyzed using the Bubble Image Velocimetry (BIV) technique, which tracks air bubbles. The introduction of splitters resulted in a 7% increase in relative energy dissipation. Additionally, the length of inception was reduced to Li/ks = 10, thereby decreasing the potential for subsequent cavitation. Beyond the BIV experiments, two experiments were conducted on the large-scale model using Acoustic Doppler Velocimetry (ADV), with and without splitters, to examine the impact of splitters on the velocity profile above the crest. In the experiment with splitters, the vertical velocity vector (v) contributed to turbulence by changing direction, thereby reducing average velocities both in front of and behind the ogee crest. This led to a reduction in energy on the downstream side of the spillway. Although the small-scale model appears unsuitable for studying two-phase flow, the change in relative energy dissipation from the baseline to the splitter configuration was practically identical for both scale models, thereby supporting the findings of the large-scale model.

Influence of a Modified Weir Profile on Velocity Field and Dissipation Rate in Stepped Spillways: A Comparative Study Using Physical Models and Computational Fluid Dynamics

Influence of a Modified Weir Profile on Velocity Field and Dissipation Rate in Stepped Spillways: A Comparative Study Using Physical Models and Computational Fluid Dynamics

Numerical Investigation of Different Stepped Spillway Geometries over a Mild Slope for Safe Operation Using Multi-Phase Model

Numerical Investigation of Different Stepped Spillway Geometries over a Mild Slope for Safe Operation Using Multi-Phase Model

Comparative Study of Ogee and Stepped Spillway for Enhancement of Energy Dissipation

Comparative Study of Ogee and Stepped Spillway for Enhancement of Energy Dissipation

Self aeration and energy dissipation on a steep stepped chute: how does physical modelling compare to prototype observations?

For the last five decades, a number of overflow stepped chutes were built because the staircase shape is conducive to reduced construction costs and increased rate of energy dissipation. The stepped chute operations are characterised by air‐water flows that are highly turbulent flows with a large rate of energy dissipation, in comparison to smooth chutes. Herein, physical measurements were performed in a large‐size 1 V: 0.80H stepped chute model, with a steep slope typical of modern concrete gravity dams. The results are compared to visual observations of prototype spillway operation under Froude similar conditions. The detailed two‐phase flow measurements were conducted to characterise finely the self‐aeration and air diffusion process downstream of the inception region of free‐surface aeration. The bubble count rate profiles scaled with the instantaneous void fraction variance, and the relationship was biased close to the stepped invert under the influence of large‐scale vortical structures. The rate of energy dissipation was carefully estimated based upon the two‐phase flow measurements and the results are compared to earlier results on similar steep invert slopes and prototype data estimates. At the downstream end of the stepped chute, the rate of energy dissipation ranged from 43 to 46%, i.e. more than twice that on a smooth-invert chute for a similar chute length and discharge range.Graphical abstractCharacteristics of self-aerated stepped chute flows for dc/h = 1.3—(I) Prototype flow at Hinze Dam (Re = 4.0 × 107); (II) Air-water flow properties in the large-size laboratory model (1:15) stepped spillway (Re = 6.1 × 105)

Three-dimensional analysis of the performance of circular stepped spillways in the skimming flow regime

Three-dimensional analysis of the performance of circular stepped spillways in the skimming flow regime

A review of numerical simulations on stepped spillways using the k-ε turbulence model

A review of numerical simulations on stepped spillways using the k-ε turbulence model

Numerical modeling of self-aerated flows: Turbulence modeling and the onset of air entrainment

Numerical modeling of self-aerated flows is essential for understanding water systems and designing hydraulic structures. This work discusses and extends a theoretical/numerical model to represent air entrainment in self-aerated flows, which includes a criterion to define the occurrence of air entrainment, based on a balance between disturbing and stabilizing energies. The impact of the turbulence closure on the modeling of the onset of air entrainment and the distribution of bubble concentration is studied with particular emphasis. This work shows that uniform-density formulations of Reynolds-averaged Navier–Stokes closures lead to severe overprediction of air entrainment due to unphysical transport of turbulent kinetic energy generated in the air phase to the water phase. In contrast, combining variable-density turbulence closures with the energy balance criterion enables accurate prediction of the regions where air is entrained for stepped spillways and plunging jets. The choice of turbulence closure significantly influences the proposed criterion, emphasizing the importance of selecting an appropriate closure for an accurate description of the air entrainment process. Based on the conducted tests, the standard k−ε and buoyancy modified k−ε models better predict the onset of air entrainment and bubble distribution in stepped spillways, while the k−ω SST model proves to be more effective in capturing air entrainment at the impingement point in plunging jets. This study expands the capabilities of numerical models in predicting air entrainment and provides valuable insights into the effects and interrelations of the turbulence modeling, the air entrainment occurrence criteria, and the bubble transport equations.

Flow characteristics and energy dissipation over stepped spillway with various step geometries: case study (steps with curve end sill)

Stepped weirs are used in a wide range of applications, designed to increase energy dissipation. In this study, laboratory experiments were conducted in a flume on six stepped weir models, with a downstream angle of θ = 26.6°. The physical models used were on a scale of 10:1, and tests of discharges up to 0.055 m3/s were carried out. Several step geometries including traditional step, sill and curve geometries were used to study flow behavior and overall energy dissipation. The laboratory investigations were augmented by modelling numerically the within step flow and energy behavior using a 2-D CFD model, incorporating the k-ε model for turbulence closure. The results showed that energy dissipation was greatest for the curved steps by about 10.5%, where it was observed that the skimming flow regime was shifted to a higher discharge range. Numerical modelling results showed good agreement with the experimental results. An inspection of the modelled streamlines highlighted the increase in vortex intensity for the curve model, reflecting the strong circulation observed. The predicted stepwise energy dissipation showed the energy dissipation increase when the step number Ns increases. For the range of step height hs, tested, our results showed that energy dissipation increased with step height. The results from this study can be used to inform engineering design for steps with θ = 26.6° and provide estimates of the expected energy dissipation and residual energy.

The effect of gabion steps on the hydraulic jump characteristics downstream of stepped spillways

ABSTRACT Gabion steps on stepped spillways can be a suitable alternative to solid impermeable steps due to their economic advantages, ease of implementation, stability through water pressure reduction, and energy dissipation. This study explores hydraulic jumps and the rate of energy dissipation downstream of gabion stepped spillways under different flow regimes. Six stepped spillway models, including a solid spillway with solid steps and five models with gabion steps, were made with different step arrangements in a 26.6° slope (1 V:2 H) facility. The results showed that in stepped spillways with gabion steps and in the nappe flow regime, as a result of seepage flow through the pores of the aggregate and overflow passing the gabion step, there is an increased energy dissipation associated with a smaller sequent depth ratio, the relative length of jumps, and roller length compared to solid and impermeable steps. The reduction in the hydraulic jump depends on the flow regime and the arrangement of the gabion steps. For skimming flows, smaller energy dissipation rates were measured downstream of the gabion step. On average, when gabion steps are placed on all steps, the sequent depth ratio, jump length, and roller length decrease by 3.34%, 8.61%, and 8.14%, respectively, compared to solid steps. The maximum energy dissipation was measured at the downstream end of the gabion steps with a value of 74.4%, which is 5.03% more than that with the solid steps. On the solid stepped spillway, the nondimensional residual head was 4.65, and for the same flow conditions, the average dimensionless residual head on the gabion steps was 4.21.

An investigation into the exploratory use of additive manufacturing in stepped spillway model testing in open channel flow

Stepped spillways provide an excellent form of energy dissipation and are used in many locations around the world. Effective designs are crucial in improving protection to downstream erosion and providing economic benefits to the stilling basin design. Additive manufacturing (AM) provides a wide range of possibilities of testing complex and varied geometries in fluid flow research at relatively low cost. This research builds upon previous studies in utilising AM in open channel flow applications. This paper presents a comparative analysis between two types of stepped spillway using preceding weir designs in terms of fluid velocity profile, flow rate, water height upstream and downstream; associated fluid flow parameters and experimental observations. For validation and further analysis, computational fluid dynamics (CFD) modelling is conducted to show close comparisons to the experimental results. Conditions are varied to compare the differences between models being sealed and unsealed, allowing for significant side flow. AM technology allows for cost-effective small models to be created, that can significantly improve the design process for larger scale testing and enhances the field of study for experimental fluid flow research.

Effect of the Stepped Spillway Geometry on the Flow Energy Dissipation

In this research, flume experiments were conducted on stepped weirs to investigate the effect of step shape on the energy dissipation of flow. Four configurations with a constant number of steps were considered, namely, horizontal steps, inclined steps, horizontal steps with rounded sills, and ‎inclined steps with rounded sills. The slopes of inclined steps were 13% and 23%, and the diameters of the rounded sills of the step ends were 10 and 15 cm. The majority of previous studies focused on energy dissipation in stepped weirs in horizontal and inclined steps. In this research, new step geometries were used, such as horizontal steps with rounded sills and inclined steps with rounded sills. Dimensional analysis was applied to correlate the different variables affecting the flow hydraulics. Flow rates in the range of 0.61-9.12 lit/sec were used with each step shape. Results showed that the inclined steps with rounded sills had the highest flow energy dissipation in comparison to the other types. Rounded sills at the end of steps had more effective energy dissipation than did the horizontal step. However, the 23% inclination slope with rounded sills of a 7.5 cm radius was the most effective in dissipating flow energy. Doi: 10.28991/CEJ-2024-010-01-09 Full Text: PDF

Investigation of energy dissipation performance of triangular stepped spillways

Investigation of energy dissipation performance of triangular stepped spillways

Hydrodynamic Loads in a Stilling Basin of a Converging Stepped Spillway: An Experimental Study

This paper presents a methodology for estimation of hydrodynamic loads acting on the bottom and at the walls of a stilling basin of a stepped chute with converging walls, based on the pressure measurements at the selected points of a scale model. This is the first study of hydrodynamic loads for this type of structure, and the first one of the loads on the stilling basin walls in general. For selected flow discharges, step heights and hydraulic jump submergence ratio, the hydrodynamic pressures were measured at a significant number of points, providing the spatio-temporal distribution of relevant hydrodynamic loads. The most influential effect proved to be a convergence angle of the chute walls. Based on these measurements, appropriate regression expressions were proposed for predicting hydrodynamic loads. These expressions show good agreement with measurements, offering a reliable tool for the structural design of stepped spillway stilling basins.