Experimental and numerical evaluation of discharge capacity in piano key weirs

The piano key (PK) weir is a relatively new nonlinear weir geometry that can be used to increase spillway discharge capacity over linear weir geometries, particularly when the weir footprint area is restricted (e.g., spillways on the crest of a concrete dam). The majority of the published PK weir research (e.g., head-discharge curves) has been based on channelized applications (sectional PK weir models in laboratory flumes). The head-discharge characteristics of crest-of-dam PK weir applications are influenced by the approach flow conditions. Using a laboratory-scale physical model, the hydraulic efficiency of a PK weir design was tested with varying approach flow depths, upstream apron slopes, and abutment details. In general, discharge efficiency increased with increasing approach flow depth, steeper approach aprons, and improved abutment geometries that reduced the effects of flow separation.

Submerged flow over various shapes of piano key weir

<p>Many dams around the world are ageing and require upgradation in terms of spillway capacity and other safety aspects. In recent times, challenges faced due to global warming, climate change and cloudburst events have grown not just in numbers but also in extremity. Consequently, several dams and diversion structures are being modified to cope up with the floods resulting from such events. Piano key weir (PKW) has effectively been used in many dam upgradation projects, especially in France and Vietnam, to enhance the discharge capacity of the existing ogee-crested weirs or labyrinth weirs. It has also been used in a diversion scheme in India (Sawra Kuddu). The flow field around a PKW is spatially varied, complex and three-dimensional in nature. The previous researches on PKWs were predominantly focused on the effect of different parameters on its discharging capacity and limited studies are available on the flow field, sediment movement and scouring at PKWs. Considering these gaps, this study was initiated to understand the flow pattern near PKW and its effect on the sediment transport over PKW. Presented here is the experimental work carried out at IIT Roorkee, India on a Type-A PKW flume model with two discharge values, the CFD simulations of those two flow conditions and a comparison between the results. The time-averaged velocity values were measured at different locations in the front of inlet and outlet keys (upto a distance of 0.1 m from the bed level) using a 3D Acoustic Doppler Velocimeter. The simulations were performed in Ansys (academic 19.1) CFX solver using finite volume method, standard k-ε turbulent model, (where k denotes the turbulent kinetic energy and ε is the rate of dissipation of k) and multiphase (volume of fluid) modelling. The experimental results showed an increase in the depth-averaged longitudinal flow velocity towards the inlet, but a decrease in that towards the outlet. A significant rise in the upward velocity (in the outer flow region) towards both the keys was observed experimentally and numerically. Both the approaches also indicated a significant increase in the lateral velocity near the inlet, especially in the inner flow region. CFD simulations clearly showed decelerating and accelerating flow zones in front of the outlet and inlet keys, respectively, and also revealed an accelerating flow over the inlet. However, the velocity profile inside the inlet key could not be measured experimentally, possibly due to flow unsteadiness, high turbulence and flow separation, and it demands further research. The CFD results generally underestimated the velocity values for the measured 0.1 m depth of flow and the mean absolute error values for the resultant velocity were 18.32% and 15.52% for the two discharges, respectively. The rise in the approaching flow velocity components towards the inlet and the sloping key enhance the opportunity of sediment passage over a PKW in comparison to other weirs. Extending this work, the study on the flow field near two-cycles and three-cycles PKW models is undergoing.</p>

Piano key weir is a new type of spillways designed to improve the discharge capacity of dams. Generally, increasing the upstream hydraulic load in piano key weirs results in reduced discharge capacity of the weir. Accordingly, the present study investigated the effects of triangular notch on the discharge coefficient of piano key weirs. The 3D flow field over the piano key weirs was simulated in FLOW-3D software in order to study the flow hydraulics and compare the discharge rates, and the effect of each model on the flow field over the weirs and discharge coefficient was investigated. The results suggested that data of the numerical model were appropriately consistent with that of the laboratory model. According to the results, the discharge coefficient of the triangular piano key weirs was 25% higher than that of the rectangular piano key weirs. It was also observed that changing the notch shape of the piano key weir increased the discharge coefficient of the piano key weir by 36% and 13% for the heights of 5 cm of 7.5 cm, respectively.

Climate change has been affecting significantly dams worldwide, particularly by the accentuation of extreme events. The hydraulic insufficiency of spillways is the most hazardous related risk that directly threatens the dams’ safety. Thus, the Piano Key Weir (PKW) technology may be a cost-effective solution for adapting the spillways of the existing dams and enhancing their resilience against climate change. This paper aims to provide the state of knowledge regarding the climate change issues related to dams with a focus on Morocco. It aims also to assess the cost-effectiveness of implementing the PKW in 27 large Moroccan dams in order to increase the flood release capacity. This work has determined, first, the climate change impacts on water resources and dams, and has discussed the adaptation measures including the implementation of PKW. Then, a detailed case study has been conducted to evaluate the interest of implementing the PKW in Morocco, at the scale of each hydraulic basin, with a comparison to the international experience. Results have revealed that the PKW allows increasing the global discharge capacity of Moroccan spillways by 70%, at a total cost of about 600 MMAD. Souss Massa Draa basin has accounted more than 40% of the total discharge capacity increase, and the best cost-effectiveness values have been identified in Loukkos, Oum Er Rbiaa and Sebou basins. These results may encourage the PKW integration in order to enhance the Climate adaptation and resilience of dams.

This chapter investigates the flow dynamics and energy dissipation of Piano Key Weirs (PKWs) and Labyrinth Weirs (LWs) using Computational Fluid Dynamics (CFD) models. PKWs and LWs are nonlinear weirs designed to enhance discharge capacity and energy dissipation in reservoirs and flood control facilities. Our research employs the FLOW-3D and ANSYS models to analyze various geometric parameters and their effects on discharge performance and energy dissipation. For PKWs, the analysis indicates that trapezoidal PKWs outperform rectangular PKWs regarding discharge efficiency due to their larger inlet flow area and improved flow distribution. Additionally, moving the PKW overhangs toward upstream-zone enhances discharge performance, while moving them toward downstream zone increases energy dissipation. For LWs, the analysis demonstrated that LWs with smaller sidewall angles increase crest length, enhancing discharge performance but leading to early submergence, decreasing the energy dissipation. Finally, it concludes that PKWs and trapezoidal LWs have a new function as structures that dissipate energy near the maximum limit. The findings confirmed the ability of the FLOW-3D and ANSYS models to accurately predict the various flow characteristics. It also provides valuable insights for designing and optimizing PKWs and LWs to balance discharge efficiency and energy dissipation, ensuring the safety and resilience of flood control structures.

A piano key weir (PKW) is a solution for improving the efficiency and safety of reservoirs and simplifying their management. To investigate the influence of the inlet/outlet width ratio on the discharge efficiency of PKWs, a three-dimensional numerical model based on a standard turbulence model and volume-of-fluid (VOF) method is employed, and the flow characteristics of nine laboratory-scale PKWs with different ratios are studied numerically. The results confirm that PKW configurations with are generally superior to those with in terms of discharge capacity. However, as the water head rises, the discharge efficiency of the PKW with a greater decreases more rapidly. By decomposing the total discharge into inlet, lateral and outlet components, according to the flow features of each overflow crest and their contributions to the total discharge, the intrinsic influencing mechanism of on the discharge performance of PKWs is revealed.

The Piano Key Weir (PKW) is a particular geometry of weirs associating with a labyrinth shape and the use of overhangs, which reduce the basis length. The PKW could thus be directly placed on a dam crest. Together with its important discharge capacity for low heads (up to four times that of a Creager weir), this geometric feature makes the PKW an interesting solution for dam rehabilitation. The PKW is a new type of weir, first designed in 2001 and built for the first time in 2006. Even if the first experimental studies confirmed its discharge capacities, there is still a lack of understanding of the flow behaviour upstream, along and downstream from this complex structure. An experimental research, started in 2008 at the Laboratory of Engineering Hydraulics of the University of Liege, will provide contributions to the study of the flow behaviour on large PKW scale models, along with a geometric parameters analysis on models with variable geometries. These studies will enable one to define efficient and scientifically based design rules. This paper presents the strategy and main goals of this four-year study. These goals are also illustrated based on the first results obtained from experiments carried out on large scale models of PKW. The hydraulic behaviour of the structure is clarified based on measurements of water depths, pressures, velocities and discharges on each part of the weir.

The enormous energy carried by discharged water poses a serious threat to the Piano Key Weir (PKW) and its downstream hydraulic structures. However, previous research on energy dissipation in PKWs has mainly focused downstream effects, and the research methods have been largely limited to physical model experiments. To deeply investigate the discharge capacity and hydraulic characteristics of PKW, this study established a PKW model with universally applicable geometric parameters. By combining physical model experiments and numerical simulations, the flow pattern of the PKW, the discharge at the overflow edges, and the variation in the energy dissipation were revealed for different water heads. The results showed that the discharge of the side wall constitutes the majority of the total discharge at low water heads, resulting in a relatively high overall discharge efficiency. As the water head increases, the proportion of discharge from the inlet and outlet keys increases, while the proportion from the side wall decreases. This change results in less discharge from the side wall and a consequent reduction in the overall discharge efficiency. The PKW exhibits superior energy dissipation efficiency under low water heads. However, this efficiency exhibits an inverse relationship with an increasing water head. The overall energy dissipation efficiency can reach 40% to 70%. Additionally, the collision of the water flows inside the outlet chamber and the mixing of the overflow jet play a primary role in energy dissipation. The findings of this study have significant implications for hydraulic engineering construction and PKW operational safety.

Piano key weirs (PKWs) are an improved form of labyrinth weirs, which are becoming popular as a more hydraulically efficient and cost-effective type of weir over its counterparts for both spillway and river flow conditions. More than thirty PKWs are already in construction worldwide, with constructions in India at Swara Kuddu. More than twenty parameters influence the flow over a PKW, and as such, the flow hydraulics near PKW is complex. It is imperative to study the performance of different shapes of PKW to know which shape offers more hydraulically and cost-effective advantages over other shapes. The present study combines the experimental and numerical study of discharge capacity and sediment carrying capacity of the different plan geometries of PKW. The experimental study of the discharging capacity of PKW has been carried out at eighteen discharge points for three plan geometries of PKW. A numerical study using ANSYS FLUENT has also been carried out at five discharges and compared with the experimental results. Vertical velocity near a weir is an essential factor facilitating the uplift of sediment. Sediment profile in the channel has been studied at three discharges experimentally for two types of PKWs: RPKW and TPKW6, all for free-flow conditions. The numerical study has also been carried out at these experimental discharges for studying the vertical component of velocity (v) upstream of PKW. An attempt has been made to isolate critical areas where the sediments are being lifted by the turbulence mechanism, thus helping them pass over the weir. The study shows PKW with a rectangular plan (RPKW) to be more hydraulically efficient than TPKWs with six-degree and thirteen-degree lateral crest variations (TPKW6 & TPKW13). The study also shows RPKW to be more self-cleaning in nature than its trapezoidal counterpart (TPKW6). Numerical study shows a close resemblance to the experimental results with errors well within permissible limits implying its greater use in ascertaining complex flows around hydraulic structures.

Free overfall weirs are hydraulically efficient and reliable in operation. With this, the overfall capacity depends on the hydraulically active developed length of the weir. Folded types of weir, such as the piano key weir (PKW), provide an over-proportionally developed length and are thus especially efficient, in particular for relatively small energy heads. The compact construction of the PKW in addition allows its economic and rapid creation on crest of gravity dams. Therefore, the PKW lends itself if and when the discharge capacity of existing flood spillways is to be increased or in case a subsidiary overflow is to be emplaced under cramped space conditions. The hydraulic functional capability of the PKW has been tested and optimised by means of several model studios. In addition, several PKW have been built and have confirmed their reliability under flood conditions.

Piano key weirs (PKWs) with crown parapet walls effectively manage water levels and maximize storage. However, their efficiency is compromised by interactions between water flow and submerged outlets during rising water levels. This study investigates novel parapet wall designs to improve PKW performance and reduce submergence effects. The experiment focuses on a PKW with a fixed 12.6 cm weir height. Three parapet wall configurations are tested: Mode 1 (walls on all apex), Mode 2 (walls fixed on sides and inlet), and Mode 3 (walls along the sides). Each mode includes three parapet wall profiles: rectangular (consistent form), triangular, and trapezoidal (varying characteristics). Results indicate that parapet wall design significantly affects water level variations with increasing wall height. Mode 3, featuring triangular and trapezoidal parapet walls, demonstrates the highest discharge capacity among the examined profiles. The discharge coefficient correlates with parapet wall height and form. Notably, the triangular wall in Mode 3 outperforms Modes 1 and 2 when parapet walls maintain an R/P ratio of 0.36. This study introduces innovative parapet wall designs to enhance PKW efficiency. By implementing advanced configurations, significant improvements in water control and discharge capacity can be achieved. These findings contribute to the state-of-the-art in PKW technology and offer valuable insights for practical engineering applications.

Piano Key weirs are Labyrinth-like weirs that can be placed on the top of gravity dams. They represent a powerful solution to increase the discharge capacity of existing dam spillways. For proper design, it is necessary to accurately predict this discharge capacity. In this research, artificial neural network and multiple linear and nonlinear regressions are used to set up a new design equation for the discharge capacity of Piano Key weirs. The effect of each parameter on the discharge capacity of Piano Key weirs is tested in these models. Several nondimensional parameters are used to define a functional relationship between the inputs and output. These parameters are built from the geometric dimensions of the structure such as weir height, inlet and outlet keys width, overhangs length, water head, and side crest length. Previous experimental data, which were collected at the experimental laboratory of the research group Hydraulics in Environmental and Civil Engineering (HECE), University of Liege, are used for training and testing patterns of the models. Root mean square errors (RMSE) and coefficient of determination (R) are used as comparing criteria for the evaluation of the models. The model results compare well with experimental results and other existing equations. They also highlight key geometric parameters governing piano key weirs discharge capacity.

Piano Key Weirs are modified version of labyrinth weir with innovation to improve discharging capacity and more compatible for constructing on a existing or new spillway with lesser space requirement and structural stability. The objective of this study was to identify the Piano Key Weir in which the maximum discharge capacity at different UW with p (height of weir) could be achieved. To achieve this for different flow conditions, length magnification ratio (L/W) is taken from 3.56 to 7.40. Also, other parameters are taken in different combinations for getting optimum configuration of Piano Key Weir for better performance. With this in view, three phases of experimental campaign on eighteen Piano Key Weir models are reported in this paper. The ratio (r) of Piano Key Weir to linear weir discharge for a given head was seen to be more than one and found to increase with magnification ratio L/W upto a certain limit of h/p ratio. It was also found that performance of ratio of inlet and outlet cell width was best when two cells were of same width. The analysis of discharge coefficient variation is correlated with h/p.

The Piano Key Weir is a type of labyrinth weir using overhangs to reduce the footprint of the foundation. These are directly placed on a dam crest. Together with its high discharge capacity for low heads, this geometry makes these weirs interesting in dam rehabilitation. However, the Piano Key Weir is a new weir type, first designed in 2001 and built from 2006 by Electricité de France. Even though experimental studies confirmed its appealing discharge capacities, the flow upstream, over and downstream of this complex structure is still not well known. This research presents experimental test results performed on a 1:10 scale model. The experiments aim at determining the flow features along the weir depending on the upstream head. The flow conditions are characterized in terms of specific discharge, velocity, pressure, water level and streamlines along the weir.