https://popups.uliege.be/ijrewhs2014 fr https://popups.uliege.be/ijrewhs2014/index.php?id=59 The Piano Keys Weir (PK-Weir) represents a new solution which allows increasing weirs capacity (and/or) the capacity storage of the volume water of existing dams. However, the analysis of the geometrical and hydraulic parameters still of research for the improvement of this new type of weir. Different studies and researches made on the PK-Weir were focused on the improvement of the geometrical shape and the studies of the flow of this type of weir. The present work represents a study on the effect of the submergence on the upstream flow of PK-Weir and linear weir. This study is based mainly on the experimentation of the two physical models which is supported by an analysis of the results. Fri, 10 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=59 https://popups.uliege.be/ijrewhs2014/index.php?id=70 Flows over hydraulic structures, such as weirs or spillways, can be modelled using different techniques. New models such as SPH or PFEM are becoming more and more popular. These models are particle and/or meshless and consequently require a lot of computational power. Other methods such as VOF also require a lot of computational time (a few hours). In the frame of 2-D vertical flows, other techniques use much less computation time. For irrotationnal flows, solving the Laplace equation can be done very efficiently. The difficulty of this method lies in the definition of boundary conditions. The free-surface, which is naturally determined when using Lagrangian methods, needs a heavy iterative solving due to its non-linear nature when expressed in the frame of the Laplace equation. This paper will present an original technique that allows a quicker and easier determination of the free-surface. An irregular mesh for boundaries is used and discussed. The method is validated with analytical solutions and experimental measurements. Fri, 10 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=70 https://popups.uliege.be/ijrewhs2014/index.php?id=82 An attraction flow can be used to increase the effectivity of a fish passage. In 2004 a fish passage with a perpendicular attraction flow was built at Oudenaarde (Belgium) on the Upper Scheldt river. The design of the passage was based on scale model tests. In order to evaluate the hydraulic effectivity of the attraction flow, field measurements and new scale model tests are done. Velocities in the attraction flow and the fish passage entrance are assessed quantitatively and data of the scale model tests (1/15) are compared with the field measurements. The measured reach of the attraction flow seems to differ from results of the original scale model tests due to design modifications of the fish passage entrance. Results of the new scale model tests compare well with the data from the field measurements. Based on the results, a re-examination of the basic design rules for the attraction flow and fish pass entrances seems imperative. Fri, 10 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=82 https://popups.uliege.be/ijrewhs2014/index.php?id=92 In this paper the numerical simulations of a free surface flow over a sharp-crested weir are presented and compared to experimental results. The numerical model implemented consists of the meshless Smoothed Particle Hydrodynamics (SPH) method which uses Navier-Stokes equations and the Tait equation of state for water. This numerical method has been developed in the framework of a master thesis and aimed to define the characteristics of the free jet. The validation of the results was performed through the analysis of the pressure field and the comparison of the numerical free surface profiles with experimental measurements conducted in the Hydraulic Laboratory of the University of Liège (ULg). A good qualitative agreement has been obtained. Fri, 10 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=92 https://popups.uliege.be/ijrewhs2014/index.php?id=96 Numerous stepped spillways were built during the last decades. In particular, a stepped spillway may be integrated economically into the downstream face of a RCC gravity dam, or on valley flanks besides embankment or rockfill dams, where slope changes may naturally be implemented due to topography and economic reasons. This paper presents and discusses preliminary results on the air entrainment in the vicinity of an abrupt change chute slope, namely the air concentration distribution and the mean air concentration. A significant influence was observed on the air entrainment pattern, with a decrease of the mean air concentration immediately upstream of the slope change, followed by a marked increase immediately downstream, and a subsequent decrease further down the flatter chute, approaching a practically constant value. Considerable larger air entrainment was observed shortly downstream of the slope change cross-section, in comparison with that found upstream, in the quasi-uniform flow. Fri, 10 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=96 https://popups.uliege.be/ijrewhs2014/index.php?id=149 From the practical point of view, it is usual to install two or more gates in parallel in wide channels. Although it is a very common circumstance in the irrigation networks, there are very few studies to investigate the flow through parallel gates. In this study, two gates installed in parallel were considered. Experiments were then performed to investigate the flow regimes at the downstream of the structure. It was found that for the parallel jets with different discharges as differential opening increased, the gates would be more sensitive to be submerged. This pointed out the role of the interaction between jets, involving momentum exchange and modifications of roller structure. Highly non-uniform velocity distribution was observed by the ADV measurements at the downstream of the parallel gates with a closed side. Also, it was experimentally indicated that when one of the gates was kept closed the tailwater depth value associated with the submergence threshold would depend on the tailwater measuring location from the gate significantly. Wed, 08 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=149 https://popups.uliege.be/ijrewhs2014/index.php?id=168 The results obtained from analytical, numerical and experimental modelling of free-surface vortex flows are presented. Vortex flow in an open channel flow chamber is simulated using the ANSYS CFX steady Eulerian-Eulerian multiphase flow model with various turbulence closure methods. The water surface and tangential velocity profile are also modelled using the Vatistas (n =2) vortex model. These previous techniques are validated using particle tracking velocimetry data obtained from a physical model. Sensitivity analysis carried out on the numerical model presents a case for mesh independence and the results suggest that a structured mesh is essential. Curvature correction makes a significant improvement to the shear stress transport turbulence model. The Reynolds stress model produced the most accurate results; however, it suffers the drawback of computational expense. Errors in the numerical models were found to be in the region of 25% for the water surface and 17% for the tangential velocity. It is concluded that transient modelling is required to further improve the numerical simulation. Comparative results on the water surface and tangential velocity distribution signifies that the Vatistas n =2 model agrees well with physical data. Wed, 08 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=168 https://popups.uliege.be/ijrewhs2014/index.php?id=130 The present work presents a performance comparison between two widely-used CFD codes, namely: the open source platform OpenFOAM and the commercial software FLOW-3D, applied to hydraulic structure modeling. To do so, a case study, consisting of a rectangular channel with a cylindrical bridge pier attached to its rough bottom is modeled using both codes. The flow is assumed to be turbulent transient incompressible multiphase and viscous and is simulated using the finite volume method (FVM) and the volume of fluid approach (VOF). Turbulence is modeled by means of the RANS model RNG k-ε. Two scenarios are considered: the initial situation, where the channel bottom is even, and the equilibrium situation, where it is eroded. The eroded streambed geometry is extracted from laboratory experiments using an open sediment transport channel. Several variables of interest, such as shear stresses and vortex shedding period, are estimated and compared among both numerical models and results available in the literature. The main purpose of this study is to assess the accuracy of these solvers when modeling the hydrodynamics of common sediment transport problems. Wed, 08 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=130 https://popups.uliege.be/ijrewhs2014/index.php?id=185 Interaction between chute blocks and highly aerated flows has been studied in this paper. For this purpose, a RANS model coupled with a calibrated turbulent air entrainment model, VOF method and RNG k - ɛ turbulence model have been employed. This has allowed analysing the complex multiphase flows behaviour in an USBR type II stilling basin with variable chute block height. Furthermore, conducted simulations exhibit some similarities with flow patterns detected in previous B-jump, hydraulic jump and highly aerated flows experimental studies. Finally, it has been also possible to identify two different mechanisms involving the chute blocks effect upon the flow: turbulent rough wall jet and flow deflector. Turbulent wall jet mechanism takes place for lower values of the chute block height and helps to stabilise hydraulic jump for deficient tail water conditions while flow deflector has not shown to be a desirable mechanism in a stilling basin. Wed, 08 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=185 https://popups.uliege.be/ijrewhs2014/index.php?id=177 With liberalization of European market, many high head power plants in Switzerland increase their potential generation to remain competitive. The existing surge tanks have to be modified to keep the flow management constant. A relevant way to limit the time of mass oscillation is to increase head losses at the entrance of a surge tank with an orifice. This study focuses on the influencing parameters of head losses at the entrance of an existing surge tank by a variation of geometry and position between this surge tank and the headrace tunnel. Then, the temporal evolution of head losses is evaluated under unsteady conditions during an emptying of the surge tank Wed, 08 Jul 2015 00:00:00 +0200 https://popups.uliege.be/ijrewhs2014/index.php?id=177