Daniel Valero Huerta

Calibration of an Air Entrainment Model for CFD Spillway Applications

Air entrained has become one of the main variables in the study of large spillways performance since it can help avoiding cavitation. Moreover, high rates of air concentration produce significant bulking of the flow as well as a water–solid friction reduction, generating flow acceleration and increasing maximum velocities at the inlet of the energy dissipation structure. Air entrained also affects turbulence inside the flow producing different energy dissipation rates. Aerated spillways physical models are affected by scale effects, with Weber and Reynolds numbers being usually too low to adequately reproduce observed flows. Alternatively, simulation of air–water flows can be carried out by means of Computational Fluid Dynamics techniques in 1:1 scale. However, 3D numerical simulations of spillway flows are time expensive and air–water interfaces need fine resolution meshes which would require extensive computing. Thus, the use of a subgrid scale in air entrainment models can be useful to predict the inception point and the air concentration profile of the flow along the spillway. Computational techniques can handle a more accurate momentum distribution over the spillway sections with affordable costs. In this research, FLOW-3D® routine for turbulent air entrainment is used, coupled with variable density evaluation. VOF and κ-e RNG turbulence model are also employed. Over 200 spillway flow simulations have been carried out to obtain optimal values of the air-entrainment model parameters, which can be used in future spillway simulations. The calibration of the model is carried out employing prototype data. Interesting conclusions are obtained concerning air entrainment model performance.

Numerical investigation of USBR type III stilling basin performance downstream of smooth and stepped spillways

Recent systematic studies on air-water flows have included stepped spillways. However, to date, little has been investigated about how the hydraulic conditions on the stepped spillway may affect the design of traditional energy dissipation structures. In this paper, both smooth chute and stepped chute configurations terminating with the USBR type III stilling basin are tested by means of numerical modelling, allowing a qualitative comparison. Unsteady RANS equations have been employed together with VOF and RNG k-e for free surface tracking and turbulence modeling, respectively. Eight different Froude numbers (F) ranging from 3.1 to 9.5 have been analyzed for a type III basin designed for F = 8, following recent studies conducted in a physical model by Reclamation. The basin flow structure is discussed for both smooth chute and stepped chute cases. Additionally, the modelled basin has been tested for design and adverse hydraulic conditions, obtaining a detailed insight of the role of each basin element and their adapting roles when insufficient tail water conditions exist.

Application of the Optical Flow Method to Velocity Determination in Hydraulic Structure Models

Optical flow estimation is used in Computer Vision for detection of moving obstacles in a sequence of images. The optical flow (OF) is defined as the displacement of brightness patterns between two sequent images. In this paper, this method is applied to high-speed images taken in hydraulic structure models for determination of velocity fields. Water is seeded with tracer particles in two cases and is self-aerated in a third case. It will be shown that the OF method gives valuable results that compare well to other velocity measurements, e.g. by Particle Image Velocimetry. The OF method is generally more time-consuming compared to PIV, but an advantage is given by the density of information when using a so-called global method, as velocity information is obtained at every pixel location.

Hybrid Investigation on the Hydraulic Performance of a New Trapezoidal Fishway

The current study presents a new type of vertical slot fishway. The main difference of this trapezoidal fishway compared to the standard design of a vertical slot fishway remains in the separation of the pools into two zones: the migration corridor and the energy dissipation zone. The structure is first investigated in a physical model to optimize the training walls and slot geometry in order to avoid recirculation of the flow. Velocity and flow depth data from experimental flow measurements is later compared to the three-dimensional numerical model which provides a deeper insight into the flow field. The proposed design is found to avoid large vortices within the migration corridor. Moreover, uniform flow conditions are also found within the energy dissipation zone, thus providing an alternative corridor for fish passage.

Three-dimensional Flow Structure Inside the Cavity of a Non-aerated Stepped Chute

Accurate energy dissipation estimation and improved knowledge on stepped spillways and stepped revetments flow structure may allow safer design of hydraulic and coastal structures. In this study, an ADV Vectrino Profiler has been used to obtain dense observations of the three-dimensional flow structure occurring inside a cavity of 20 cm to 10 cm (length to height) for four flow cases. The obtained friction factors show a strong inverse dependence on the Reynolds number. The displacement length also shows a reduction with increasing Reynolds number, which may indicate that the flow “feels” the cavity more at smaller streamwise velocities. Streamwise and normalwise velocities reveal both a turbulent boundary layer type of flow (upper flow region) and a jet impact and recirculation inside of the cavity. Spanwise median velocities allowed insight on the uncertainty levels of the ADV Vectrino Profiler measurements.

Energy dissipation within the wave run-up at stepped revetments

To understand the processes and energy dissipation performance caused by turbulence during the wave run-up over a stepped revetment, hydraulic model tests with steady flow conditions are conducted and correlated with unsteady flow conditions of the wave run-up within a short time frame. Under irregular waves, the run-up reduction over a stepped revetment is dependent on the Iribarren number and decreases for decreasing Iribarren numbers. Velocity gradients are found to be similar in a steady and unsteady flow regime near the pseudo-bottom.

Interfacial velocity estimation in highly aerated stepped spillway flows with a single tip fibre optical probe and Artificial Neural Networks

Air-water flows can be found in different engineering applications: from nuclear engineering to huge hydraulic structures. In this paper, a single tip fibre optical probe has been used to record high frequency (over 1 MHz) phase functions at different locations of a stepped spillway. These phase functions have been related to the interfacial velocities by means of Artificial Neural Networks (ANN) and the measurements of a classical double tip conductivity probe. Special attention has been put to the input selection and the ANN dimensions. Finally, ANN have shown to be able to link the signal rising times and plateau shapes to the air-water interfacial velocity.