Daniel ValeroKarlsruhe Institute of Technology | KIT · Institute of Water and River Basin Management
Daniel Valero
Doctor of Philosophy
Research Associate (KIT);
Senior Lecturer/Researcher in Hydraulic Engineering (IHE Delft)
About
54
Publications
17,072
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848
Citations
Citations since 2017
Introduction
My main expertise is related to turbulent multiphase flows, which occur both in water infrastructure and river flows; including: air-water, water-sediment and plastic-water flows.
Additional affiliations
January 2019 - present
November 2014 - December 2018
Publications
Publications (54)
A new formulation for the prediction of free surface dynamics related to the turbulence occurring nearby is proposed. This formulation, altogether with a breakup criterion, can be used to compute the inception of self-aeration in high velocity flows like those occurring in hydraulic structures. Assuming a simple perturbation geometry, a kinematic a...
Air–water flow turbulence was derived from pseudo-instantaneous velocities measured with a dual-tip phase-detection probe. This new technique is proposed based upon adaptive time windows for cross-correlation analysis combined with robust filtering criteria, allowing computation of velocity time series in highly aerated flows. Each velocity estimat...
Gas–liquid flows occur in many natural environments such as breaking waves, river rapids and human-made systems, including nuclear reactors and water treatment or conveyance infrastructure. Such two-phase flows are commonly investigated using phase-detection intrusive probes, yielding velocities that are considered to be directly representative of...
Turbulence is ubiquitous in river flows and it is determinant for many fluvial processes such as channel morphology evolution, conservation of ecosystems and maintenance of water quality. Although a well settled theoretical frame regarding fundamentals of turbulent flows exists, the interdependencies between turbulence and river geomorphology mecha...
Current riverine plastic monitoring best practices mainly consider surface observations, thus neglecting the underlying distribution of plastics in the water column. Bias on plastic budgets estimations hinders advances on modelling and prediction of plastics fate. Here, we experimentally disclose the structure of plastics transport in surface water...
Microplastic (MP) pollution is a well document threat to our aquatic and terrestrial ecosystems, however, the mechanisms by which MPs are transported in river flows are still unknown. The transport of MPs and natural sediment in aquatic flows could be somewhat comparable, as particles are similar in size. However, it is unknown how the lower densit...
For millennia, societal progress, health and prosperous economic growth has been closely linked to development of water infrastructure. Now in the 21st century, humankind faces some immense challenges including increasing and migrating populations, water and food security, damaged ecosystems, and a growing energy crisis, all coupled with the effect...
Bank erosion in riverine systems is one of the most complex, yet rampant, morphodynamic processes with significant implications for riparian activities and thereby the population. Therefore, it is an important aspect of the geomorphological evolution of a river reach that must be taken into consideration by river engineers while planning training,...
Gravity currents are relevant environmental flows, present in maritime and coastal applications, river hydraulics, and atmospheric flows. Their impacts on natural and human systems are substantial provided that they are able to transport large amounts of mass at large velocities and distances. Computational Fluid Dynamics (CFD) can be a valuable al...
Shallow flows are common in natural and human-made environments. Even for simple rectangular shallow reservoirs, recent laboratory experiments show that the developing flow fields are particularly complex, involving large-scale turbulent structures. For specific combinations of reservoir size and hydraulic conditions, a meandering jet can be observ...
Although the study of microplastics in the aquatic environment incorporates a diversity of research fields, it is still in its infancy in many aspects while comparable topics have been studied in other disciplines for decades. In particular, extensive research in sedimentology can provide valuable insights to guide future microplastics research. To...
Shallow flows are common in natural and human-made environments. Even for simple rectangular shallow reservoirs, recent laboratory experiments show that the developing flow fields are particularly complex, involving large-scale turbulent structures. For specific combinations of reservoir size and hydraulic conditions, a meandering jet can be observ...
This study explores the morphodynamic impact of groups of piers with different configurations (i.e., span characteristics, number of piers, and different reach locations) in a river cross section. It focuses on sandy low-land rivers presenting steady alternate bars and low Froude numbers. A 2DH (vertically integrated) numerical physics-based model...
Hydraulic structures have supported the development of societies for millennia
and continue to be an integral part of global water infrastructure. Engineering
of these important pieces of water infrastructure requires a specialised understanding
of how water interacts with the structure to ensure maximum safety
and functionality. With sustainabilit...
Wall shear stress modification in self-aerated flows has been observed in boundary layer type flows mainly in the form of drag reduction. Due to its complexity, drag reduction has predominantly been studied using experimental techniques and empirical analyses, whereas the development of conceptual approaches is limited. In this study, two-phase ope...
Water-related problems affect several billion people’s lives and represent an annual challenge assessed at multitrillion US dollars, which substantiates their core role in the UN Sustainable Development Goals. Preventing direct and indirect impacts associated with water excess or water scarcity events requires expert judgement based on reliable inf...
Measuring flow depths in free-surface turbulent flows can be challenging due to their fast dynamics and the presence of aeration. This study analyses the suitability of a low-cost sensor, the Intel® RealSense™ D435 RGB-D camera, for characterization of a highly aerated case study: the hydraulic jump. As with all instrumentation, special care must b...
Robust estimators are parameters insensitive to the presence of outliers. However, they presume the shape of the variables' probability density function. This study exemplifies the sensitivity of turbulent quantities to the use of classic and robust estimators and the presence of outliers in turbulent flow depth time series. A wide range of turbule...
Dual-tip phase-detection intrusive probes are the most widely used experimental technique for measuring interfacial velocities in highly aerated flows. Recently, we have introduced an adaptive window cross-correlation (AWCC) technique, which allows for the estimation of pseudo-instantaneous velocities and associated velocity statistics. Several pot...
Dual-tip phase-detection intrusive probes are commonly used to characterize gas-liquid flow velocities in
hydraulic structures. Traditional post-processing is based upon the cross-correlation analysis of the raw voltage
signals of the two probe tips, providing a time-averaged velocity for the full sampling duration. A recent
advancement of the trad...
Hydraulic jumps are oftentimes encountered in natural and human-made environments. The transition from supercritical to subcritical flow involves large energy dissipation rates and substantial air entrainment, preventing the use of monophasic flow measurement instrumentation. This paper presents an experimental study of a stable hydraulic jump with...
Dual-tip phase-detection probes can be used to measure flow properties in gas-liquid flows. Traditionally, time-averaged interfacial velocities have been obtained through cross-correlation analysis of long time-series of phase fraction signals. Using small groups of detected particles, a recently developed adaptive window cross-correlation (AWCC) t...
Hydraulic jumps are oftentimes encountered in natural and human-made environments. The transition from supercritical to subcritical flow involves large energy dissipation rates and substantial air entrainment, preventing the use of monophasic flow measurement instrumentation. This paper presents an experimental study of a stable hydraulic jump with...
The writers appreciate the discussers' interest in this paper and agree that further research is needed if standardized design guidelines are to be developed to account for the effects of a stepped chute invert on hydraulic jump stilling basin performance. This was indeed the ultimate motivation of the original paper. The writers are grateful for t...
Dual-tip phase-detection probes can be used to measure flow properties in gas-liquid flows. Traditionally, time-averaged interfacial velocities have been obtained through cross-correlation analysis of long time-series of phase fraction signals. Using small groups of detected particles, a recently developed adaptive window cross-correlation (AWCC) t...
Highly turbulent free-surface flows are often characterized by air entrainment, resulting in considerable flow bulking and a modulation of energy dissipation. An understanding of air-water flows remains constrained by instrumentation limitations, scale effects and few analytical developments. Whereas past attempts have addressed air-water flow rese...
With climate change all over the mass media and the United Nations’ Sustainable Development Goals as a target, water problems remain in the spotlight and progress seems partly – if not completely – conditioned by water-related issues. An unprecedented transformation of our sector appears to be awakening and advances should come through the producti...
Hydraulic jumps are oftentimes encountered in natural and human-made environments. The transition from supercritical to subcritical flow involves large energy dissipation rates and substantial air entrainment, preventing the use of monophasic flow measurement instrumentation. This paper presents an experimental study of a stable hydraulic jump with...
Robust estimators and different filtering techniques are proposed and their impact on the determination of a wide range of turbulence quantities is analysed. High-frequency water level measurements in a stepped spillway are used as a case study. The studied variables contemplated: the expected free surface level, the expected fluctuation intensity,...
During the past two decades, hydraulic jumps have been investigated using Computational Fluid Dynamics (CFD). The second part of this two-part study is devoted to the state-of-the-art of the numerical simulation of the hydraulic jump. First, the most widely-used CFD approaches, namely the Reynolds-Averaged Navier–Stokes (RANS), the Large Eddy Simul...
Hydraulic jumps have been the object of extensive experimental investigation, providing the numerical community with a complete case study for models' performance assessment. This study constitutes an exhaustive literature review on hydraulic jumps' experimental datasets. Both mean and turbulent parameters characterising hydraulic jumps are compreh...
This dissertation is organized in five parts. Part I is made of four chapters which aim to introduce this dissertation and put it in the context of past developments. In Chapter 1, a historic analysis of air-water flows research in open channel flows is presented, jointly with a detailed discussion on research trends. Besides, aims and scope of thi...
As with most high-velocity free-surface flows, stepped spillway flows become self-aerated when the drop height exceeds a critical value. Due to the step-induced macro-roughness, the flow field becomes more turbulent than on a similar smooth-invert chute. For this reason, cascades are oftentimes used as re-aeration structures in wastewater treatment...
New information regarding the influence of a stepped chute on the hydraulic performance of the United States Bureau of Reclamation (Reclamation) Type III hydraulic jump stilling basin is presented for design (steady) and adverse (decreasing tailwater) conditions. Using published experimental data and computational fluid dynamics (CFD) models, this...
A new methodology is proposed to spatially filter acoustic Doppler velocimetry data from a Vectrino profiler based on the differential mean velocity equation. Lower and upper bounds are formulated in terms of physically based flow constraints. Practical implementation is discussed, and its application is tested against data gathered from an open-ch...
Accurate determination of free-surface dynamics has attracted much research attention during the past decade and has important applications in many environmental and water related areas. In this study, the free-surface dynamics in several turbulent flows commonly found in nature were investigated using a synchronised setup consisting of an ultrason...
Interest in air-water flows has increased considerably for the last decades, being a common research field for different engineering applications ranging from nuclear engineering to large hydraulic structures or water quality treatments. Investigation of complex air-water flow behavior requires sophisticated instrumentation devices, with additional...
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 rev...
Present literature on air-water flows is briefly reviewed, including articles of the main five international Journals published along the last four years. Main advances in the most fruitful topics related to air entrainment are discussed. Main areas of interest are: stepped spillways, bubbles in pipe flows, numerical modelling and instrumentation
Environmental discharges have been traditionally designed by means of cost-intensive and time-consuming experimental studies. Some extensively validated models based on an integral approach have been often employed for water quality problems, as recommended by USEPA (i.e.: CORMIX). In this study, FLOW-3D is employed for a full 3D RANS modelling of...
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. Wat...
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 II...
A comparative performance analysis of the CFD platforms OpenFOAM and FLOW-3D is presented, focusing on a 3D swirling turbulent flow: a steady hydraulic jump at low Reynolds number. Turbulence is treated using RANS approach RNG k-ε. A Volume Of Fluid (VOF) method is used to track the air–water interface, consequently aeration is modeled using an Eul...
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 veloci...
Optical flow estimation is known from Computer Vision where it is used to determine obstacle movements through a sequence of images following an assumption of brightness conservation. This paper presents the first study on application of the optical flow method to aerated stepped spillway flows. For this purpose, the flow is captured with a high-sp...
Self-aeration is traditionally explained by the water turbulent boundary layer outer edge intersection with the free surface. This paper presents a discussion on the commonly accepted hypothesis behind the computation of the critical point of self-aeration in spillway flows and a new formulation is proposed based on the existence of a developing ai...
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...
In stepped spillway flows, a self-aerated flow region is often found where large quantities of air may be entrained into the water body. This air is then mixed with the water phase leading to an air-water mixture flow with different characteristics than the clear water flow. Thus, air entrainment is an important flow feature which needs to be consi...
In this study, different preprocessing techniques have been applied in order to test if the accuracy of Bubble Image Velocimetry (BIV) calculations in self-aerated flows can be improved. For this purpose, high-speed movies with a resolution of 1920 × 1200 px and a frame rate of 730 Hz are captured on a stepped spillway model with a Phantom M120 cam...
![Figura 1: El funcionamiento del EcoSphere ([11]).](profile/Lluis-M-Garcia-Raffi/publication/273339125/figure/fig1/AS:391788230660097@1470421001281/Figura-1-El-funcionamiento-del-EcoSphere-11_Q320.jpg)
This article is the result of the work developed by students in the subject “Introducción a las Técnicas de Modelización Matemática" at School of Civil Engineering in Valencia. The topic was proposed by one of the students and its development has been done in the classroom throughout working sessions, seminar and discussion sessions. All of the stu...
Projects
Projects (6)
Patricia is investigating the formation of turbidity currents by an impinging 2D water jet. The core of her research is experimental, and she approaches the problem from a hydraulic and fluid mechanics point of view. She hopes her PhD research will contribute to a more sustainable management of sedimentation processes in key hydraulic infrastructures (such as water reservoirs).
