Advances in Hydraulics and Hydroinformatics Volume 2

This Special Issue reports on recent research trends in hydraulics, hydrodynamics, and hydroinformatics, and their novel applications in practical engineering. The Issue covers a wide range of topics, including open channel flows, sediment transport dynamics, two-phase flows, flow-induced vibration and water quality. The collected papers provide insight into new developments in physical, mathematical, and numerical modelling of important problems in hydraulics and hydroinformatics, and include demonstrations of the application of such models in water resources engineering

TWO-DIMENSIONAL HYDRODYNAMIC MODELING OF TWO-PHASE FLOW FOR UNDERSTANDING GEYSER PHENOMENA IN URBAN STORMWATER SYSTEM

During intense rain events a stormwater system can fill rapidly and undergo a transition from open channel flow to pressurized flow. This transition can create large discrete pockets of trapped air in the system. These pockets are pressurized in the horizontal reaches of the system and then are released through vertical vents. In extreme cases, the transition and release of air pockets can create a geyser feature. The current models are inadequate for simulating mixed flows with complicated air-water interactions, such as geysers. Additionally, the simulation of air escaping in the vertical dropshaft is greatly simplified, or completely ignored, in the existing models. In this work a two-phase numerical model solving the Navier-Stokes equations is developed to investigate the key factors that form geysers. A projection method is used to solve the Navier-Stokes Equation. An advanced two-phase flow model, Volume of Fluid (VOF), is implemented in the Navier-Stokes solver to capture and advance the interface. This model has been validated with standard two-phase flow test problems that involve significant interface topology changes, air entrainment and violent free surface motion. The results demonstrate the capability of handling complicated two-phase interactions. The numerical results are compared with experimental data and theoretical solutions. The comparisons consistently show satisfactory performance of the model. The model is applied to a real stormwater system and accurately simulates the pressurization process in a horizontal channel. The two-phase model is applied to simulate air pockets rising and release motion in a vertical riser. The numerical model demonstrates the dominant factors that contribute to geyser formation, including air pocket size, pressurization of main pipe and surcharged state in the vertical riser. It captures the key dynamics of two-phase flow in the vertical riser, consistent with experimental results, suggesting that the code has an excellent potential of extending its use to practical applications

Current state and future trends in boundary layer control on lifting surfaces

Successful flow control may bring numerous benefits, such as flow stabilization, flow reattachment, separation delay, drag reduction, lift increase, aerodynamic performance improvement, energy efficiency increase, shock delay or weakening, noise reduction, etc. For these purposes, many different flow control devices, which can be classified as passive, semi-active and active, have been designed and tested. This review paper aims to highlight the most promising and commonly employed boundary layer control methods as well as outline their potential in specific applications in aerospace and energy engineering. Referenced studies, performed on various geometries (flat plates, channels, airfoils, wings, blades, cylinders), are primarily numerical or experimental. Although enhanced aerodynamic performance is achieved in many cases, further research is required to draw general conclusions. This paper aims to demonstrate that, in the future, we may expect further developments of flow control actuators, as well as their increased application

CFD modelling of dam spillway aerator

The purposes of this master thesis are the simulation of the aerator air flow driven by the spillway water flow in the Bergeforsen dam and the behavior of the flow in the stilling basin. Aerators are employed to supply air at critical locations in the flow where low pressure and cavitation may occur in order to protect the structure. The simulations were carried out, first in 2D and then in 3D, with the software FLUENT/GAMBIT describing the spillway and the stilling basin. Results were mainly concentrate on the interface between phases, air entrainment but also velocity and pressure of the flow. Limited data from laboratory experiments were available; however, their usefulness might be limited due to scale effects occurring in such two-phase flow problems

Radar Sub-surface Sensing for Mapping the Extent of Hydraulic Fractures and for Monitoring Lake Ice and Design of Some Novel Antennas.

Hydraulic fracturing, which is a fast-developing well-stimulation technique, has greatly expanded oil and natural gas production in the United States. As the use of hydraulic fracturing has grown, concerns about its environmental impacts have also increased. A sub-surface imaging radar that can detect the extent of hydraulic fractures is highly demanded, but existing radar designs cannot meet the requirement of penetration range on the order of kilometers due to the exorbitant propagation loss in the ground. In the thesis, a medium frequency (MF) band sub-surface radar sensing system is proposed to extend the detectable range to kilometers in rock layers. Algorithms for cross-hole and single-hole configurations are developed based on simulations using point targets and realistic fractured rock models. A super-miniaturized borehole antenna and its feeding network are also designed for this radar system. Also application of imaging radars for sub-surface sensing frozen lakes at Arctic regions is investigated. The scattering mechanism is the key point to understand the radar data and to extract useful information. To explore this topic, a full-wave simulation model to analyze lake ice scattering phenomenology that includes columnar air bubbles is presented. Based on this model, the scattering mechanism from the rough ice/water interface and columnar air bubbles in the ice at C band is addressed and concludes that the roughness at the interface between ice and water is the dominate contributor to backscatter and once the lake is completely frozen the backscatter diminishes significantly. Radar remote sensing systems often require high-performance antennas with special specifications. Besides the borehole antenna for MF band subsurface imaging system, several other antennas are also designed for potential radar systems. Surface-to-borehole setup is an alternative configuration for subsurface imaging system, which requires a miniaturized planar antenna placed on the surface. Such antenna is developed with using artificial electromagnetic materials for size reduction. Furthermore, circularly polarized (CP) waveform can be used for imaging system and omnidirectional CP antenna is needed. Thus, a low-profile planar azimuthal omnidirectional CP antenna with gain of 1dB and bandwidth of 40MHz is designed at 2.4GHz by combining a novel slot antenna and a PIFA antenna.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120674/1/wujf_1.pd

Effect of polymer additives on transitioning and turbulent boundary layers

Injection of small quantities of polymer solutions in various internal and external turbulent flows can produce a substantial reduction of skin friction drag. This phenomenon, known as Toms phenomenon, has been actively studied in the past few decades and applied in various industrial flows to increase efficiency, decrease operating costs, and reduce emissions. A number of previous numerical studies have hypothesized that the long chains of polymer molecules interact with various turbulent motions thereby decreasing the turbulent fluctuations and reducing skin friction. The experimental investigations conducted in the present work provide a comprehensive understanding of the development of a polymer drag reduced boundary layer flow while providing critical insights into the polymer-turbulence interactions in both turbulent and bypass transitioning boundary layers. The outcomes are particularly applicable for the practical implementation of this flow control strategy on marine vehicles. The experiments are conducted in a specialized water tunnel facility by means of particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) in a flat-plate boundary layer injected with polymer solutions via a tangentially inclined two-dimensional slot. The drag reducing effect of the heterogeneously distributed polymers on the flow development is characterized by contrasting the results against the baseline flow of water in each case. Critical questions with regards to the effect of the polymer concentration on the drag reduction performance in turbulent boundary layers are first addressed by considering three different concentrations of polyethylene oxide (PEO) covering a wide range of the drag reduction regime. The analysis of velocity and concentration measurements provides a link between the local polymer concentration, flow development, and achieved drag reduction. The changes in the slope of the logarithmic region of the velocity profiles are associated with various sub-regimes of drag reduction providing insights into the dominance of the viscous and inertial effects within the respective sub-regimes, which are important for the understanding of the ultimate limit of drag reduction. Further investigations are conducted using three-dimensional PIV measurements in the buffer and lower log regions of a drag reduced boundary layer, which elucidate the effect of polymer injection on various coherent structures in this region. The polymers are noted to dampen the turbulence producing motions, such as ejections and sweeps, which is illustrated through conditionally averaged flow fields. Accordingly, the Reynolds shear stress, a measure of turbulence production, is observed to be reduced in both cores of the structures and around the quasi-streamwise vortices, presenting an effect expected due to various viscoelastic mechanisms. The same trend is also observed to varying degrees within other frequently occurring coherent structures which are associated with the low-speed streaks, such as hairpin-like vortices, meandered streaks, and the precursors of streak breakdown events, confirming the importance of the polymer-turbulence interactions in turbulence control with this technique. The detailed planar and tomographic PIV measurements are further utilized for the characterization of extreme skin friction events which are largely associated with the low and high-speed streaks. Conditional averaged flow fields corresponding to the extreme events elucidate the polymer effect on the associated topology of the near-wall flow surrounding these events while signifying the dampening of large structures of Reynolds shear stress formed within the buffer layer. Further, a scale decomposition based analysis elucidates the effect of polymers on various length scales which are directly associated with the reduction in the Reynolds shear stress. The scale-decomposed conditional flow fields are further utilized to establish a quantitative measure of the association of the near-wall Reynolds shear stress with the skin friction, highlighting the effect of polymer injection on the phase differences between these quantities. Considering the substantial effects of the polymers particularly on the turbulence producing coherent structures, the effect of polymers on the transitional-turbulent motions within a bypass transitioning boundary layer are investigated using both planar PIV and PLIF. The effect of polymer injection is observed to accelerate the transition process in comparison to the baseline Newtonian flow depending on the location of injection with respect to a trip-wire. The acceleration of the transition process is observed via the increase in the amplification of velocity perturbations in the early transition stages which are dominated by Kelvin-Helmholtz instabilities. Characterization of the resulting flow development illustrates important differences in the trends of flow statistics and skin friction, highlighting the advantages and drawbacks of polymer injection within the transitional regime of the boundary layer

Wind Action Phenomena Associated with Large-Span Bridges

In the past, the design of bridges over increasing distances was limited by construction techniques and, as always, by economics. As technological advances have turned possible cable-supported bridges of incredible spans, a new challenge has been added to the equation: that of withstanding the action of winds without developing undesirable dynamic responses. In this chapter, the several aerodynamic phenomena of relevance to long-span bridges are classified and discussed. This will interest both experts and non-experts in the field, thanks to the overview that is given. For certain cases, codes of practice recommend wind tunnel tests. The reader is introduced to these, as well as to numerical simulations, which are currently gaining increasing importance. Next, measures for attenuating susceptibility for undesirable dynamic responses are reviewed. The chapter ends with a discussion of the Vila Real Bridge deck section, based on wind tunnel tests and numerical simulations carried out by the authors: the aerodynamics was effectively improved with geometrically subtle modifications that were proposed and adopted still in the design phase