Experimental and Theoretical Study of the Characteristics of Submerged Horizontal Gas Jets and Vertical Plunging Water Jets in Water Ambient

En este estudio se han construido dos diferentes instalaciones para investigar primero los chorros de gas horizontales y en segundo lugar los chorros verticales de agua que impactan sobre superficies libres de fluido, también se ha desarrollado un modelo numérico integral para predecir las trayectorias de estos jets y sus parámetros más importantes, validándose con los resultados experimentales obtenidos. En la primera parte de este trabajo, se han realizado experimentos para investigar el comportamiento de chorros de gas horizontales penetrando en agua. Los resultados experimentales indicaron que la longitud de penetración de los chorros de gas está fuertemente influenciada por el diámetro de la boquilla y el número de Froude, así como con el flujo de masa de de entrada y su momento. Aumentar el número de Froude y el diámetro del inyector lleva a aumentar la inestabilidad de jet. Además, la máxima ubicación antes de jet pinch-off se muestra que mantiene una relación logarítmica con el número de Froude para todos los diámetros de jet. Se han desarrollado correlaciones empíricas para predecir estos parámetros. Se ha desarrollado un modelo basado en la integración de las ecuaciones de conservación para que resulte útil en el diseño de aplicaciones en las que participen chorros horizontales así como para asistir a la investigación experimental. Las predicciones del modelo integral se comparan con los datos de los datos experimentales obtenidos con muy buenos resultados. En la segunda parte de este trabajo, se realizaron una serie de experimentos con de chorros de agua, inyectados verticalmente hacia abajo, a través de toberas circulares que impactan sobre una superficie de agua. Los resultados obtenidos mostraron que la profundidad de penetración de la burbuja disminuye con la longitud del chorro, pero que después de ciertas condiciones se mantiene casi constante. Además ésta aumenta con los diámetros de la boquilla y la velocidad del chorro. La velocidad de arrastreHarby Mohamed Abd Alaal, K. (2012). Experimental and Theoretical Study of the Characteristics of Submerged Horizontal Gas Jets and Vertical Plunging Water Jets in Water Ambient [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18065Palanci

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

New Advances of Cavitation Instabilities

Cavitation refers to the formation of vapor cavities in a liquid when the local pressure becomes lower than the saturation pressure. In many hydraulic applications, cavitation is considered as a non-desirable phenomenon, as far as it may cause performance degradation, vibration problems, enhance broad-band noise-emission, and eventually trigger erosion. In this Special Issue, recent findings about cavitation instabilities are reported. More precisely, the dynamics of cavitation sheets are explored at very low Reynolds numbers in laminar flows, and in microscale applications. Both experimental and numerical approach are used. For the latter, original methods are assessed, such as smooth particles hydrodynamics or detached eddy simulations coupled to a compressible approach

Acoustics-turbulence interaction

An investigation of the instability frequency was undertaken. Measurements revealed that the hot wire probe induces and sustains stable upstream oscillation of the free shear layer. The characteristics of the free shear layer tone are found to be different from the slit jet wedge edgetone phenomenon. The shear tone induced by a plane wedge in a plane free shear layer was then examined in order to further document the phenomenon. The eigenvalues and eigenfunctions of the tone fundamental show agreement with the spatial stability theory. A comprehensive summary of the results is also included

Thermo-fluid-dynamics of impinging swirling jets

The superimposition of a tangential motion on a conventional round jet has been demonstrated to significantly affect the large-scale topology of the flow. Swirling flows are widely employed, in the impinging configuration, in several industrial processes which involve both non-reacting and reacting applications. In the present dissertation, the simultaneously acquired thermal and three-dimensional velocity fields of an impinging hot jet emerging from a custom swirl generator in a cold ambient are presented. The velocity and temperature fields are experimentally measured using time-resolved Tomographic PIV and high-speed Infrared thermography in a combined system. A detailed description of a custom swirl generator is provided, and the time-averaged velocity profiles of a free swirling flow are discussed in order to estimate the swirl number. The instantaneous three-dimensional dynamics in proximity of the nozzle is discussed and the main features of a free swirling jet are investigated through the application of Proper Orthogonal Decomposition technique. The time-dependent features of velocity and temperature fields of an impinging swirling jet are investigated through the description of the time sequences of the temperature fluctuations and the synchronised instantaneous vortical structures. Taking advantage of the simultaneous acquisition and of the knowledge of the relative positioning of thermal and velocity frames, two different correlation techniques are applied, and their outcomes discussed

Swirl and precession in submerged free and confined jets

The present thesis deals with an experimental investigation on swirl and precession in free and confined submerged jets in cold flow conditions by means of tomographic particle image velocimetry. Swirling and precessing jets are widely used to enhance the mixing performance in combustion applications. Therefore, the aim of the present research is devoted to elucidate insights on the 3D flow patterns of swirling flows characterized by either a periodic-stable precessing helical structures or intermittent bi-stable fluidic mechanism that produces a large scale precessing motion. To this purpose, a lean pre-vaporized premixed swirl injector is characterized through the study of its main flow features generated in free and confined configurations. Whereas, a fluidic precessing jet nozzle is undertaken to inspect the flow features characteristics of the precessing motion. Moreover, the precessing jet has been investigated for two inflow conditions using either a short-pipe nozzle, i.e., jet without grid, or placing a regular grid at the inlet. The flow features in swirling and precessing jets so generated are described in the thesis

Micro injection fuel/air premixer/combustion

Lean premixed (LP) combustion has become the dominant industrial approach to reduce NOx emissions. Homogeneous mixing of lean fuel and air mixtures prevents the presence of undesirable localized regions of near-stoichiometric fuel/air mixtures, thereby allowing a reduction in thermal NOx. A new concept, a multi-point micro injection premixer, is presented in this dissertation. The multi-point micro injection premixer is a porous plate that provides a simple but extremely effective method to mix air and fuel. An array of fuel jets is injected in a direction perpendicular to the plane of the premixer plate into an oncoming counterflow stream of air. The fuel mixes with the air, and reverses direction. The mixture of air and fuel travels back through the injector plate exiting as an extremely uniform mixture. A simplified numerical model was built to analyze the case of a single micro counterflow jet mixing into on an oncoming air stream. The model predicted that a higher fuel/air momentum ratio results in better mixing. Four injection plates are fabricated with different combinations of hole arrays and hole diameters. The velocity measurement by constant temperature anemometer showed that all jets in a premixer have similar jet velocity profiles. Velocity profiles were taken near the dump plane of the combustor for a variety of cases. It was found that the presence of the premixer plate had very little effect on the macroscopic velocity distribution. However, with counter-injection, the turbulence intensity was much greater across the core region exiting the premixer, and less near the periphery (compared to the case without counter-injection). From combustion experiments, it is found that at same fuel and air mass flow rates, the cases where a micro injector was used to mix air and fuel produced lower equivalence ratio at LBO, higher heat release rate and lower NOx emission than the cases without counter injection. Furthermore, the higher the counterflow jet velocity, the better the combustion performance. From all the experiment data it is shown that the new concept multi-point micro injection premixer provides very good mixing of fuel/air with high efficiency

Engineering Fluid Dynamics 2019-2020

This book contains the successful submissions to a Special Issue of Energies entitled “Engineering Fluid Dynamics 2019–2020”. The topic of engineering fluid dynamics includes both experimental and computational studies. Of special interest were submissions from the fields of mechanical, chemical, marine, safety, and energy engineering. We welcomed original research articles and review articles. After one-and-a-half years, 59 papers were submitted and 31 were accepted for publication. The average processing time was about 41 days. The authors had the following geographical distribution: China (15); Korea (7); Japan (3); Norway (2); Sweden (2); Vietnam (2); Australia (1); Denmark (1); Germany (1); Mexico (1); Poland (1); Saudi Arabia (1); USA (1); Serbia (1). Papers covered a wide range of topics including analysis of free-surface waves, bridge girders, gear boxes, hills, radiation heat transfer, spillways, turbulent flames, pipe flow, open channels, jets, combustion chambers, welding, sprinkler, slug flow, turbines, thermoelectric power generation, airfoils, bed formation, fires in tunnels, shell-and-tube heat exchangers, and pumps

Evaporating crossflow sprays in gas-solid flows

Injection of evaporating sprays into gas-solid flows is encountered in many engineering processes such as energy production industry and chemical industry. The phenomenon involves phase change, three-phase interactions, heat and mass transfer. All of these characteristics control the process efficiency, pollutant production and product quality. However, very limited studies are available on the evaporating spray jets in gas-solid flows, especially on the spray evaporation rate within a gas-solid medium. A combined study of experiments and theoretical analysis has been carried out here to investigate the fundamental mechanism of evaporating Crossflow spray jets in gas-solid flows. In this study, in addition to a laboratory scale circulating fluidized bed to provide a continuous gas-solid flows, a laser/lamp-light assisted visualization and image analysis system and a computer aided temperature measurement system have been developed which enables measurement of spray trajectories and temperature distributions of mixture phases in dilute/dense gas-solid flows. All the experiments have been performed in the circulating fluidized bed with a simple rectangular column, controllable solids load and flow conditions, and well-defined liquid nitrogen sprays. The spray trajectory, spray penetration length, and flow pattern are investigated. The geometric and operating parameters, such as nozzle size, nozzle type, injection angle, jetting velocity, and solids loading are studied in the experiments. The experimental study shows that the loading of solid particles in mainstream can significantly shorten the penetration length and alter the spray structure. It is also shown that the quick evaporation of spray droplets leads to the dilution of solids concentration in the evaporation region as well as the reduction of phase temperatures. In this study, a fundamental parametric model for applications of an evaporating liquid jet into a gas-solid flow, which takes into account the three-phase interactions as well as phase changes. The model is focused on the study of the effects of spray parameters on the mixing characteristics such as spray penetration length, temperature and velocity of each phase, trajectories, and the phase volume fraction distributions. The governing equations are based on the conservation principles of mass, momentum and energy of all three phases. The model predictions have also been found in good agreement with the experimental results. Droplet evaporation rate is the most important factor to affect the phase interactions of the spray in gas-solid flows. The spray evaporation is dominated by the heat transfer through collisions between droplets and solid particles. Part of this study is focused on the Leidenfrost collisions between evaporating droplets and solid particles, which are involved in many multiphase flow applications, e.g., petroleum refinery, surface coating, and fire quenching. In this study, an analytical model has been developed to describe the Leidenfrost collision between a droplet and a hot solid sphere. The whole collision process, the maximum collision time, the maximum deformation area, and the evaporation rate are simulated. Effects of solid curvature and Weber number on the collision time and droplet evaporation rate are illustrated. Modeling predictions are validated by the available experimental results