The bubble formation and coalescence phenomena above submerged nozzles having diameters between 1 and 7 mm were studied visually in a stagnant water column. Air was supplied at the nozzles under constant flow rate conditions and the field of view extended from the nozzle exit up to 14 cm above it. The air Reynolds number based on the nozzle diameter covered a range between 50 and 40000. The study was focused on a unified description of the bubbling phenomena, beginning from the single bubble formation up to the jet formation, and the transitions between the various bubbling regions. It was concluded that for nozzles, as injector devices and for the aidwater system investigated, the Reynolds number is the controlling variable for the bubbling phenomena above the nozzles and for the transition between the various bubbling regions.Les phenomenes de formation et de coalescence des bulles au-dessus d'orifices submerges dont le diametre est compris entre 1 et 7 mm ont ete etudies visuellement dans une colonne d'eau stagnante. Les orifices sont alimentes en air a debit constant et la hauteur du champ d'etude est de 14 cm a partir de la sortie de I'orifice. Le nombre de Reynolds de I'air base sur le diametre de l'orifice s'echelonne entre 50 et 40000. L'etude porte surtout sur une description unifiee des phenomenes de bullage, depuis la formation d'une bulle unique jusqu'a la formation de jets, ainsi que sur les transitions entre les diverses regions de bullage. On a conch que pour les orifices utilises c o m e dispositifs d'injection et le systeme air/eau Btudies, le nombre de Reynolds constitue la variable de contrble pour les phenomenes de bullage au-dessus des tuyeres et pour la transition entre les diverses regions de bullage.

The outer region of a turbulent boundary layer along a flat plate was photographed and analysed; in addition, limited observations of the wall area were also made. The technique involved suspending very small solid particles in water and photographing their motion with a high-speed camera moving with the flow.The single most important event observed in the outer region was fluid motion which in the convected view of the travelling camera appeared as a transverse vortex. This was a large-scale motion transported downstream almost parallel to the wall with an average velocity slightly smaller than the local mean. It appeared to be the result of an instability interaction between accelerated and decelerated fluid, and it is believed to be closely associated with the wall-region ejections. The transverse vortex was part of a deterministic sequence of events; although these events occurred randomly in space and time. The first of these events was a decelerated flow exhibiting velocities considerably smaller than the local mean. It was immediately followed by an accelerated flow. Both these events extended from near the wall to the far outer region. Their interaction resulted in the formation of one or more transverse vortices. While the transverse vortex was transported downstream, small-scale fluid elements, originating in the wall area of the decelerated flow, were ejected outwards (ejection event). After travelling some distance outwards the ejected elements interacted with the oncoming accelerated fluid in the wall region and were subsequently swept downstream (sweep event). The sequence of events closed with two large-scale motions.Estimated positive and negative contributions to the instantaneous Reynolds stress during the events were many times higher than the local mean values.

No abstract

It is my pleasure to acknowledge my teachers and friends who contributed to this work. I wish to express my special thanks and appreciation to my adviser, Dr. Robert S. Brodkey, who suggested the subject of this dissertation, enthusiastically followed its progress, and was never tired to work with his student in the lab until the early hours in the morning. My special thanks are also extended to Dr. Harry C. Hershey for his continuous advice during the course of this investigation.

A pattern recognition technique has been applied to data obtained in a turbulent channel flow. The u signal patterns are recognized using several simple criteria, but simultaneously, other signals are processed. A newly designed probe provides, in addition to simultaneous u, v, and w signals, vorticity signals, ωz and ωy, and a signal which can be interpreted as the instantaneous turbulence production, uv (∂U/∂y). The ensemble averaged results provide insight into the vorticity dynamics and turbulence production characteristics of organized structures. The instantaneous turbulent production results show that ejection-type motions are the principal turbulent energy producers and that the interesting dynamics occur during the acceleration phase of the recognized pattern. A partial model of the flow which explains the results is offered.