Effects of ambient crossflows and density stratification on the characteristic behavior of round turbulent buoyant jets
Creators: name: Wright, Steven Jay
Publisher: name: California Institute of Technology
Year: 1977

description: This investigation considers a round, turbulent buoyant jet in an ambient crossflow that is either of uniform density or with a linear density stratification.  The primary emphasis is the development of a fundamental understanding of the jet properties that are of interest in engineering design problems.  These include jet trajectories, characteristic dilutions, and in the case of a stratified crossflow, the maximum and equilibrium heights of rise.

Most previous studies of similar buoyant jet flows have used the integral method to solve for the jet characteristics.  This approach requires an assumed relation for the rate of entrainment of ambient fluid by the jet, and also depends upon experimental evidence to estimate values for the coefficients in the assumed relation.  Most previous experimental studies have been directed toward evaluating entrainment coefficients and have not considered a systematic investigation of the effects of the various jet and ambient flow parameters.

A major objective of this investigation is to provide a basis for the interpretation and extension of the results from previous theoretical and experimental investigations.  A systematic dimensional analysis is performed to define the basic problem and to provide approximate solutions without using the integral equations.  The analysis indicates the types of experiments necessary to adequately describe general buoyant jet behavior and also provides a framework for the presentation of experimental data.

The approximate solutions for the jet characteristics were derived from the dimensional analysis by considering asymptotic descriptions of a general buoyant jet as different effects become predominant in determining the flow behavior.  The limiting cases considered are for the jet behavior controlled by either its initial momentum or by its buoyancy for situations where the ambient velocity either is relatively large or approaches zero.  Combinations of these four asymptotic descriptions can be used to approximately describe a general buoyant jet.  Several different types of flow behavior can be expected, depending upon the relative magnitudes of various characteristic length scales associated with these buoyant jet flows.  These different types of flow can be compared to the theoretical solutions proposed by other researchers, providing a basis for better understanding previous research.

Experiments were performed to confirm the asymptotic relations developed in the analysis, to evaluate the coefficients in the relations, and to determine the limits of their applicability.  The experimental configuration was a salt water jet discharged downward into a tank of less dense fluid with either uniform density or linear density stratification.  The Boussinesq approximation implies that these results will be comparable to a buoyant jet rising in a less dense ambient fluid.  The crossflow was simulated by towing the jet source along the water surface in the tank.

Jet trajectories and dilutions were measured for the experiments with an unstratified crossflow.  For the experiments performed with the tank stratified, maximum and equilibrium heights of rise, a few trajectories, and jet dilutions were measured.  The results of these various experimental measurements are presented in a unified manner to facilitate the application to design problems.

The experimental evidence indicated that the coefficients in the asymptotic relations were somewhat dependent upon the initial jet volume flux, an observation that has not been previously noted by other researchers.  This variation can be expected from the dimensional analysis and is shown to be significant in some instances.
description: © 1977 W. M. Keck Laboratory of Hydraulics and Water Resources. California Institute of Technology. 

Supported by; National Science Foundation Grant Numbers GK-35774X, ENG 75-02985 and ENG 75-02985 A01. 

I hardly know where to begin. To acknowledge everyone who helped me out at critical points would be difficult, if not impossible. This is especially true since I may not realize how such the help of others has contributed to my reaching this point. Let me try anyway. Even though I have thanked him many times, I would like to take this opportunity to acknowledge the efforts of Dr. John Roberson on my behalf.
It was at his suggestion that I first decided to apply to Caltech, so I can truly say that without him, I would not be here today. I would also like to recognize the efforts of Dr. Norman Brooks, especially in helping to turn this manuscript into something readable. I just hope that I can do as much for someone else sometime in the future.
It was also Dr. Brooks' suggestion that I pursue this area of research and he provided the impetus for my getting started in the right direction. At the time that many of the ideas presented in this manuscript were only halfway thought out, several valuable discussions with Dr. E. John
List helped me to understand the problem. These discussions, class lectures, and an unpublished manuscript were helpful in providing the framework on which my understanding of the research was developed. Without Dr. List's guidance, It is safe to say that this research would be incomplete. I also want to thank Dr. Fredric Raichlen for h1a help and interest at various stages of my research. In particular, he helped me to get started developing the light probe, and this help is greatly appreciated.
There are of course, many others whose general comments and advice helped me out along the way. I would especially like to recognize Greg Gartrell, Phil Roberts, and Bob Koh for the contributions that they made to this research. The National Science Foundation supported this research under Grant Numbers CK-35774X, ENG-75-02985 and ENG 75-02985 AOL This financial support is greatly appreciated along with the assistance California Institute of Technology both in the form of research facilities and financial support. The laboratory experiments could not have been performed without the help of several individual. Elton Daly and Joe
Fontana bad to turn my half-completed sketches into final products, and their ability to do so never ceased to amaze me. In addition, Elton taught me enough along the way so that it will be easier for me to develop laboratory experiments in the future. Several others helped out during the course of the experiments including Linda Figueroa, Bob
Shultz, Dave Byrum, and Rich Eastvedt. It make me realize just how dependent on others I was just to list those names. Then there was the preparation of the manuscript. I would like to specially thank Joan Mathew for her patience and ability in deciphering the material that I gave to her and putting it in a presentable form. The same goes for Dave Byrum with respect to the drafting of the figures.
Adelaide Massengale also assisted in the preparation of the manuscript. Finally, I would like to acknowledge the efforts of two special people who helped me so much, especially in getting through the difficult times. Vito Vanoni was a constant source of encouragement to me and
there were times that I really needed encouragement. Some of his enthusiasm for his profession and life in general rubbed off along the way and I im grateful for the interactions that I had with Vito. I am also grateful for the support and patience of my wife, Dayle. There were difficult times and times when I have been very busy, and I am afraid that I have neglected her in those situations. Now it's her turn to do the same to me as she begins to work on her degree. So I expect similar acknowledgment a few years from now. This report was submitted on May 17, 1977 as a thesis for the degree of Doctor of Philosophy in Civil Engineering at the California Institute of Technology.