The entrainment and mixing of a round buoyant turbulent jet in cross-flow
Thoman, David Charles, Jr
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https://hdl.handle.net/2142/22448
Description
Title
The entrainment and mixing of a round buoyant turbulent jet in cross-flow
Author(s)
Thoman, David Charles, Jr
Issue Date
1991
Doctoral Committee Chair(s)
Dunn, William E.
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
This thesis summaries the results of an experimental investigation of the near-field behavior and physics of the round buoyant turbulent jet in crossflow. In particular, the study centers on the physics associated with entrainment and mixing phenomena of the jet with the goal of better understanding the trends of trajectory and dilution behavior.
The experiments involved a downward discharge of cold nitrogen gas (at about $-$85$\sp\circ$C) from a cylindrical structure placed in a wind tunnel of horizontally flowing ambient air. The jet was mapped using thermocouple measurements. For the purpose of studying jet/crossflow and jet/wake interactions, fog-oil smoke was used to mark parcels of fluid in the crossflow upstream of the jet and in the wake flow downstream of the discharge structure. Time-averaged, smoke concentrations were gathered through an aspirated sampling probe in conjunction with a calibrated, optical aerosol monitor. Smoke distributions were also photographed. Experiments were performed for four different values for the crossflow-to-exit velocity ratio k, namely, k = 0.7, 1.3, 2.1, and 3.5.
The results of the experiments yield a comprehensive picture of the near-field flow patterns, flow interactions, and flow-transport physics for a buoyant jet in crossflow. Key, phenomenologically distinct zones of flow which comprise the near-exit structure of the jet are identified. The flow patterns within these zones, and thus the structure of the near-exit jet, are found to be extremely dependent on the value of the velocity ratio. Flow interactions in this region establish flow patterns which have a pronounced influence on the downstream development of the jet. A method is developed to fully document the trajectory and dilution behavior of the jet with the key parameters of influence. Trajectory and dilution are found to correlate with two parameters, namely, the velocity ratio and the density-difference ratio. Finally, unsteady, large-scale mixing motions within the near-exit flow zones are documented. Distinct modes of large-scale mixing which are responsible for the rapid and extensive dispersion observed in the jet are revealed by this study.
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