An Experimental Study of Single and Multiple Turbulent Buoyant Jets in Crossflow
Leylek, Jim A.
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https://hdl.handle.net/2142/70624
Description
Title
An Experimental Study of Single and Multiple Turbulent Buoyant Jets in Crossflow
Author(s)
Leylek, Jim A.
Issue Date
1984
Department of Study
Aeronautical and Astronautical Engineering
Discipline
Aeronautical and Astronautical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Fluid and Plasma
Abstract
The phenomenon of turbulent, buoyant jets in crossflow is a fundamental fluid mechanics problem with many application areas, including jets discharged from natural and mechanical draft cooling towers. Buoyant jets have been studied for many years, and as a result there exists a large body of literature on this and other related topics. An extensive review of this literature showed that there was a need for an improved laboratory simulation technique and quantitative data on both single and multiple buoyant jets.
A new buoyant jet simulation technique is developed which uses a vertically downward discharge of cold nitrogen gas into a wind tunnel with discharge temperature of the jet ranging between -30(DEGREES)C and -150(DEGREES)C. This technique is capable of simulating the puff-like nature of prototype cooling tower plumes as evidenced by flow visualization which is inherent in this method. A large body of data are reported for both single and multiple jets covering a wide range of parameters. Single jet data are obtained for discharge densimetric Frounde number F varying between 0.2 and 2.4 and crossflow-to-exit velocity ratio k varying between 0.2 and 11.7. The multiple jet data are reported for three angles of orientation (theta) with F values varying between 1.1 and 2.7 and k between 0.5 and 3.
The single jet results show that trajectory is very sensitive to k. The discharge densimetric Froude number also affects the trajectory but to a lesser extent. Temperature decay, on the other hand, is more sensitive to F than it is to k. An increase in k has the effect of lowering the trajectory of the jet. The isotherm downwind extension, which is a measure of effective jet mixing, increases with k for k less than the critical value k(,*). For k > k(,*) this trend reverses, indicating a more enhanced jet mixing. Physically, k(,*) indicates onset of jet/wake interaction. In highly buoyant jets, jet/wake interaction is prolonged until very high k.
The multiple jets show that the inline configuration ((theta) = 0 degrees) results in considerably high trajectory compared with the oblique and crossflow cases for all F and k combinations encountered in the experiments. The oblique case trajectories are consistently higher than crossflow trajectories for k k(,*) the oblique case exhibits by far the lowest trajectories. Two mechanisms are identified for having a key role in the behavior of multiple buoyant jets, these are: (a) jet shielding and (b) jet/wake interaction.
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