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Title:An Experimental Study of Single and Multiple Turbulent Buoyant Jets in Crossflow
Author(s):Leylek, Jim A.
Department / Program:Aeronautical and Astronautical Engineering
Discipline:Aeronautical and Astronautical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(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.
Issue Date:1984
Description:270 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
Other Identifier(s):(UMI)AAI8422115
Date Available in IDEALS:2014-12-15
Date Deposited:1984

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