Doctoral Dissertations

Fan-Ming Yu

Date of Award

6-1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Aerospace Engineering

Major Professor

Jain-Ming Wu

Committee Members

A. D. Vakili, Trevor Moulden, Mitsuru Kurosaka, K. C. Reddy, John Steinhoff

Abstract

Non-symmetric jets in crossflow have been studied with various jet geometries, jet orientations, jet characteristics and jet to crossflow velocity ratios. The asymmetric jets/crossflow interacting flow field contains many vortices, which vary significantly with the variation of the conditions of the jets and the crossflow. Under certain specific conditions, the shedding vortices appear periodically. Four different cross-section geometry jets were studied and compared with a circular jet with identical jet port cross-sectional area. Standard dye and laser induced fluorescent flow visualization techniques were used to identify the existence of various vortices in the flow field. A three components hot-film anemometer was used to aid in understanding of the highly three dimensional and complex flow field. Among many forms of secondary vortices produced, three major vortex systems were identified. These are main jet vortices, wake vortices and "spin-off" vortices. The shedding of "spin-off" vortices were found with jets orientation 10° ≤ β ≤ 30° and jet to crossflow velocity ratio R ≥ 2.6. The shedding vortices were nearly parallel to the jet exit axis with periodicity depending on the jet orientation and the jet to crossflow velocity ratio. A reconstruction of the asymmetric flow field based on observations and its evolution and relationships with established symmetric jet in crossflow were made. The large scale rolled-up vortex structure which was found at low jet to crossflow velocity ratio (R = 1) is very similar to the hair-pin vortex structure. This observation provides a potential research tool on the study of the structure of turbulent boundary layer. Unsteady jets created by pulsation of the jet flow at low pulsation frequencies give the increase of the depth of penetration. However, the introducing of swirl into jets by passive method reduces the depth of penetration.

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