Comparisons between circular and square coaxial jet flows

Document Type

Conference Proceeding

Publication Date

1-1-2000

Abstract

Visualization and flow spectra measurement results are presented for unforced flows emanating from circular coaxial nozzles, and square coaxial nozzles with parallel sides. The experiments were conducted at a co-flow-jet Reynolds number of 19,000 and at an inner-to-outer jet velocity ratio of 0.3. The visualizations and local measurements have indicated enhancement in mixing when square nozzles are used compared to the circular ones. The presence of large-scale periodic structures is evident for both nozzle configurations in the midfield of the inner mixing region, which has wake characteristics. The outer mixing region, which is highly turbulent and displays a -5/3 inertial range from its onset at the nozzle exit, shows no signs of an "indigenous" organized structure. The spectra obtained in the square nozzle mixing regions both on the center plane and the diagonal planes are mutually consistent indicating the same broad frequency peaks. The spectra from the turbulent shear layers of the middle mixing region near field indicate the presence of a short-lived shear layer preferred mode at a much higher frequency than the one associated with the subsequent development of the wake downstream. The spectral characteristics of the circular and square nozzle combinations are qualitatively similar. However, the discrete frequency peaks associated with the wake of the inner mixing region are much broader in the case of the square nozzles. More importantly, the dominant frequency at the end of the midfield within the inner mixing region, is lower in the case of the square nozzles compared to that of the circular ones. This can be explained by differences caused by the enhanced mixing observed for the square nozzles in the wake that forms upon the disappearance of the inner potential core. © 2000 The American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Publication Source (Journal or Book title)

38th Aerospace Sciences Meeting and Exhibit

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