Date of Award

5-2016

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Ebenezer Gnanamanickam

First Committee Member

Dr. J. Gordon Leishman

Second Committee Member

Dr. Reda Mankbadi

Abstract

Jets are seen commonly in nature and engineering and can be broadly classified into steady and unsteady jets. The study of unsteady jets has received little attention when compared to its steady counterpart. A type of unsteady jet is the turbulent puff which is a momentum driven jet in which fluid is ejected from a jet orifice intermittently. Common examples of turbulent puff like jets are coughs and volcanoes. The studies on momentum driven unsteady jets have primarily focused on single ejection events (single puffs) where an instantaneous supply of momentum drives the source fluid downstream of a nozzle. This work focuses on dual puffs in which two volumes of fluid (dual puffs), separated by a time ∆p are ejected from a jet orifice into ambient. An experimental framework to study such dual puffs with varying separation and ejected volume was built. The dual puffs studied were compared with both steady jets and single puffs. The mean velocity of these flow fields were measured using hot-wire anemometry. Complementary flow visualizations were also carried out. Dual puffs with ∆p = 0.3 s, 0.5 s, 0.7 s ans 1.79 s were considered. It was determined that for short time separations ∆pVj/d = 430, the dual puffs persisted for longer distances when compared to a single puff or dual puffs with larger time separation (∆pVj/d = 1540). Here Vj is the maximum jet exit velocity and the d the diameter of the jet orifice. However, at large time separation (∆pVj/d = 1540) the dual puffs expanded considerably more rapidly than dual puffs with smaller separation or single puffs. This indicates that the dual puff studied can be classified into two categories based on the time separation between the puffs. These observations are of an integral nature and a more detailed analysis of the flow field using advanced techniques as particle image velocimetry (PIV) are recommended to establish the precise flow physics leading to this behavior.

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