The fluid mechanics of swirling flow within annular regions

Date of Completion

January 1995

Keywords

Engineering, Mechanical

Degree

Ph.D.

Abstract

Swirling flows through annular passages occur in many engineering applications. One area of particular interest concerns the swirling flow of fuel through injection nozzles for liquid fuel combustion systems. Within this device, very high levels of swirl are induced in the fuel to obtain a uniform dispersion of fine fuel droplets at the inlet to the combustion chamber. In view of the importance of this and other similar flows, the present work investigated the fluid mechanics of highly swirling flows within annular passages.^ The experimental investigation documented the establishment and evolution of the internal flow field within the annular region. These measurements were done using laser Doppler velocimetry. Associated numerical results for fluid dynamics models of the flow were obtained using the TEACH code. Primary concerns were initiation of swirl via discrete jets, their mixing to produce a circumferentially uniform field, and the effects of level of swirl upon the overall flow pattern. Additional areas of interest concern flow path geometric effects on the evolution of this flow including effects of annulus concentricity.^ Experimental measurements indicate very high levels of swirl (near tangential) generated within these geometries even though flow was admitted over a range of initial swirl angles down to 20 degrees from axial. The high levels of swirl induce axial flow distribution heavily weighted toward the outer radius with regions of axial flow reversal seen near the inner. This flow reversal is characteristic of vortex breakdown in this confined flow. Additionally, the uniformity of the velocity field was seen to be very sensitive to annulus concentricity.^ Calculated flow fields, although limited by axisymmetry, did qualitatively show the same trends seen in measured data with high flow levels calculated near the outer radius and axial flow reversal occurring near the inner. Overall levels of calculated swirl however, were lower than measured. ^

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