City Research Online

Abstract

The performance of conical diffusers with axial and swirling flew has been considered. As a necessary starting point the various criteria used for defining performance have been reviewed and have been extended to swirling flew cases. A new 'AREA-PLOT' method, which unifies presentation of performance information, for plane and conical diffusers has been proposed.

An added attraction of this method is that it displays all three geometric variables of the diffusers.
As swirl modifies the boundary layer it was necessary to have same knowledge of the growth of the boundary layer in the axial flew situation. This was achieved by extending the 'ROSS-FRASER' model as a closed form solution requiring only the initial boundary conditions. The predictions compare very well with published experimental results.

The swirling flow case has been considered both mathematically and experimentally, the latter being studied through flew visualisation and measurement. An extensive survey of available literature, on theoretical and experimental work, has been presented with particular emphasis on areas not covered by previous surveys.

The mathematical analysis was aimed at identifying the dominant parameters. The solution indicates the preferred coordinate system and the possibility of further extension. It has been shown that it is possible to represent the tangential velocity distribution in the diffuser by a family of exponential curves. Further analysis indicated that the divergence of the solid-body rotation core was parallel to the wall of the diffuser.

Few visualisation studies have identified breakdown and non-breakdown areas in turbulent swirling pipe flow. The development of the various modes of breakdown have been recorded. Detailed flew measurement in the 10° diffuser indicates that swirl has a definite effect on eliminating separation tendencies. It was found that swirl modifies the wall static pressure drop in the inlet pipe immediately upstream of the diffuser.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses School of Science & Technology School of Science & Technology > Engineering

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