Design and performance of two-dimensional diffusers for centrifugal compressors
The deceleration of flowing fluids, or diffusion as it is widely known,
is a process of primary importance, whereby some of the kinetic energy
is converted into static pressure rise. Hence, in the case of subsonic
flows, the area of a diffusing passage increases in the direction of
the flow. Most commonly used diffuser configurations are: conical,
annular, rectangular and radial. The rectangular shape is used widely
in vaned diffuser systems for centrifugal compressors.
In general, fluid motion in diffusing passages takes place against an
adverse pressure gradient, and unless great care is taken in the design
of these passages, the growth of boundary layer and its ultimate
separation may seriously upset the performance of the diffuser system.
From the point of view of the fundamental physics of fluid motion, the
study of diffusing flows is indeed very interesting. Therefore, it has
attracted the attention of many investigators, and a great deal of
literature has been published on the performance of commonly used
diffuser configurations. However, the available performance prediction
techniques are either far from being reliable, or they are limited to
specific geometry and fluid conditions.
In the case of rectangular diffusers, there are other aspects which do
not appear to have been fully investigated, for example:
(i) Interdependence of the geometrical parameters, operating
conditions and the performance of rectangular diffusers on
the basis of a suitable theoretical model.
(ii) Correlation between the principal dimensions of the
compressor and the geometry of the diffuser channels.
The aim of this research was to study these aspects. Full description
of the aims is given in Chapter 1. Chapter 2 gives a comprehensive
survey of the published literature and a statement of the justification
of the aims. Chapters 3,4 and 5 describe the theoretical development
for a parametric study, flow analysis and performance analysis
respectively. The results of the theoretical studies and the
comparisons between the predicted and experimental performance data are
discussed in Chapter 6. The conclusions and suggestions for further
work are given in Chapter 7.
The performance prediction method and the correlation between the
relevant dimensions of the compressor and the diffuser geometry are
believed to be novel. It is submitted that they should make a
significant contribution to the design methodology for centrifugal
compressors in general, and for two-dimensional diffusers in