The increasing demand for improved performance in diesel and petrol engines - particularly
in the motor-sport industry - has increased the need for performance enhancing devices such
as the automotive turbocharger. The prediction of compressor performance in the early
design stage of a turbocharger is critical and helps to ensure that the range and matching of
the constituent components (impeller, diffuser and volute) is satisfactory. Although the fluid
flow inside the compressor is three-dimensional, effective analysis can be carried out using
one-dimensional prediction techniques. Many prediction techniques have been developed
over the decades and improvements to these methods have primarily been due to a greater
understanding of compressor operation. The major gain from establishing more accurate
prediction techniques is the reduction of uncertainties in both design time and production
costs as well as allowing existing designs of centrifugal compressors to be improved.
This thesis presents the work carried out to develop a PC-based I -D prediction technique
called CAPRICE, with focus aimed at developing new models for the vaneless diffuser and
volute casing. Extensive analysis of the existing models has been undertaken relating
geometric features to performance. A specially-constructed interstage test rig, designed to
extract data from the components, enabled experimental data from two compressors to be
gathered. The data collected was used to develop several new correlations; A new correlation
for the prediction of impeller work was produced and shown to be an improvement on the
Wiesner equation. Formulae for the prediction of impeller and diffuser surge were developed
which enabled a more accurate prediction of surge to be made. and diffuser and volute loss
and recovery coefficient correlations were produced, separating the diffusion system model in
CAPRICE for the first time. An equation for the prediction of the length of the log spiral
path in the diffuser was also derived. The work was validated against existing I-D and 3-D
models and shown to produce excellent comparisons and overall compressor maps have been
produced to demonstrate these developments throughout this work.
The resulting I -D performance prediction technique gives the designer better control of the
overall perfon-nance by allowing a greater level of adjustment to be made to the individual
component geometries, previously unavailable in CAPRICE.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.