Page 10 - Fluid Mechanics and Thermodynamics of Turbomachinery

Preface to the Fourth Edition

It is now twenty years since the third edition of this book was published and in
that period many advances have been made to the art and science of turboma-
chinery design. Knowledge of the flow processes within turbomachines has increased
dramatically resulting in the appearance of new and innovative designs. Some of
the long-standing, apparently intractable, problems such as surge and rotating stall
have begun to yield to new methods of control. New types of flow machine have
made their appearance (e.g. the Wells turbine and the axi-fuge compressor) and
some changes have been made to established design procedures. Much attention
is now being given to blade and flow passage design using computational fluid
dynamics (CFD) and this must eventually bring forth further design and flow effi-
ciency improvements. However, the fundamentals do not change and this book is
still concerned with the basics of the subject as well as looking at new ideas.
The book was originally perceived as a text for students taking an Honours degree
in engineering which included turbomachines as well as assisting those undertaking
more advanced postgraduate courses in the subject. The book was written for engi-
neers rather than mathematicians. Much stress is laid on physical concepts rather
than mathematics and the use of specialised mathematical techniques is mostly kept
to a minimum. The book should continue to be of use to engineers in industry
and technological establishments, especially as brief reviews are included on many
important aspects of turbomachinery giving pointers to more advanced sources of
information. For those looking towards the wider reaches of the subject area some
interesting reading is contained in the bibliography. It might be of interest to know
that the third edition was published in four languages.
A fairly large number of additions and extensions have been included in the
book from the new material mentioned as well as “tidying up” various sections
no longer to my liking. Additions include some details of a new method of fan
blade design, the determination of the design point efficiency of a turbine stage,
sections on centrifugal stresses in turbine blades and blade cooling, control of flow
instabilities in axial-flow compressors, design of the Wells turbine, consideration of
rothalpy conservation in impellers (and rotors), defining and calculating the optimum
efficiency of inward flow turbines and comparison with the nominal design. A
number of extensions of existing topics have been included such as updating and
extending the treatment and application of diffuser research, effect of prerotation
of the flow in centrifugal compressors and the use of backward swept vanes on
their performance, also changes in the design philosophy concerning the blading of
axial-flow compressors. The original chapter on radial flow turbines has been split
into two chapters; one dealing with radial gas turbines with some new extensions
and the other on hydraulic turbines. In a world striving for a ‘greener’ future it was
felt that there would now be more than just a little interest in hydraulic turbines. It
is a subject that is usually included in many mechanical engineering courses. This
chapter includes a few new ideas which could be of some interest.