Abstract:
Computational Fluid Dynamics (CFD) techniques have settled to a stage, where it is
possible to gain significant insight into fluid flow processes of turbomachinery.
However, the purpose of fluid dynamics naturally goes beyond improved understanding
to the aim of improving the performance of the engineering systems. Consequently, the
present thesis investigates the use of a automated design optimisation method using
CFD. This
presents a new design method for a important turbomachinery part, blade
profiles of centrifugal pump impellers, based on a shape optimisation algorithm in
combination with CFD. The use of
genetic algorithms in shape optimisation dose not
allow the
design engineer to use any derivative information on the evolution of the
shape, but only simple evaluation techniques. A optimisation library (GAlib), based on
a
genetic algorithm (GA), was used. GA controls the evolution of a population of
profiles towards an optimum design. The optimisation process can handle simple
objectives as well as conicting ones. The fitness value of each population element is
evaluated
using a CFD flow solver (Mac_LNS) based on nite-difference discretisation
of the
incompressible, Navier-Stokes (N-S) equations on structured polar-coordinate
meshes. A
number of design examples have been developed and the behaviour of the
genetic algorithm has been tested using different kinds of objective functions. I
addition, the algorithm was tested with a multi-objective mction. Bézier curves were
selected to
represent the impeller profile. A symmetric profile, identical profile for the
pressure side (PS) and suction side (SS), was used as a basic shape to generate the
population elements. GAlib was modified to run as a parallel algorithm using Message
Passing Interface (MPI). It is indicated that parallelisation using MPI is good technique
to overcome the time taken
by GA and CFD, and quite good optimisation convergence
criteria was obtained
by using parallelisation. The obtained results show that the genetic
algorithm is capable of achieving satisfactory designs of centrifugal impeller blade
profiles effectively and with a minimum amount of user expertise.