Numerical Investigations of Turbulent Flow in Water Turbines
Doktorsavhandling, 2002
This thesis investigates turbulent flow in water turbines, focusing on
the flow in the vicinity of reaction water turbine runners such as the
Kaplan runner and the Francis runner. The method of investigation
is principally numerical although some experimental observations and
measurements made in the present work and elsewhere are included.
A major part of the present work was to implement an efficient and
general CFD (Computational Fluid Dynamics) code that could resolve
the complicated geometry of a water turbine. A parallel multiblock
finite volume CFD code, CALC-PMB (Parallel MultiBlock), was developed.
The main features of the code are the use of conformal block
structured boundary fitted coordinates, a pressure correction scheme
(SIMPLEC), Cartesian velocity components as the principal unknowns
and a collocated grid arrangement together with Rhie and Chow interpolation.
The turbulence is modeled using a low-Reynolds k-omega turbulence
model. The parallel multiblock algorithm employs two ghost cell
planes at the block interfaces. The message passing at the interfaces
is done using either PVM (Parallel Virtual Machine) or MPI (Message
Passing Interface).
Three water turbine runners are used for the investigations, two Kaplan
runners and one Francis runner. One of the Kaplan runners was
used during the development of the CFD code. This runner could not
be used to validate the CFD code but the work on this runner still gave
valuable insights on CFD in water turbines. The other Kaplan runner
is a model of the runners installed in the H¨olleforsen power plant in
Indals¨alven in Sweden. The computational results of the H¨olleforsen
wicket gate and runner flow are validated against the thorough experimental
investigations from the Turbine 99 workshops and additional
LDV (Laser Doppler Velocimetry) measurements made in the present
work. The Francis runner model investigated here was used as a test
case at a GAMM workshop in 1989. The present computational results of the GAMM Francis runner are validated against measurements at
both the best efficiency operating condition and four off-design operating
conditions. Several important flow features are visualized to make
comparisons with experimental observations and to better understand
the flow in water turbine runners. The validations against both detailed
measurements and experimental observations show that the flow
is captured qualitatively correctly.
A method for numerical verification of the computational results has
been derived and applied to the computational results of the present
work. The method is based on the conservation of a sub-set of the angular
momentum equations that is particularly important to swirling
flow in water turbines. The method is based on the fact that the discretized
angular momentum equations are not necessarily conserved
when the discretized linear momentum equations are solved. The method
shows that the first-order hybrid discretization scheme cannot be
used and that the second-order Van Leer discretization scheme needs
improvement to give quantitatively correct results in these kinds of
applications.
Multiblock
Parallel
Visualization
Validation
Verification
Turbine
CFD
Francis
Numerical
Kaplan
10.00 HA2, Hörsalsvägen, Chalmers
Opponent: Professor V.C. Patel, Iowa Institute of Hydraulic Research, the university of Iowa, USA