Software para modelização de turbinas

ISIMADE, Baden-Baden, 1999
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Hydro Turbine Design in a VR Environment
E. Goede 1) , A. Kaps 1), A. Ruprecht 1), U. Woessner2)
1) Institute for Fluid Mechanics and Hydraulic Machinery (IHS), University of Stuttgart
2) Computing Center (RUS), University of Stuttgart
Introduction
Usually hydraulic turbines have to be designed individually according to the local operating
conditions of power station such as discharge, head and given geometrical situations. This
requires a tailor-made design mainly for the turbine runners. The shapes of the runners are
rather complicated and therefore the understanding of the complex geometry and especially
of the spatial structures of the flow are very difficult to analyze by two-dimensional display
tools. Many different views and cuts have to be prepared and analyzed, which is quite
uneconomical and time consuming. In a virtual reality environment, however, the complex
geometry and especially the flow behavior can be controlled much faster and in more detail.
This is particularly the case for students, who are not completely familiar with turbine shapes.
Consequently a design tool based on VR-techniques is developed at IHS and RUS. The
system is used for educational purposes as well as for industrial applications.
The primary design is obtained on the basis of Euler's equation for turbomachinery. The
design parameters such as head, discharge, speed, number of blades can be changed by
sliders. Other parameters, e. g. blade angle can be manipulated by interaction in VR using
3D interaction devices. Since Euler's equation is relatively simple the geometrical shape can
be calculated online. Therefore many sets of parameters can be investigated and optimized
in a short time.
After the primary design the blade shape is fixed and can then be analyzed by numerical flow
simulation. The flow calculation, based on the Navier-Stokes equations, can be carried out
on a supercomputer in order to achieve a short response time. The calculated flow behavior
is studied in the VR-environment. Again, it is much easier to understand the complex
relations between the flow and the geometry in VR than using two-dimensional display
facilities. This is principally of great importance for people not entirely accustomed with
turbine runner flows. Consequently the VR-environment is particularly important for
educational purposes.
Visualization Software
COVISE is a software environment developed by the Computer Center (RUS) which tries to
integrate visualization and simulation tasks across heterogeneous hardware platforms in a
seamless manner. The user interface is based on the visual programming paradigm.
Distributed applications can be built by combining modules (modeled as processes) from
different application categories on different hosts to form more or less complex module
networks. At the end of such networks usually the rendering step does the final visualization.
A special feature of COVISE is that it allows several users to work in a collaborative way
providing online consulting to end users at remote sites or tele-teaching. For the visualization
COVISE supports desktop as well as VR oriented renderer modules.
Hardware equipment
For the VR based visualization two different environments are used, one at IHS and one at
RUS. In both environments the visualization runs on local SGI workstations, the flow
simulation program runs on the super-computers of HLRS (Höchstleistungsrechenzentrum
Stuttgart) either on a NEC SX-4 vector computer or on a CRAY T3E computer in parallel.
ISIMADE, Baden-Baden, 1999
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The workstations and the super-computers are connected either by a high speed network
(HIPPI, ATM) or by FDDI. The environment is schematically shown in fig. 1.
HLRS
IHS
RUS
VR
environment
VR
environment HIPPI
FDDI
CRAY T3E 512
NEC SX-4
SGI Crimson
SGI Onyx2
Fig. 1: Working environment
The currently installed hardware at IHS is
a single wall back projection system
driven by a SGI RealityEngine system,
see fig. 2. A four side back projection
system called the CUBE is installed at
RUS. The CUBE is connected to a
Silicon Graphics Onyx2 double rack
system with 14 R10000 CPUs and 4GB
of main memory. The Onyx2 has three
InfiniteReality pipes each equipped with
two raster managers. Several magnetic
tracking systems such as Polhemus
Fastrack with Stylus pen and the
Ascension Motionstar with 3D mouse are
supported for the interaction of the user
with the virtual environment.
Design System
It is a parametric design system based on Euler's equation for turbomachinery. Using this
equation the flow angles upstream as well as downstream of the runner can be calculated
that are needed to produce the runner torque necessary for the required turbine power
output. These flow angles are transformed to blade angles taking into account knowledge
based assumptions for incidence and deviation angles. In between, from leading to trailing
edge of the blade, mean lines are created and profile coordinates are added taken from
catalogue. Then, curvature and thickness distributions are optimized using CFD in order to
define the final blade shape.
Simulation software
The flow simulation is carried out using FENFLOSS, a finite element flow simulation
program, developed at IHS. It is based on the Reynolds averaged Navier-Stokes equations
Fig. 2: VR equipment at IHS
ISIMADE, Baden-Baden, 1999
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with various models of turbulence. Usually the k-ε model is used. FENFLOSS runs on
various platforms ranging from PC to vector-supercomputers and massively parallel
machines. The parallelization is obtained by a domain decomposition algorithm with
overlapping meshes. For the online simulation FENFLOSS has been integrated into COVISE
as a module.
Application
The application shown in this
paper is an axial propeller
turbine. The geometry of the
adjustable guide vanes and of
the fixed runner blades is
shown in fig. 3. The turbine is
composed for the following
main data:
• Head: 7.9 m
• Discharge: 5.6 m3/s
• Speed: 250 rpm
• No of runner blades: 6
By using the design system the
influence of the different
parameters can be easily
demonstrated. So the students
as well as the industrial
customers can get an
impression of the blade shape
very fast. As an example in fig.
4 the runner blades are shown
for the data described above as
well as for a reduced discharge
rate of 4 m3/s keeping all other parameters constant. The influence of the discharge can be
seen clearly. For the high flow rate the runner blades are steeper. By reducing the flow rate
the inlet and outlet angles of the blades have to be more flat and consequently the blade
channel is becomes narrower.
As already mentioned after the preliminary investigation of the blade shapes the flow in the
runner is calculated numerically. For this calculation a computational grid is needed. Usually
a periodical flow condition is assumed. Consequently only one channel of the runner has to
Fig. 3: Geometry of an axial propeller turbine
a) high discharge rate b) lower discharge rate
Fig. 4: Runner blades design for two different discharge rates
ISIMADE, Baden-Baden, 1999
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be considered. The grid is
obtained by a specialized grid
generator. A typical grid around
a runner blade is shown in fig.
5. A typical grid consists of
approximately 100000-200000
nodes. The flow is calculated in
a frame of reference rotating
with the runner. In this frame the
flow is assumed to be steady
state.
During the simulation the
results are sent from time to
time to COVISE and displayed
in the VR environment. The
current iteration step as well as
the final results can than be
analyzed interactively using VR
techniques. For example
particle traces or streamlines
can be started, cutting planes
can be located according to the
users requirements etc. This
allows a fast understanding of
the complete three-dimensional flow structure.
In fig. 6 the distribution of streamlines at the
hub for the shown geometry is presented. It
can be seen, that the flow angle corresponds
quite well to the blade angle. This is usually
the most critical part of the blade.
Conclusion
A tool for the design of hydro turbine runner is
under development for educational and
industrial purposes, respectively. The tool is
based on Virtual Reality technique. The
application of the tool during the lecture
courses allows the student to investigate
quickly the influence of the various parameters
(head, discharge, speed etc.) and
consequently to get a much better
understanding of the correlation between the
parameters and blade shape.
Contact: Dr.-Ing. A. Ruprecht
Institute for Fluid Mechanics and
Hydraulic Machinery
Pfaffenwaldring 10
70550 Stuttgart, Germany
Tel.: +49-711-685-3259
Fax: +49-711-685-3255
Email: ruprecht@ihs.uni-stuttgart.de
Fig. 5: Computational grid around the runner blade
Fig. 6: Calculated streamlines