Finite element analysis of an outer bearing bush of a Kaplan turbine.
Miclosina, Calin-Octavian ; Campian, Constantin Viorel ; Frunzaverde, Doina 等
Abstract: The paper presents the finite element analysis of the
outer bearing bush of a Kaplan turbine. In order to obtain von Mises stress plot, the forces are applied on the links of the 3D model of the
runner blade operating mechanism, the motion is simulated, the meshing
of bush model is done and the stress calculus is performed. For modeling
and simulation, SolidWorks 2010 software was used.
Key words: Kaplan turbine, outer bearing bush, finite element
analysis, von Mises stress
1. INTRODUCTION
The main characteristic of the Kaplan turbine is the possibility to
modify the rotor blades angles in order to achieve high efficiency in
different water flow conditions.
The runner blade operating mechanism consists of a fork head driven
by a hydraulic servomotor, a connecting rod and the pin
lever--trunnion--blade subassembly. This subassembly is borne by the
rotor's body through an outer bush and an inner bush.
While functioning, failures occur due to high loads or fatigue
phenomenon.
Studies on the failure of different parts of Kaplan turbines were
made: runner blade (Frunzaverde et al., 2010), pin lever (Pittner et
al., 2010).
This paper proposes the finite element analysis of the outer
bearing bush. The loads during motion are computed and imported in a
static study, which is solved using the finite element method.
2. 3D MODEL OF RUNNER BLADE OPERATING MECHANISM
The 3D model of runner blade operating mechanism is presented in
fig. 1 (Miclosina et al., 2011).
[FIGURE 1 OMITTED]
The component parts are as follows: 1--hub; 2--bush; 3--fork head;
4--connecting rod; 5--pin lever; 6--trunnion; 7--inner bearing bush;
8--outer bearing bush; 9--blade. All parts have assigned materials. From
SolidWorks materials library, tin bearing bronze is chosen for the outer
bearing bush.
3. MOTION ANALYSIS OF RUNNER BLADE OPERATING MECHANISM
The blade angle at the beginning of motion is [phi] = 8,47
[[degrees]]. The dependence displacement of fork head vs. time is
presented in fig. 2 (Miclosina et al., 2011).
[FIGURE 2 OMITTED]
The forces that act on mechanism links are as follows: axial force
on the blade [F.sub.ax] = 1,771 x [10.sup.6] [N], tangential force on
the blade [F.sub.t] = 1,025 x [10.sup.6] [N], centrifugal force of the
pin lever--trunnion --blade subassembly [F.sub.c] = 4,070 x [10.sup.6]
[N]. These forces can be applied in points (fig. 3) or on surfaces
(Miclosina et al., 2011). The action force [F.sub.a] acts on surface S
of the fork head.
[FIGURE 3 OMITTED]
The variation of magnitude of action force [F.sub.a], computed by
SolidWorks software, is shown in fig. 4.
[FIGURE 4 OMITTED]
4. FINITE ELEMENT ANALYSIS OF THE OUTER BEARING BUSH
For the stress calculus, the loads on the outer bearing bush are
imported from motion analysis for the whole motion period.
In numerical simulation, stress values depend on mesh parameters
(Bordeasu et al., 2009), (Hursa et al., 2007).
Standard mesh with automatic transition option was used. The values
for global mesh sizes (GMS) were chosen as follows: 22, 25, 28, 31, 34
and 37 [mm]. Mesh with global size 22 [mm] applied on outer bearing bush
is presented in fig. 5.
[FIGURE 5 OMITTED]
Examples of meshing with different global sizes are presented in
fig. 6.
[FIGURE 6 OMITTED]
After the numerical solving of the study, the plot for von Mises
stress is obtained (fig. 7).
[FIGURE 7 OMITTED]
For different global mesh sizes, different maximum values for von
Mises stress were obtained, as shown in fig. 8.
[FIGURE 8 OMITTED]
5. CONCLUSIONS
Using SolidWorks Simulation module, the maximum values of von Mises
stress were computed for the outer bearing bush. These values vary
between 69,3 and 81,8 [MPa] and are lower than yield strength (110,3
MPa) for global mesh sizes between 22 and 37 [mm].
As further research, a fatigue analysis of outer bearing bush
follows.
6. ACKNOWLEDGEMENTS
The work has been co-funded by the Sectoral Operational Programme
Human Resources Development 2007-2013 of the Romanian Ministry of
Labour, Family and Social Protection through the Financial Agreement
POSDRU/89/1.5/S/62557.
7. REFERENCES
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Frunzaverde, D.; Campian, V.; Nedelcu D.; Gillich G.-R. &
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