Thermo-Mechanical Fatigue Optimization of Three Dimensional Stress Concentration Features in a
Tangentially Bladed Rotor
Abstract:
Thermo-mechanical fatigue has become a significant concern with respect to rotor life in turbine
engines as maximum metal temperatures have increased in newer designs. Stress concentration
features, such as those present in a tangentially bladed rotor, tend to be the primary areas of concern
for this type of fatigue. This paper will explore the optimization of a set of three dimensional stress
concentration features, using both two and three dimensional finite element analysis, subject to the
realistic design constraints of a functional tangentially bladed rotor in a turbine engine.
Introduction/Background:
Resources Required:
Software:
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MatLab: Initial optimization routine using governing equations
Finite element solver (ANSYS): Solve finite element model optimization steps, verify solutions
CAD software (NX Unigraphics): Create geometric input for finite element model
Process automation software (iSight): Automate iterations in optimization routine
MS Office: Writing thesis paper, creating summaries
Other:
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Library (Cole/PW library): Get further information (papers, textbooks, etc.) relating to project
Advisor (Prof. Gutierrez-Miravete): Project guidance, expert opinion, and verification of
formulation/results
Expected Outcomes:
The outcome of this thesis project is to create a method of optimizing a load, lock, and shielding
slot configuration for a tangentially bladed rotor, such as that of a turbine engine. The optimization
routine will explore the design space of the problem, given a set of inputs, and choose an optimal
solution based on output parameters/targets. Inputs to the optimization routine will be of the shape of
the whole rotor, a thermal profile for the rotor, the mission that the part will be subjected to, a
parameterized shape of each slot, and the shape of the blade root that must fit in the loading slot; and
output parameters will be the maximum compressive and tensile stresses in each feature, the
corresponding temperatures that occur with these stresses, and a calculated TMF life using these
outputs. The optimal solution will maximize TMF life in these features by balancing their lives with one
another while still allowing for installation of a tangential blade into the rotor.
The first step in this project will be to evaluate a baseline design for the rotor. The analysis will
be conducted on a three dimensional sector model of a bladed disk and will be run for a complete
mission. This will be used to calculate initial lives for the two load (foward and aft), lock, and shield slots
used in the pattern. The second step will be to create an accurate two dimensional representation of the
load/lock/shield slot pattern that will mimic the results of the three dimensional model. This two
dimensional model will be a plate model with cutouts representing the slots, thickness to match the
effect the outside of the part has on the stress concentration (Kt), and properly scaled loading to (at
least qualitatively) mimic the stress field the slots are subjected at different points in the mission. This
two dimensional model will also provide a means for ensuring that a blade will fit into the load slot of
the rotor, acting as a limitation on the size of the forward and aft slots. Once the two dimensional model
is accurately predicting the results obtained in the three dimensional baseline model, the third step will
be to create an optimization routine to analyze the effect of changing the parameters on TMF life. Using
the two dimensional, as opposed to the three dimensional, model for the optimization routine will allow
for a much larger number of cases to be run in a given amount of time. The optimization routine will
also have certain constraints built into its evaluations based on the physical constraints of the problem;
like having lock slots, which must accept locks that sit between blades, not overlap where a blade sits; or
providing a maximum amount that a blade’s bearing surface may hang into the loading slot in its
installed position. The final step in this process will be to take the optimized geometry, as predicted by
the two dimensional model, and create another three dimensional model to evaluate the accuracy of
the results obtained. If the final three dimensional model does not sufficiently match the two
dimensional results, the two dimensional model will be reworked such that the results accurately
represent both three dimensional models analyzed and the process will be repeated.
Upon completion of the optimization routine detailed above, an analysis of the effectiveness of
the approximations will be completed. The discussion will walk through the results of a couple of slot
configurations in both two and three dimensional approximations, and comment on the differences in
results and analysis time, possibly suggesting a better method for optimization in the design space.
Milestone/Deadline List:
1st Draft of Project Proposal: Sept 23, 2011
Final Draft of Project Proposal: Sept 30, 2011
1st Draft of Project Report: Oct 20, 2011
2nd Draft of Project Report: Nov 11, 2011
Final Draft of Project Report: Dec 2, 2011
Final Project Report: Dec 16, 2011
References: