Thermo-Mechanical Fatigue Optimization of Three Dimensional Stress Concentration Features in a Tangentially Bladed Rotor

byNicholas D. Aiello

Project OverviewProject broken into 3 parts:• Part 1: Baseline design 3D model

• Create 3D CAD model of slot area in NX

• Mesh model in ANSYS

• Apply boundary conditions and interface definition

• Run and post process results

• Part 2: 2D optimization routine• Create 2D CAD plate model of slot area in NX

• Determine 2D-3D stress factors for each mission point using 3D model and TMF lifing file

• Vary thickness of plane stress elements to replicate 2D-3D stress factors at each mission point

• Create iSight DOE to map effect of change of slot shape on TMF life of slots

• Review DOE map to determine optimal solution that meets design constraints

• Part 3: Result verification 3D model• Create 3D model of optimized geometry

• Repeat steps from part 1

• Compare stress concentrations predicted by 2D model to 3D results

Geometry Summary3D rotor model created• 3D model includes upper portion of disk web and full disk rim area• 3D stress concentration features are load slots, lock slots, and shield slots• Model is cut up for ease of meshing/applying BC’s in ANSYS

Mesh Summary

Model meshed using 3 types of 3D elements1. 10 node tetrahedron: for the complex

geometry of the area surrounding the 3D slots

2. 8 node brick: for axi-symmetric portions of the disk to help keep the element count down/increase run speed

3. 20 node brick: collapse to form the pyramid shaped elements that connect the other 2 element types

Blade Definition• Blade “stump” used to model correct

interface with disk• Mass point at CG represents the upper

portion of the blade• Stiff, massless spring elements

connect mass points to blade stumps

Boundary Condition SummaryMapped/cut boundaries• Nodes exported from 3D FE mesh• Exported nodes compressed onto mid-plane, file created for use in thermal mapping• Compressed mid-plane nodes not on cut boundaries deleted, additional file created for mapping displacements on model boundaries

Other boundaries/interfaces• Contact elements used for blade stub to disk interface

• Blades constrained for no circumferential motion• “Roller” constraints applied to disk sector boundaries