Turbine Fan Disk Setback Offset for Stress Dissociation
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Solution Overview
Problem
Turbine engine fan disks experience cumulative tangential and bending stresses, leading to risks of breakage or degradation, particularly in the zone of the setback where these stresses converge.
Innovation Solution
The fan disk design offsets the setback axially upstream, concentrating tangential stresses downstream and bending stresses upstream, with a frustoconical portion to reinforce high-stress zones and lighten low-stress areas, eliminating stress convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the setback is positioned at the upstream radial face of the rim, then the disk structure is compact, but tangential and bending stresses become cumulative leading to breakage risk
Solution Approach 1:
The setback is offset axially upstream from the upstream radial face by 1-3mm, moving the stress concentration zone from the critical upstream face area to a different axial position where it does not coincide with peak tangential stresses. This spatial relocation in the axial dimension prevents stress cumulation.
Solution Approach 2:
A frustoconical portion is added to the inside surface of the disk, creating a localized geometric feature that redistributes stresses. The frustoconical shape with angle 1°-10° provides gradual stress transition and prevents sharp stress concentrations at the setback zone.
2Stability of the object's composition
If balance weights or balance hub are added to the disk, then rotational balance is improved, but access to central nut and space utilization are reduced
Solution Approach 1:
The blade roots themselves serve as counterweights through their mass distribution in the slots. The dovetail-shaped blade roots are positioned and dimensioned to provide the necessary balance moments without requiring additional balance weights or balance hubs, thus maintaining clear access to the central nut.
3Strength
If the disk structure is reinforced to handle cumulative stresses, then strength is improved, but weight increases
Solution Approach 1:
Instead of uniformly reinforcing the entire disk, the frustoconical portion is localized to specific zones where stress distribution needs improvement. This targeted reinforcement provides necessary strength while minimizing additional weight compared to full disk reinforcement.
Solution Approach 2:
The frustoconical portion introduces a curved, gradual transition surface that distributes stresses more evenly compared to sharp edges or flat surfaces. This geometric curvature reduces stress concentrations without requiring excessive material addition.
Data Source
AI summary
A turbine engine fan disk including a cylindrical rim including in its outer periphery substantially axial slots for mounting blade roots and opening out to a radially upstream face of the rim is provided. A shroud extends from the rim and connects with a rotary drive shaft. A cylindrical lip extends upstream from the upstream face of the rim. The inside surface of the disk having a cylindrical portion extended upstream by a portion of greater diameter that forms a setback that is axially offset upstream relative to the upstream radial face of the rim.