| Popis: |
Blending is a method of fan and compressor blade repair. The goal of the blending process is to remove stress concentration points such as cracks and nicks along the leading, trailing, or tip edges of the blade. The stressed areas are typically removed by grinding or cropping away the surrounding material. For integrally bladed rotor (IBR) disks, repairing a damaged blade is much more economical than replacing the entire disk. However, the change in shape of the blade will change the local aerodynamics and result in mistuning, both structurally and aerodynamically. In a worst case scenario, the change in the aerodynamic forces acting on the blades could lead to either flutter or resonant fatigue failure. This study focused on the effects of the unsteady aerodynamic loading of blended blades. To examine the phenomena in detail a commercial computational fluid dynamics (CFD) code was used to predict the loading of a first-stage, transonic turbofan subjected to varying degrees of blending. The study revealed the effects of the blend are not limited to the blended blade, as changes in steady and unsteady pressure loading was predicted on the other nonblended blades on the rotor. A maximum steady sectional loading change of 7% at 99% span on the blended blade for the maximum sized blend case was predicted. The unsteady analysis found an 18% maximum change in unsteady 1st mode sectional loading on the blade adjacent to the blended blade for the 18 engine order excitation at 90% span. Therefore, the potential for a serious aeromechanics issue exists which requires an unsteady aerodynamic analysis to be performed. It is difficult to determine the true aeromechanical effects without a coupled aerodynamics/structural analysis, but this aerodynamic loading investigation suggests larger blends could be safely used and should be analyzed. |
