Introduction of a Novel Parameter Model to Analyze the Geometric Variation of Airfoil Edges of Ex-In-Service Compressor Airfoils

Abstract The leading and trailing edge shapes of high pressure compressor (HPC) airfoils have a high impact on their aerodynamic performance. Typically, the shape of these airfoil edges are designed symmetrically as half circles or half ellipses. Due to manufacturing scatter and operational effects, the edges of real HPC airfoils deviate from the design intent. Especially the change in shape of the airfoil edges due to erosion can lead to a reduction of the aerodynamic efficiency and operability range. This paper introduces a novel and intuitive parametrization approach to describe the occurring airfoil edge shapes. The introduced parametric model has been applied to a set of postservice airfoils with a variety of airfoil edge shapes. For this purpose, just above 1000 of used HPC airfoils from different engines with different operational conditions and runtimes were digitized by means of a structured light 3D scanner. The high precision of the scanning system enables accurate capturing of the sensitive airfoil edge shapes. Subsequently, the extracted parameters were used for a statistical evaluation of the leading edge (LE) shape geometry. It turned out that the LEs of the investigated post-service compressor airfoils exhibit a thinner LE shape characteristics compared to the design intent LE shape. Furthermore, in nearly all cases, more material is missing on the suction sided LE of the investigated airfoils. This result is rather contrary compared to the findings of relevant literature, where the LE pressure side is missing more material due to erosion. Nevertheless, the generated results suggest that the developed method is suitable for a sufficient qualitative and quantitative description of HPC LE shapes. In future work, the introduced parametric model can be used as the basis of a prospective evaluation of the correlation between the geometric variation of airfoil edges and manufacturing scatter as well as engine operational condition.