Roughness Investigations on In-Service High-Pressure Compressor Blades—Part I: An Automated Process for High-Fidelity Roughness Measurements

The two-part publication deals with roughness investigations on in-service high-pressure compressor (HPC) blades, both in terms of measurements and simulations. In this article (Part I), an automated process for performing detailed surface roughness measurements of the blades has been developed. Specifically, a highly accurate Alicona sensor (20x lens; capable of capturing roughness values down to $0.1μm$⁠) was combined with a pick-and-place robotic arm, and the system was trained to conduct roughness measurements on all the different rotor blades of a 10-stage HPC. First, the Alicona measuring device is validated against a NanoFocus device of similar accuracy. Then, a detailed measurement of the roughness on the suction and pressure side of Rotor 2 is demonstrated, using a 100-point grid. This process is further accelerated by using a reduced number of measuring points. The location of those points has been determined by numerical optimization that aims at minimizing the error between a radial basis function (RBF)-based approximation model and the detailed measured roughness distribution. Finally, a summary of the roughness measurements through the entire HPC is given (rotors only; before and after cleaning of the blades at an ultrasonic bath) and the article ends with a discussion of the results.