Nonembedded measurement method based on amplitude correction for unsteady surface pressure estimation in a high-subsonic compressor cascade

Unsteady surface pressure (USP) is a crucial physical quantity for studying blade loads and boundary layer flow. However, the unique characteristics of high-load compressor cascades, including thin walls, narrow passages, and significant geometric deflection angles, pose considerable challenges for USP measurements. The primary innovation of this study lies in proposing a nonembedded measurement method based on amplitude correction for USP measurement, which can provide frequency and amplitude information of dynamic pressure on measured surface. Unlike existing methods that rely on theoretical models for amplitude correction, the proposed method establishes amplitude correction transfer models using Gaussian process regression (GPR) based on pre-calibration data. This innovation overcomes the constraints faced by theoretical models when dealing with high-speed complex geometries, such as those found in compressor blades, which are limited by geometric and Reynolds number considerations. The principle of this method is to perform indirect measurement by leading the airflow out of the measured surface through an air tube and correcting the amplitudes through transfer models. An acoustic calibration system was developed for amplitude calibration and measurement verification. The results demonstrate that the developed method accurately provides the dynamic pressure frequencies in the range of 1-10 kHz with a tube length of <= 55 mm and from 1 to 7 kHz with the tube length of 80 mm. Verification results proof that the GPR statistical model can reasonably estimate amplitude attenuation. Ultimately, the developed method was successfully applied to unsteady pressure measurement in a high-subsonic compressor cascade and showed highly encouraging results.