Sound Power Estimation of Rotor-Stator Interaction Modes Based on Vane Surface Pressure Measurements

Kurzfassung

Sound power is an essential quantity for evaluating the sound emission by turbomachinery. This paper presents a novel method for estimating the sound power generated by rotor-stator interaction. It is based on measurements taken with unsteady pressure sensors at several positions distributed over the vane surface. By integrating the measured source distribution and utilizing source models based on the in-duct Green's function, the method can separate the contributions of the cut-on and cut-off radial modes. The method enables analyses on test rigs where the installation of microphone arrays at the inlet or outlet for accurate radial mode detection is not feasible. It further provides insight into the sound generation in individual stages of multi-stage rigs. The approach was tested on DLR's fan test rig CRAFT, which was equipped with 16 sensors on two opposite vanes. The estimated mode sound power was compared with reference data from radial mode analyses in the inlet and outlet. To investigate deviations in the estimated sound power, post-test simulations were performed using the Harmonic Balance method to analyze the spatial distribution of the unsteady vane pressure. The results revealed that the accuracy of the estimation is highly dependent on the ability of the sensor distribution to capture the dipole characteristic at the leading edge. Specifically, at low fan rotational speeds, where cut-off modes dominate the leading-edge pressure, the employed sparse sensor arrangement proves insufficient. The analysis concludes that at least six radial sensor positions near the leading edge are required to effectively separate cut-on and cut-off modes at 2BPF. Furthermore, a smaller, uniform chordwise sensor spacing is recommended to better resolve phase variations. This study provides critical guidelines for optimizing sensor placement to improve the accuracy of source characterization in fan stages.