Experimental Investigation on Forced Response of Mistuned Axial Compressor Rotors

Purpose: This paper investigates experimentally the aerodynamic performance and forced response characteristics of two rotors (baseline and optimized design) under the influence of frequency mistuning effects. Method: The optimized rotor blade was obtained by a multidisciplinary optimization framework, in which the aerodynamic performance and vibration characteristics were improved numerically. From steady-state aerodynamic measurements, the total pressure ratios at different operating conditions of the baseline and optimized blade were measured and validated. The optimized blade demonstrated a 0.5% improvement in total pressure ratio and a consistent shift of the performance curve towards higher mass flow rates. Ten modified cylinders were uniformly installed circumferentially in front of the rotor to serve as the excitation source, so the forced response of both baseline and optimized blade during the acceleration process was observed and measured by using the blade tip-timing technique. Results: Blade tip-timing data analysis revealed that the rotor blades exhibited relatively strong responses at engine order (EO) 10 and 12, which was caused by the coupling effect of the upstream cylinder and downstream outlet stator. A detailed analysis and evaluation were required because they were found to be close to the design speed. Compared with the baseline blade, the maximum vibration amplitude decreased by 7.3% for EO = 10, and the amplitude magnification factor reduced from 1.56 to 1.47, approximately 5.7%. Similarly, for EO = 12, the maximum amplitude and amplitude magnification factor of optimized blade also decreased by 18% and 3.5% respectively. Furthermore, an improved fundamental mistuning model (FMM) was employed to predict the vibration amplitudes of all blades. The average predicted vibration amplitudes exhibited good agreement with the measured values in the deterministic analysis. Especially for the case of EO = 12, the relative error of the averaged amplitude was less than 1%. However, accurately predicting the maximum amplitude remains challenging due to the complex structural and aerodynamic coupling. The maximum relative error exceeded 16%. Conclusion: Even so, both experimental and numerical results indicated that the amplitude magnification factor of optimized blade was smaller than that of the baseline.