Vibration test method of aero-engine 3D printing pre-swirl nozzle based on equivalent installation stiffness

Pre-swirl nozzle is an important cooling component that is located inside of aero-engine and exposed to complex vibration excitation, and exploring its vibration characteristics and durability is of significant importance, especially for 3D printing pre-swirl nozzle. The present study provides a novel vibration test method based on equivalent installation stiffness. Firstly, the vibration characteristics of pre-swirl nozzle in real engine assembly state is calculated by the finite element method, and the equivalent constraint fixture is designed and checked based on this. The check results indicate that the designed fixture can well restore the installation stiffness of engine and the strength of the test fixture elements is enough in the vibration test process. Then, the modal characteristics of pre-swirl nozzle are measured by modal test, based on which the accuracy of the finite element model is verified. Finally, a test program of vibration durability is established to evaluate the vibration durability of pre-swirl nozzle, in which the excitation frequency is determined by combining logarithmic frequency sweep and linear frequency sweep and the location of maximum stress is determined based on a novel method (density increasing method). Besides, the calibration of relation between vibration stress and excitation amplitude is completed. Based on the proposed test program, vibration durability test is performed. The results show that the natural frequency of pre-swirl nozzle only decreases by 0.62 % after 5×10⁷ cycles, which indicates that the specimen is always in the stage of fatigue crack initiation over the test duration.