A Combined Experimental-Computational Technique for the VibrationCharacteristics of the Externals in Gas Turbine Engines

摘要

Determining vibrational characteristics of external components in gas turbine engines is an important process to ensure structural integrity of both the components and the supportingstructuresduringengine development testing. These external components typically are tubes, generators, fuel pumps, and fuel control units. The external components vary in size, and their mounting configurations, thus making their vibratory response unique for each application. This paper presents a combined experimental and computational technique designed to identify and predict the component vibratory response. This procedure helps to identify the high response components early in the development program where appropriate actions can be taken. The first step in this technique is to determine the resonance frequencies of the accessories either by modal ring testing or by Finite Element Analysis (FEA). However, the best way is to have the components as installed on the engine, where proper boundary conditions are included in the test setup. Once the resonance frequencies are identified, all components with potentially damaging resonance conditions are instrumented with strain gages or accelerometers. Engine test was then carried out with unbalanced rotors to measure the maximum possible dynamic strains or vibration levels of the critical external components. The vibration responses of these various components are then fed into the corresponding 3-D FE models to calculate the dynamic stresses. These 3-D FE models are also used to determine the mean stresses due to maneuver loads. The combined engine induced dynamic and flight induced mean stresses are then used to predict the High Cycle Fatigue (HCF) strength of the components and the supporting structures.