Investigations on the Blade Vibration of a Radial Inflow Micro Gas Turbine Wheel
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This paper demonstrates the investigations on the blade vibration of a radial inflow micro gas turbine wheel. Firstly, the dependence of Young's modulus on temperature was measured since it is a major concern in structure analysis. Secondly, turbine blades suffer many excitations during operation, such as pressure fluctuations (unsteady aerodynamic forces), torque fluctuations, etc. On the other hand, a turbine wheel has many kinds of vibration modes, typical ones being blade-hub (disk) coupled modes and blade-shaft (torsional) coupled modes. Model experiments and FEM (Finite Element Method) analysis were conducted to study the coupled vibration and to identify the modes, which are more likely to cause problems. It is demonstrated that Young's modulus depends on temperature greatly and the dependence should be considered in structure analysis. Anisotropy and scattering of the Young's modulus were not significant even at high temperature. The results of model experiments and FEM analysis show that torque fluctuations and uniform pressure fluctuations (the fluctuations acting on all the blades in the same phase) may excite resonance of blade-shaft (torsional) coupled modes. Impact excitations and propagating pressure fluctuations (the fluctuations propagating in the circumferential direction around the blades) may excite blade-hub (disk) coupled modes.
