Estimation of Logarithmic Decrement of Rotor Blades under Centrifugal Force(Estimation Method by Using Specific Damping).

This paper presents an estimating method of logarithmic decrement for the actually shaped blade of compressor or turbine by using vibration test data of simply shaped blade by rotating test apparatus. In this method, logarithmic decrement of actual blade can be obtained as ratio of damping energy which is calculated using specific damping corresponding to vibration and centrifugal stress, to twice of vibration energy which is calculated by vibration stress. The comparison between the estimated logarithmic decrement value and the measured one of the compressor blade of a gas turbine is discussed. As a result, it is clarified that present method is available to estimate the logarithmic decrement of actual blades.