Estimation of Dynamic Stresses in Last Stage Steam Turbine Blades Under Reverse Flow Conditions

Last stage steam turbine blades are known to suffer high alternating stresses under low volumetric flows of steam. The low volumetric flows result in a reverse flow condition and the resulting response is unstable vibration that occurs predominantly at fundamental mode of the blade. Besides the high alternating stresses, the last stage blades are also subjected to severe centrifugal load stress that when combined with the alternating stress is responsible for fatigue failures. This paper presents a method of assessing the steady and dynamic stresses under low volumetric flows.