Prediction of Unsteady Force for Steam Turbine Buckets

An effect of nozzle-bucket axial gap length on the unsteady force acting on steam turbine buckets was studied by using a new method to predict the unsteady force which is induced by a potential field interaction and a wake interaction between nozzles and buckets. The new method can separate the unsteady force into two components due to the potential field and the wake interactions by calculating the inviscid and the viscous flow solution, and the effect of nozzle-bucket axial gap length is obtained. A simple relationship between the nozzle-bucket axial gap length and the unsteady force was found to give easy and reliable prediction of the unsteady force.