Simple prediction method of unstable fluid force in turbine blade row of steam turbine

Abstract

Unstable fluid force may be induced by rotor blade eccentricity in turbo machinery such as steam turbines. To develop a prediction method for unstable fluid force in turbine blade rows, we calculated the fluid force by using computational fluid dynamics (CFD) analysis, and the following conclusions were obtained. In this study, the unstable fluid force acting on the hub of the blade row is 0.8 to 1.2 times as large as that acting on the blades. Therefore, the unstable fluid force acting on the hub is not negligible. We developed a prediction method for unstable fluid force that uses blade tip gap sensitivity to the driving torque on a concentric blade row. The calculation error for the unstable fluid force was less than 11% compared with the CFD analysis. The maximum pressure location of the circumferential distribution of the perturbation pressure on hub is similar to that on tip seal. And the radial distribution of the perturbation pressure in front of the rotor blade row is uniform. The rotor surface region in front of the rotor blade row is the same as the hub. Therefore, the three dimensional flow is less influence to the unstable fluid force acting on the hub. And the prediction method by Benckert for unstable fluid force on the seal was applied to the hub. The calculation error for the unstable fluid force was less than 16% compared with the CFD analysis. The total calculation error for the unstable fluid force acting on the blade row was less than 13% compared with the CFD analysis.