Combined Effects of Both Axial Gap and Blade Count Ratio on the Unsteady Forces of a Steam Turbine Stage

Rotating blades of steam turbines are subjected to unsteady forces due to the presence of both wakes and potential field from the upstream stationary blades. These forces are strongly influenced by both axial gap and blade count ratio. The combined effects of these parameters are studied for 120 scenarios covering the normal design space. The calculated unsteady forces are transformed into harmonic components using a Fourier transform. Each harmonic component is correlated to both axial gap and blade count ratio to provide guidance for preliminary blade design. This study uses an in-house non-linear time marching CFD code TF3D-VIB, which adopts a Shape Correction method to manage an arbitrary blade count ratio using a single passage. Consequently it is one-order more efficient than a conventional multiple passage method.Copyright © 2012 by Alstom Technology Ltd.