Establishment of an open 3D steam turbine flutter test case

Sammanfattning: An open three-dimensional (3D) flutter test case for steam turbines is presented. Unlike previous research on turbine flutter, the geometry is an open resource and is from a test case originally presented by Durham University. The geometry of the test case includes the stator, rotor and diffuser, which is representative of the aerodynamic characteristics of modern steam turbine blading. The average inlet flow conditions are total pressure 27 kPa and total temperature 340 K which are typical for the last stage. The average static pressure at the exit of the diffuser is 8800 Pa. It also provides the typical flow conditions for the last stage steam turbine.The aim of current study is to define a 3D test case for open realistic steam turbine blades flutter analysis. Commercial numerical tool ANSYS CFX was used to solve Reynolds-averaged Navier-Stokes (RANS) equations for viscous flow and Laminar equations for inviscid flow for steady and unsteady state. The defined mode shape for the test case was the first flap bending mode fixed at the hub. Multi-row steady state simulations with mixing plane were performed for different length of rotor exit. Reflecting waves was found to influence both steady and unsteady simulation at the mixing plane and rotor outlet. Only the rotor was considered for the flutter analysis. The plots of normalised aerodynamic damping and local work coefficient for different Inter Blade Phase Angle (IBPA) were calculated. It showed that -90 degrees IBPA was least stable. Unsteady aerodynamic work was done mainly on the tip region of rotor blade. Initial results of tip clearance flow were only studied in the steady state.This thesis work is partly included in paper written for European Turbomachinery Conference (ETC). It is verified by comparing the results obtained from CFX and LUFT (Linearized Unsteady Flow solver for Turbomachinery) solvers.