Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly-Loaded Transonic Turbine Stage

Abstract

The viability of a scaling technique in prediction of forced response of the stator and rotor blades in a turbine stage has been examined. Accordingly the so called parameter, generalized force, is defined which describes the excitation of a modeshape due to the unsteady flow forces at a certain frequency. The capability of this method to accurately predict the generalized forces serves as the viability criterion. The scaling technique modifies the geometry to obtain an integer stator, rotor blade count ratio in an annulus section while maintaining steady aerodynamic similarity. A non-scaled configuration is set up to serve as the reference case. Further configurations with different scaling ratios are also generated for accuracy comparison. Unsteady forces are calculated through 3D Navier-Stokes simulations by VolSol, which is based on an explicit, time-marching. A general purpose finite element model of blades is also provided to enable modal analysis with the harmonic forces. The generalized forces of stator and rotor blades revealed high sensitivity towards modification of stator blades while acceptable accuracy was obtained by moderate modifications of the rotor blades for first harmonic forces. Moreover the influence of variable blade’s structural characteristics proved to be remarkable.