Blade Forced Response Prediction for Industrial Gas Turbines: Part 2 — Verification and Application

Abstract

This is part two of a two-part paper. Part One describes the methodologies of a blade forced response prediction system. The emphasis of this part is to demonstrate the capability and computational efficiency of the system for predicting blade forced response. Part two firstly presents verification of the multistage time-linearized unsteady flow solver through comparison of predicted blade surface pressure distributions with data measured on a VKI transonic turbine stage. It concludes with presentation of the results of an analysis carried out on the last stage rotor blade of an ALSTOM three-stage transonic test compressor. In the analysis, strain gauge results together with Finite Element (FE) modal analysis identify the resonant crossings. The mode shape of the blade vibration is used in the CFD code to predict the blade aerodynamic damping. The aerodynamic damping is compared with the blade system damping obtained from the strain gauge tests. The variation is shown of aerodynamic and mechanical damping with blade mode shape. The blade unsteady modal forces induced by the upstream stators are derived from the calculated unsteady flows. The blade vibration at three resonant crossings is compared with those given by strain gauge measurements. Good comparisons and high computational efficiency demonstrate that the forced response methodologies described in Part One can be used in the blade design process to tackle blade aeromechanical issues.

On decoupled and fully-coupled methods for blade forced response prediction

“…Whilst mechanical damping prediction methods are immature, the work of Ning et al (2003b), indicates that mechanical damping of typical compressor blades without friction dampers is greatly reduced for high-order modes, where blade motion is concentrated within the aerofoil. It can therefore be deduced that the sensitivity to frequency shift is likely to be high for bladerow interaction problems, where high-order modes result in low mechanical damping.…”

Determination of Aerodynamic Damping at High Reduced Frequencies

“…W. Ning and S. Moffatt (Ning et al, 2003) have verified the forced response prediction methodology presented by S. Moffatt and L. He, through comparison of predicted blade surface pressure distributions with data measured on a VKI transonic turbine stage. Based on the verification, the last stage rotor blade of an ALSTOM three-stage transonic test compressor has been analysed.…”

“…The resulting strains have been compared with strain gauge measurements, and the errors of the prediction from measurements are 8%, 65% and 4% for mode 8, mode 9 and mode 10. (Ning et al, 2003) Mode 8 Mode 9 Mode 10…”

“…Figure 2-2 Mode shape of the last stage rotor in ALSTOM three-stage compressor (Ning et al, 2003) F. Figaschewsky and etc. (Beirow et al, 2016) (Figaschewsky et al, 2016) have introduced a simplified approach to estimate aerodynamic damping for high reduced frequency resonances at high inlet Mach number.…”

Adjoint-Based Aeroelastic Design Optimization Using a Harmonic Balance Method

“…This method enables flutter and forced response analysis with engineering accuracy by means of unsteady fluid-dynamic simulations. The method is based on the principle of energy conservation: the energy added by the flow-unsteadiness is equal to that dissipated by the vibrating blade [4,9]. It is an alternative to the modal reduction method.…”