Influence of fluid-structure interaction modelling on the stress and fatigue life evaluation of a gas turbine blade

Abstract

A computational method of fluid-structure coupling is implemented to predict the fatigue response of a high-pressure turbine blade. Two coupling levels, herein referred to as a “fully coupled” and “decoupled” methods are implemented to investigate the influence of multi-physics interaction on the 3 D stress state and fatigue response of a turbine blade. In the fully-coupled approach, the solutions of the fluid-flow and the solid-domain finite element problem are obtained concurrently, while in the decoupled approach, the independently computed aerodynamic forces are unilaterally transferred as boundary conditions in the subsequent finite element solution. In both cases, a three-dimensional unsteady stator-rotor aerodynamic configuration is modelled to depict a forced-vibration loading of high-cycle failure mode. Also analyzed is the low-cycle phenomenon which arises due to the mean stresses of the rotational load of the rotating turbine wheel. The coupling between the fluid and solid domains (fully-coupled approach) provides a form of damping which reduces the amplitude of fluctuation of the stress history, as opposed to the decoupled case with a resultant higher amplitude stress fluctuation. While the stress amplitude is higher in the decoupled case, the fatigue life-limiting condition is found to be significantly influenced by the higher mean stresses in the fully-coupled method. The differences between the two approaches are further explained considering three key fatigue parameters; mean stress, multiaxiality stress state and the stress ratio factors. The study shows that the influence of the coupling between the fluid and structures domain is an important factor in estimating the fatigue stress history.

Influence of Blade-Flow Interactions on Flow Behaviours and Blade Loading of an Automotive Mixed-Flow Turbine

“…( 9) and ( 10) to conserve the energy balance at the interface. For maximum equivalent stress, similar trend was reported by Ubulom [30] and Moffat and He [31] who studied comparison of FSI for coupled and non-coupled cases for gas turbine. These studies were referred since there was no study found for MFT.…”

The turbulence models review for aerodynamic, thermal and structural problems in jet engine turbines.

“…При этом, если исследуются вибрационные явления, то колебания лопатки будут оказывать влияние на поток газа, что и имеется в виду при двустороннем FSI, который среди прочего дает более точные результаты в задачах на исследование усталостной прочности и долговечности [50]. Для турбин использование FSI в расчетах тоже является обычной практикой.…”

Simulation and experimental investigation on vibration of a radial turbine wheel using a two-way FSI approach

“…For the simulation analysis method for studying the forced vibration of turbine blades, the biggest difference between the unidirectional and two-way FSI simulation analysis methods is that the unidirectional fluid-solid coupling simulation analysis method simplifies the influence of aerodynamic damping on the FEA model, while the two-way FSI simulation analysis method takes this factor into account. 17,18 The most common and simplest way to prevent resonance excitation or determine the resonance speed is to make predictions by drawing a Campbell diagram; that is, resonance occurs when the working frequency and the natural frequency are consistent. Although this method is very useful for simple dynamic structural design, it has serious limitations when studying complex components such as turbocharger turbine blades.…”