2012-07-23

Fluid-Structure Interactions in Turbines

Prof. Romuald Rzadkowski, PhD, Polish Academy of Sciences, Gdańsk

20 Sep 2012, 17:00; Location: S4|10-1

A three-dimensional nonlinear time-marching method and numerical analysis for aeroelastic behaviour of oscillating blade row has been presented. The approach is based on the solution of the coupled fluid-structure problem in which the aerodynamic and structural  equations are integrated simultaneously in time. Thus providing the correct formulation of a coupled problem, as the interblade phase angle at which a stability (or instability) would occur, is a part of the solution.The ideal gas flow through multiple interblade passage (with periodicity on the whole annuls) is described  by the unsteady Euler equations in the form of conservative laws, which are integrated by use of the  explicit monotonous second order accurate Godunov-Kolgan volume scheme and moving hybrid H-H (or H-O) grid. The structure analysis uses the modal approach and 3D finite element model of the blade. The blade motion is assumed to be a linear combination of modes shapes with the modal coefficients depending on time. The  influence of the natural frequencies on the aerodynamic coefficient and aeroelastic coupled oscillations for the Fourth Standard Configuration is shown. The stability (instability) areas for the modes are obtained. It has been shown that interaction between modes plays an important  role in the aeroelastic blade response. This interaction has essentially nonlinear character and leads to blade limit cycle oscillations.

Numerical simulations of 3D viscous flutter were performed and compared with the available experimental results. The calculations were carried out for bending oscillations of the cascade known as the Eleventh Standard Configuration. The developed numerical algorithm solves the 3D Reynolds-averaged Navier-Stokes equation together with the Baldwin-Lomax turbulence model, using the explicit monotonous second-order accurate Godunov-Kolgan finite-volume scheme and moving hybrid H-O structured grid. Comparison of the calculated and the experimental results for the Eleventh Standard Configurations has shown sufficient quantitative and qualitative agreement for local performances (unsteady pressure amplitude and phase distribution) at off-design conditions. Benchmark solutions are provided for various values of the inter-blade phase angle.

Numerical calculations of the 3D transonic flow of an ideal gas through turbomachinery blade rows moving relatively one to another with taking into account the blades oscillations is presented. The algorithm proposed allows to calculate turbine stages with an arbitrary pitch ratio of stator and rotor blades, taking into account the blade oscillations by action of unsteady loads caused both outer flow nonuniformity and blades motion. There has been performed the calculation for the stage of the turbine with rotor blades of 0.765 m. The numerical results for unsteady aerodynamic forces due to stator-rotor interaction are compared with results obtained with taking into account the blades oscillations.

Category: CE Seminar

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