Kolodyazhnaya “A coupled Fluid-Structure Analysis for 3D Flutter

ABSTRACT 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. In this formulation of a coupled problem, 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 annulus) 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 a 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. -internal energy of mass unit, χ -ratio of the fluid specific heats, Ω -finite volume. INTRODUCTION Modern turbomachines operate under very complex regimes where a mixture of subsonic, transonic and supersonic regions coexist. With recent advances in internal compressible flow modelling and increased computational power, it is now possible to undertake both steady and unsteady flow analysis of very complex turbomachinery geometry. The trend for improved gas turbine engine design with higher aerodynamic blade loading and smaller physical size attracts much attention to the aeroelastic behaviour of blades not only in compressors, but also in turbines. Flow-induced blades oscillations of the turbine and compressor can lead to fatigue failures of a construction and so they represent an important problem of reliability, safety, and operating cost. Aeroelasticity phenomena are characterised by the interaction of fluid and structural domains, most prediction methods tend to treat the two domains separately, and they usually assume some critical interblade phase angle for which the flutter analysis is carried out for a single passage. The undeniable importance of spatial and nonlinear effects for practical turbomachinery configurations has led to the development of three -dimensional methods. Since the early 1980's a number of time accurate Euler and Navier -Stokes procedures have been developed to predict blade row unsteady flows in which unsteadiness is caused by aerodynamic disturbances at the inflow or outflow boundaries, relative motions between the blade rows, or blade vibrations. The traditional approach in flutter calculations of bladed disks is based on frequency domain analysi