Fluid/Structure Coupled Aeroelastic Computations for Transonic Flows in Turbomachinery

Abstract

The unstable, self-excited or forced vibrations of rotor blades must be avoided in designing high performance turbomachinery components because they may induce catastrophic structural failures. In evaluating the stability of such vibrations, computational approaches have been bearing an increasing role due to the surprising progress of both computer technologies and advanced algorithms. They are now at a stage where time domain fluid/structure coupled simulations of aeroelastic phenomena in turbomachinery with realistic geometries can be used in practice. The present study demonstrates the capabilities of a fluid/structure coupled computational approach which consists of an unsteady three-dimensional Navier-Stokes flow solver, TFLO, a finite element structural analysis package, MSC/NASTRAN, and the coupling interface between the two disciplines. The flow solver relies on a multiblock, cell-centered finite volume discretization and the dual time stepping time integration scheme with multigrid for convergence acceleration. Parallelization for multiple processors is also performed to achieve faster computations making use of the Message Passing Interface (MPI). As far as the interface is concerned, high accuracy is pursued with respect to load transfer, deformation tracking and synchronization. As a result, the program successfully predicts the aeroelastic responses of a high performance fan, NASA Rotor 67, over a range of operational conditions. The major contribution to the aerodynamic damping for turbomachinery blade motions is observed to be the unsteady pressure generated at the location of the shock. The results show that the

Aeromechanical Modeling of Rotating Fan Blades to Investigate High-Cycle and Low-Cycle Fatigue Interaction

“…Based on the amplitudes of the aero dynamic forcing functions and the resulting displacements, the IGV-rotor case has a higher aerodynamic damping coefficient of 0.104, compared to the IR, where it is 0.065, resulting in a differ ence of 38%. These values of CA are typical of turbomachinery blades and commonly reported, however, in the context of aeroelastic instabilities such as flutter, and also investigated by others [14,[33][34][35]. However, in this case, CA highlights the effect of an additional source of aerodynamic loading and how it can counter intuitively lower the magnitude of displacement and therefore, mean stresses.…”

“…Due to the complex flow mechanisms involved in a compressor/turbine cas cade such as wakes, potential flow disturbances, shocks, separa tion, tip region vortices, and secondary flows [10,40], aeromechanical experiments involving rotating blades are difficult to perform, especially with the objective of calculating fatigue damage. Hence, there are no such appropriate validation cases for FSI in open literature for comparison purposes, a limitation also experienced by Doi [33]. However, this emphasizes the need for useful, accessible experimental data that can be used in multidisci plinary cases like these.…”

A vibration analysis used in the methods of detecting unsteady operational modes of axial compressors

“…Основным недо-статком модели k-ω является большая погрешность при разрешении уравнений в свободном потоке [16][17][18]. Однако она наиболее пригодна для предсказания точки отрыва потока от поверхности лопатки, что является существенным при моделировании срывных вихревых зон.…”

A 3D Parameterization for Transonic Fan Blade Multidisciplinary Design

“…However, additional constraints are added from other disciplines: the maximum stress in the blade is constrained to be less or equal to the maximum stress of the original Rotor 67; and vibration frequency ranges are forbidden to avoid resonances. Following Doi & Alonso [17], Youngs modulus is taken as Ey = 1.422e+11 Pa, Poissons ratio, = 0.3, and density = 4539.5 kg/m3. For the vibration constraints, one rotational speed, E, is defined as E=267.4 Hz based on RPM at design point.…”