Numerical Study of the Unsteady Blade Row Interaction in a Three-Stage Low Pressure Turbine

The focus of this paper is on the one hand the quantitative optimization of the unsteady numerical simulations compared to experiments, and on the other hand to gain a better insight into the underlying mechanisms when an upstream wake of a stator interacts with the flow-field of the next stator. This was achieved by optimizing the numerical turbulence parameters used in the turbulence and transition models. Using steady calculations an optimal initial solution for the unsteady calculation was found. Also, the computational mesh was refined. For the numerical computations a time accurate Reynolds averaged Navier-Stokes solver is applied. Turbulence is modeled using the Spalart-Allmaras one equation turbulence model. The integration of the governing equations in time is performed by an implicit time integration for the steady calculations, and by an implicit dual time stepping scheme for the unsteady calculations. At the inlet and outlet reflecting or non-reflecting boundary conditions are used. The quasi 3D calculations are conducted on a stream surface around midspan allowing a varying stream tube thickness. The results show that by adjusting the turbulence parameters in the turbulence and transition models, a better qualitative and quantitative agreement between experiments and numerical results can be achieved. Steady and unsteady quantities are shown, e.g. the surface pressure distribution and the wall shear stress. The unsteady simulations of two different azimuthal positions of the first and third stator reveal different evolutions of the boundary layers of the second and third stators due to the influence of the wake of the upstream stators. These differences are better captured through the above mentioned improvements, i.e. reduction of sheared cells in the computational mesh and optimization of turbulence and transition parameters in the allowable range of the models.Copyright © 2003 by ASME