Comparison of different acceleration techniques and methods for periodic boundary treatment in unsteady turbine stage flow simulations

This paper studies different acceleration techniques for unsteady flow calc ulations. The results are compared with a nonaccelerated, fully explicit so lution in terms of time-averaged pressure distributions, the unsteady press ure and entropy in the frequency domain. and the skin friction factor. The numerical method solves the unsteady three-dimensional Navier-Stokes equati ons via an explicit time-stepping procedure. The flow in the first stage of a modern industrial gas turbine is chosen as a test case. After a descript ion of the numerical method used for the simulation, the test case is intro duced. The purpose of the comparison of the different numerical algorithms for explicit schemes is to facilitate the decision as to which acceleration technique should be used for calculations with regard to accuracy and comp utational time. The convergence acceleration methods under consideration ar e explicit time-stepping with implicit residual averaging, explicit time-co nsistent multigrid, and implicit dual time stepping. The investigation and comparison of the different acceleration techniques apply to all explicit u nsteady flow solvers, This paper also examines the influence of the stage b lade count ratio on the flowfield. For this purpose. a simulation with a st age pitch ratio of unity. is compared with a calculation using the real rat io of 78:80, which requires a more sophisticated method for periodic bounda ry condition treatment. This paper should help to decide whether it is cruc ial from the turbine designer's point of view to model the real pitch ratio in unsteady flow simulations in turbine stages. [S0889-504X(00)00702-9].