HPC Based Analyses of Turbomachinery Flow Problems#
Matthias Meinke (RWTH Aachan Univ.)
Abstract#
The flow field in a 1.5-stage axial flow turbine including the wheel space is predicted by large-eddy simulation (LES). The Navier-Stokes equations are solved using a parallel finite-volume solver based on a Cartesian mesh with immersed boundaries. The strict conservation of mass, momentum, and energy is ensured by an efficient cut-cell/level-set ansatz, where a separate level-set solver describes the motion of the rotor. Both solvers use individual subsets of a shared Cartesian mesh, which they can adapt independently. The focus of the flow field analysis is on the region inside the rotor-stator cavity, i.e., between the stator and rotor disks for various cooling gas mass flow rates. First, the time averaged flow field obtained from the simulations is discussed, followed by a detailed investigation of the unsteady flow field. The results for the cooling effectiveness are compared to experimental data and show good agreement. It is shown that for a lower cooling gas mass flux several of the wheel space’s acoustic waves are excited. This is not observed for the higher cooling gas mass flux. The excited waves lead to stable, i.e., bounded fluctuations inside the wheel space and result in a significantly higher hot gas ingestion. Those unsteady modes, which generate the dominant hot gas ingress are determined by computing the frequency dependent ingress. Finally, a mode decompositioning of the three dimensional flow field is performed to visualize the three-dimensional unsteady phenomena responsible for the hot gas ingress.