Computational Fluid Dynamics Simulation for a Parametric Preswirl Rotor-Stator System

Abstract

The secondary air system (SAS) has a significant impact on the performance and lifetime of the aero engine. More than 20 % of the core flow is passed through the SAS, so its optimization is one essential step to increase the efficiency of the entire engine. The system is a network of a great number of elements with different complexity levels. While for some elements, like pipes or orifices, general characteristics suffice to represent the physical behavior, for other elements or even sub-domains these models are very sensitive and may get inaccurate with changes in design or operating conditions. This justifies the use of 3D simulations for discrete domains that can give a more detailed picture of the flow field. The results of these simulations can be made available for use in the 1D network model. Vice versa the network model can provide boundary conditions for the 3D simulations, like mass flow and temperature at the domain boundaries. An interesting domain to investigate with a 3D CFD simulation is the stator-rotor cavity of the first high-pressure turbine stage. On the one hand cooling air is provided for the rotor disk and blades and on the other hand inflow of hot gas into the inner wheel space is prevented. The cavity is fed by a preswirled flow through nozzles and additionally by a cross flow through the leakage between the stator and rotor walls from a lower radius. This leads to a formation of a complex vortex structure in the cavity, which requires detailed 3D CFD simulations to show all flow phenomenons accurately. The geometrical design of those cavities differs considerably between different engines. A major research interest lies in varying the considered geometry and in studying the effects of individually changed geometric parameters. This allows to gain experience, which parameters are the essential factors for optimization of the SAS. For this purpose, a parametric geometrical model that enables the independent variation of single parameters is presented. The steady-state RANS simulation is performed with the CFD solver TRACE, which is being developed by DLR. The numerical setup is discussed and an overview of the flow behavior in the cavity is given. An evaluation of the numerical methods is part of the research.