Unsteady CFD simulation of transonic axial Compressor stages with distorted inflow

Abstract

The research unit “Simulation of Wing and Nacelle Stall” (FOR1066) funded by the DFG, Airbus, and Rolls Royce Deutschland, investigates new numerical methods to simulate wings in high lift configurations, nacelles and highly loaded compressors coupled in one single simulation environment, and coupled meteorological simulation of wind gusts. Subgroup B of FOR1066 deals with aircraft nacelle stall and its interaction with the jet engine. In this paper latest results of project B2 are presented, putting the focus on numerical investigations and detailed analyses of interaction phenomena between distorted inflow and a transonic axial compressor stage. The challenge in simulating such configurations was approached by coupling two specialized CFD codes: TAU for the external flow around the nacelle and TRACE for the internal flow through the compressor. A coupling library has been implemented and applied to several test and validation cases. Details of the numerical complexity of the setup and initialization of coupled simulations and the challenges to approach complex configurations are outlined in the paper. The research unit uses two different test cases to study the impact of flow distortions on transonic compressors in detail, namely the DLR-R030 test case and the axial compressor rig of TU Darmstadt in its rotor1 configuration. The Darmstadt rig has been modified for the purposes of the research unit to investigate the influence of inflow distortions on compressor performance and provided highly detailed and well validated simulation results. Different flow distortion generating devices were designed and analyzed, which led to a deeper understanding of the unsteady behavior of the flow in axial compressors. One major result is the finding, that at the distortion boundaries static pressure and inflow velocity become decoupled during their propagation through the compressor stage. This provides an explanation for the unsteady flow features observed in both experiment and simulation.