Numerical Investigation of Generation and Propagation Effects of Axisymmetric Rotor-Stator Interaction Modes

Kurzfassung

The experimental determination of mode sound power emitted by turbomachinery components within rig environments is essential in the acoustic design process of aero engines. However, due to the axial spacing required for conventional acoustic instrumentation concepts like Radial Mode Analysis, an application in the axial rotor-stator gaps of modern aero engine components is not possible. Part of an ongoing collaborative effort of DLR and MTU Aero Engines is to investigate experimentally and numerically the applicability and possible limitations of estimating excited acoustic modes based on unsteady vane surface pressure, to allow for experimental instrumentation concepts in close proximity to the stages' acoustic sources. An experimental study was performed on DLR's fan test rig CRAFT supported by numerical simulations of the experimental setup, which are validated using data measured on the vane surface as well as in the inlet and outlet. The axisymmetric rotor-stator interaction (RSI) modes at 2BPF is of particular interest, because the measured mode sound powers in the inlet show significant scattering into higher radial mode orders depending on the operating conditions. The mode scattering can occur at the fan or at points of cut-off-/cut-on-transition along the spinner. The analysis of the numerical results addresses the mode generation close to the acoustic sources on the stator vanes and propagation effects at the spinner.