Unsteady Simulations of a Fan/Outlet-Guide-Vane System: Tone–Noise Computation

摘要

Tone noise from a rotor-stator system representing a turbofan is studied based on high-fidelity unsteady simulations. The baseline configuration of the NASA source-diagnostic-test geometry with the entire hard-wall nacelle is solved by using the unsteady Reynolds-averaged Navier-Stokes equations and the improved delayed detached-eddy simulation at approach and takeoff conditions. Following a paper by Shur etal. (Unsteady Simulations of a Fan/Outlet-Guide-Vane System: Aerodynamics and Turbulence, AIAA Journal, 2018), which focused on the simulation methodology for the turbulence treatment and the aerodynamics, this paper investigates noise-generation/propagation phenomena of the first and second blade-passing-frequency tones: The analyses include mode decomposition of the tone power levels, their comparison with the NASA source diagnostic test data, nonlinear propagation of rotor-locked tones in the inlet, and the unsteady response of the stator against the rotor viscous wakes. With a duct-mode-matching method, the improved delayed detached-eddy simulation can predict tone levels within 6dB and usually less, except for the rotor-locked tones. Although both simulations capture nonlinear decay in the inlet, identical blade simulations are unable to redistribute the energy into multiple pure tones at the takeoff speed. In the viscous-wake/outlet-guide-vane interaction, unsteady stator responses computed by both simulations seem not to be in accordance with classical models; moreover, the unsteady Reynolds-averaged Navier-Stokes simulation can predict only cut-on tone levels due to the lack of turbulence contents.