Measurement and simulation results showing the influence of the used resonator insert () comparing with a closed resonator () at the evaluation point MP Inlet 1 in the inlet region. For both simulations a frequency resolution of about Δf ≈ 160 Hz have been achieved. The characteristic TL of the resonator insert is depicted in (). (a) Measurement results without resonator insert for t = 10 s. For postprocessing, the time signal was split into 2700 blocks with 30% overlap and a Hamming window function was used. (b) Lighthill's propagation results with open and closed resonator insert. For performing an FFT for the Lighthill propagation, the time signal of 20 turns was separated into 3 parts with 30% overlap, and a Hamming window function was used.