Fig. 9: Comparison of noise contour maps in installed configurations for duct and ducted fans (see Table 1 and Fig. 4) at a fan rotational speed (N) of 6000 rpm for a wide range of fan thrust regimes.
From: Aeroacoustics and psychoacoustics characterization of a boundary layer ingesting ducted fan
Here, m = 1 corresponds to the blade passing frequency (BPF), and m = 2, 3, 4. . . the first, second, third, fourth harmonics, and so on. colorbar represents the sound pressure level (SPL).
