905461.fig.0011a
(a) Nonporous reference airfoil,
905461.fig.0011b
(b) Porous airfoil made of Needlona felt, ,200 Pa 
905461.fig.0011c
(c) Porous airfoil made of Recemat, ,200 Pa 
905461.fig.0011d
(d) Porous airfoil made of M-Pore Al 45 ppi, = 1,000 Pa 
Figure 11: Three-dimensional third-octave band sound maps, PPS 14/4 turbulence grid,  m/s ( = 548,000), CLEAN-SC beamforming algorithm, center frequency 2 kHz. (Note that all sound maps are scaled to the same maximum level measured for the reference airfoil.).