m 1 "Azimuthal mode number"
f0 6000[Hz] "Frequency"
U0 40[m/s] "Background flow velocity"
M0 0.12 "Mach number"
c0 U0/M0 "Speed of sound"
rho0 1.25[kg/m^3] "Density"
a 0.085[m] "Duct radius"
L 1[m] "Duct length"
R0 2[m] "Exterior field radius"