BPF = blade (or vane) passing frequency

c

= chord

\[k_{1},\ k_{2}\]

= excited diametrical modes

f

= frequency (Hz);

N = vane or blade count;
N = rotational speed (rpm);
p = static pressure (Pa);
m = mass flow rate (kg/s);
η = aerodynamic efficiency;
Ω = angular velocity (rad/s);
ω = mode angular velocity (rad/s);
ρ = density (kg/m3);
µ = dynamic viscosity (kg.m-1.s-1);
θ = angular position (rad);