Type

Directivity

Mechanism

Leading edge interaction noise

Dipole

Atm. turbulence impinging on rotor trailing edge

Trailing edge noise

Cardioid

Boundary layer turbulence passing over rotor trailing edge

Blade tower interaction

Dipole

Rotor blade passing through flow perturbed by tower

Tip noise

Cardioid

Turbulence interacting with the rotor tip

Airfoil tonal noise

Cardioid

Vortex shedding