An Aeroacoustic Numerical Model of the Transonic Flow Past a Sphere

Transonic flow past a sphere is investigated by Large Eddy Simulations. The Reynolds

number based on the diameter of the sphere and on the free-stream quantities is 1000, while the

free-stream Mach number is 0.9. This regime generates a weakly supersonic flow behind the

sphere, with a stationary compression wave a few diameters downstream which traverses the

developing turbulent wake. The focus of this study is the sound radiated from the wake turbulent

structures and their interaction with the stationary compression wave. This direct aeroacoustic

computation shows a spiral pressure wave radiating from the base flow precessing about the

free-stream unit vector passing through the centre of the sphere. The main acoustically active

region is the stationary compression wave-wake interaction one. The localised supersonic flow

over the sphere prevents the upstream radiation in a cone of silence type effect within a narrow

solid angle upstream of the sphere, which could be exploited for passive noise control.