Near-field pressure and wake dynamics in aerodynamic noise control of a forced rotating cylinder

This study investigates the aerodynamic noise control mechanisms of a forced rotating circular cylinder at a subcritical Reynolds number (

) using large-eddy simulation coupled with the Ffowcs Williams–Hawkings acoustic analogy, validated by wind tunnel experiments. Five representative rotation ratios,

alpha equals 0 α = 0 $\alpha =0$

,

0.5 0.5 $0.5$

,

1 1 $1$

,

2 2 $2$

and

4 4 $4$

, are analysed to relate wall-pressure fluctuations and wake organisation to the radiated noise. At

alpha equals 0.5 α = 0.5 $\alpha =0.5$

, the natural shedding tone separates into two components,

upper S t 01 almost equals 0.18 S t 01 ≈ 0.18 $St_{01}\approx 0.18$

and

upper S t 02 almost equals 0.23 S t 02 ≈ 0.23 $St_{02}\approx 0.23$

. Their three-dimensional (3-D) structures exhibit spanwise phase dislocation and reduced coherence, explaining the decrease in tonal radiation despite locally enhanced wall-pressure fluctuations. Coherent shedding partially recovers at

alpha equals 1 α = 1 $\alpha =1$

, whereas

alpha equals 2 α = 2 $\alpha =2$

gives the strongest tonal-noise reduction among the investigated cases, accompanied by weakened wake fluctuations, spanwise coherence and wall–wake correlation. At

alpha equals 4 α = 4 $\alpha =4$

, the classical Kármán mode is suppressed and localised near-wall helical structures are associated with a broadband elevation near

upper S t almost equals 0.1 S t ≈ 0.1 $St\approx 0.1$

. The results show that rotation controls noise through changes in both unsteady-loading amplitude and 3-D source organisation.