Aeroacoustic whistling mechanisms in perforated pen caps

This paper investigates the acoustic behavior of a perforated pen cap, which acts as a compact self-sustained whistling system. Through experimental measurements and numerical simulations, we analyze the aeroacoustic interaction between jet flow dynamics and resonator geometry to identify conditions under which sound generation and amplification occur. The study highlights key aeroacoustic mechanisms and demonstrates pedagogical value, while suggesting practical implications for the design of flow-induced sound devices.