Aerodynamic noise increases in proportional to the high power of velocity. So, the noise is a sever problem for high-speed transport vehicles or flow-related machinery. For example, intense tonal sound radiates from a cavity flow and flow around a cascade of flat plates, where the feedback loop due to fluid-acoustic interactions occurs. To clarify the mechanism of acoustic radiation and establish the methodologies for noise reduction, we are performing wind tunnel experiments and aeroacoustic direct numerical simulation with an in-house code (AADNS).