Planar nearfield acoustical holography in high-speed, subsonic flow

摘要

The objective is to develop a NAH procedure that includes the effects of the high-speed,subsonic flow of a fluid medium. Recently, the speed of a transportation has significantlyincreased, e.g., to close to the speed of sound. As a result, the NAH data measured with amicrophone array attached to an aircraft or train include significant airflow effects. Here,the convective wave equation along with the convective Euler’s equation is used to derivethe proposed NAH procedure. A mapping function between static and moving fluidmedium cases is also derived from the convective wave equation. Then, a new wave numberfilter defined by mapping the static wave number filter is proposed. For the purpose ofvalidating the proposed NAH procedure, a monopole simulation at Mach = -0.6 isconducted. The reconstructed acoustic fields obtained by applying the proposed NAHprocedure to the simulation data match well with the exact fields. Through an experimentwith two loudspeakers performed in a wind tunnel at the airflow speed of Mach = -0.12, itis also shown that the proposed NAH procedure can be used to successfully reconstruct thesound fields radiated from the two loudspeakers.