Interior near-field acoustical holography in flight

In this paper boundary element methods (BEM) are mated with near-field acou stical holography (NAH) in order to determine the normal velocity over a la rge area of a fuselage of a turboprop airplane from a measurement of the pr essure (hologram) on a concentric surface in the interior of the aircraft. This work represents the first time NAH has been applied in situ, in-flight . The normal fuselage velocity was successfully reconstructed at the blade passage frequency (BPF) of the propeller and its first two harmonics. This reconstructed velocity reveals structure-borne and airborne sound-transmiss ion paths from the engine to the interior space. (C) 2000 Acoustical Societ y of America. [S0001-4966(00)03310-5].