Research on Sound Propagation in Sound-Absorbent Ducts With Superimposed Air Streams. Volume I

Application of Ray Acoustics to the Propagation of Sound in Ducts Containing Sheared Flows

“…The refraction law for the wave normal in its most general form has derived in the literature see Hayes (17) and can be written as (8) In the present study the speed of sound is assumed constant across the duct, and the flow velocity V is a function of z only. With these conditions, the general equation 8 reduces…”

Interaction Between Air Flow and Airborne Sound in a Duct

“…From (7) and (10) Ax/2 (13) where Xmnin0ýO is the position of the first pressure minimum nearest to the orifice and…”

“…13) the flow boundary layer of a flat plate was shown to be controlled by acoustical means at the stagnation point of the plate. Another point of interest is the possibility of acoustic boundary layer control not so much in the stagnation point but during the development of the boundary layer along the plate itself.…”

“…13) in sound absorbing ducts with superimposed air flow have not answered the question of how the shape of the acoustic wave fronts are influenced by the gradient of the flow velocity. Another question in this connection is the existence of a stable wave front in ducts with lateral dimensions comparable with the wavelength.…”

“…In another Report (ref. 13, Vol III), a theory was given for the computation of the sound attenuation in absorbing ducts with superimposed air flow. The wall impedance of the absorbers in the presence of the flow entered into this theory.…”