Accession Number : AD0669085

Title :   INTERACTION BETWEEN AIR FLOW AND AIRBORNE SOUND IN A DUCT. VOLUME I. PROPAGATION OF SHOCK FRONTS AND NONLINEARITY OF POROUS ABSORBERS.

Descriptive Note : Final rept. Feb 64-Jan 65,

Corporate Author : GOETTINGEN UNIV (WEST GERMANY) PHYSIKALISCHES INSTITUT

Personal Author(s) : Mertens,P. A.

Report Date : NOV 1967

Pagination or Media Count : 34

Abstract : The sound propagation in moving air with locally varying flow velocity is investigated by means of shock waves from a spark discharge. To accomplish this, the wave fronts were photographed with a schlieren optics in a flow duct with a large flow boundary layer thickness. Results of these experiments agree with the theories of geometrical acoustics and can be incorporated into the design of ducts having air flow and airborne sound. Also investigated were properties of porous absorbers in the presence of an air flow. Results show a penetration of the absorber by the air flow yields a change of the flow resistance compared with still air. The acoustic flow resistance and the differential static flow resistance are experimentally found to have the same value. Moreover, it is proved that turbulent motions along the surface of the absorber do not affect the flow resistance appreciably. (Author)

Descriptors :   (*AERODYNAMIC NOISE, *DUCTS), (*SOUND TRANSMISSION, POROUS MATERIALS), ACOUSTIC INSULATION, ABSORPTION, INTERACTIONS, AIRBORNE, PROPAGATION, SHOCK WAVES, NONLINEAR SYSTEMS, GAS FLOW, SOUND, BOUNDARY LAYER, ACOUSTIC IMPEDANCE, WEST GERMANY

Subject Categories : Aerodynamics
      Acoustics
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE