INTERACTION BETWEEN AIR FLOW AND AIRBORNE SOUND IN A DUCT. VOLUME I. PROPAGATION OF SHOCK FRONTS AND NONLINEARITY OF POROUS ABSORBERS.
Final rept. Feb 64-Jan 65,
GOETTINGEN UNIV (WEST GERMANY) PHYSIKALISCHES INSTITUT
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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
- Fluid Mechanics