Sound measurements within and in the radiated field of an annular duct with flow

Recent theory on sound propagation for flow ducts initiated a research program (sponsored by NASA-Langley, Contract NAS1-10472) which has the objective of comparing detailed acoustical measurements with the analytical predictions for sound propagation in a duct with sheared flow. The effects considered experimentally are mean flow, shear, wall impedance, and source distribution on sound propagation within and radiation from finite length annular ducts. Results reported here are confined to acoustic distribution in hard annular ducts with and without mean flow and radiated field patterns for the same conditions. These acoustic distributions are shown for single and multi-mode excitation. The flow duct facility is also described.