Radial mode analysis of broadband noise in flow ducts using a combined axial and azimuthal sensor array

A method suited for the decomposition of broadband noise into duct modes is presented. The inverse method requires the application of only one circumferential ring in combination with an axial line array of microphones. In comparison to a reference array with multiple populated microphone rings specifically designed for a large-scale turbo-machinery test rig the new method reduces the amount of necessary measurement positions substantially. With the help of simulated measurements it is verified that - in case of fully uncorrelated modes - the method is accurate and delivers the same results as the reference method, which bases on the acquired data from the above mentioned reference array. The method delivers sound power estimates for each individual mode order. This enables a broader insight into the broadband noise generation mechanisms of turbo-machinery and, moreover, a more detailed assessment of noise reduction technologies.