Propulsion systems, for example, jet engines and rocket motors, are the main intensive sound sources aircraft and space vehicles.
In this white paper, the authors have tried to detect these sound sources using phased array microphones. Successful examples are the comparison of the sound source maps observed behind the mixer nozzles of a turbojet engine, or at the exhaust of the launch pad model.
The CLEAN-based spatial source coherence (CLEAN-SC) method as well as non-negative least squares (NNLS) detects sound source maps with better resolution, compared to former approaches such as the delay and sum (DAS). This paper describes the application of CLEAN-SC techniques on a small turbofan engine, DGEN380.
A 9-armed foldable array was placed at the side of the engine in an open environment. For comparison, a random-geometry array for wideband holography (WBH) was included in the engine test during the test cell operations. The source maps by the CLEAN-SC agreed well with the results of existing methods of the DAS, WBH and NNLS, and provided better resolution in detecting sound sources. The extended CLEAN-SC, correlating a reference signal in the array with other array signals, suggested a potential for evaluating directional contribution of jet noise source.