Investigating noise radiation from jets by acoustic analogy

The aerodynamic noise radiating from an unsteady flow can be extracted by acoustic analogy from time-resolved Computational Fluid Dynamic (CFD) simulations. For this purpose, two Ffowcs Williams and Hawkings (FW-H) solvers are developed, based on an advanced time formulation (AFW-H) and on a convective formulation (CFW-H). The methods are coded in Python and embedded in Antares, a CFD post-processor of wide access and usability for the scientific community, developed by Cerfacs, France. The new FW-H solvers are tested on a hierarchy of noise sources of increasing complexity. The radiating field from elementary acoustic sources is considered first, progressing then to single-stream and dual-stream jets. The tests on monopoles, dipoles, and quadrupoles show good predictions of pressure fluctuation time-history and directivity against reference analytical results. CFD results obtained at Cerfacs by Large Eddy Simulation and at the University of Leicester by Detached Eddy Simulation provide the input to the acoustic analogy to estimate the noise radiation from jets. The jet noise predictions are compared against acoustic results obtained numerically by the elsA software (ONERA, France) and against sound measurements taken at the Von Karman Institute for Fluid Dynamics, Belgium. The tool is then used to assess dual-stream under-expanded jet noise in a configuration by Airbus SAS, at flow conditions that differ from the ones explored in previous aeroacoustic literature. Flight effects on jet noise are tested by applying the CFW-H tool to a single-stream under-expanded jet in-flight. The acoustic predictions for both static and in-flight jets are found in good agreement with reference predictions and with measurements, building confidence in using the new FW-H solvers to extract the aerodynamic noise generated by unsteady shock-containing jets.