Modal deconvolution method is used to characterize the main acoustic modes propagating in duct from non-intrusive measurements. In the framework of the ASPIRE-CS2 project, ONERA's modal deconvolution method ARMADA is applied to numerical data from a generic UHBR engine at the take-off sideline condition. The numerical simulation is provided by NLR to quantify the tonal internal acoustic field by the application of CFD approach for the configuration with clean fan channel. The complex geometry of the nacelle implies a variable Mach number through the fan duct, which is unfortunately not precisely known. As a first step, azimuthal Fourier transform is applied to determine the dominant azimuthal modes content. In the bypass duct (downstream direction), they are shown to be quite constant, whereas, upstream from the fan, they sharply vary in the vicinity of the inlet. Therefore, our deconvolution method is only applied on the bypass duct, using data obtained at BPF2 on the wall as it would be for flush mounted microphones. The modal basis is restricted to azimuthal mode orders from -1 to 11, which is relevant to explain the main content of the total sound pressure. Considering a constant flow rate with two hypotheses of Mach number (0.4 and 0.5), and under the correlated mode assumption, the results explain more than 74% of the data and dominant modes are found to be perfectly correlated. Modes propagating in the upstream direction point out possible reflections at the end of the nacelle. Finally, the acoustic pressure field is reconstructed from the estimated modes, and compared to the initial numerical data. Using only data obtained on the wall, ONERA's deconvolution method succeeds in providing a good representation of the acoustic field in the bypass duct.
展开▼
