Numerical study of flow and acoustic modal characteristics of fan tonal source based on DMD

As is well known, aircraft noise has become an important issue in the civil aviation transportation industry, and the importance of fan noise will increase with the emergence of the next generation of ultra-high bypass ratio (UHBR) engines. It is necessary to reduce fan noise. Many technologies have become mature and perfect, but some noise reduction technologies have not been further applied due to engine strength or structural reasons. The overall benefits of existing fan noise reduction technologies are decreasing, and research on fan noise reduction technologies has entered a bottleneck. The intake/exhaust duct of fans provides a new way to reduce the noise of fans. However, the studies are all based on the Tylar&Sofrin acoustic mode theory, but its assumption is not reasonable to the sound source area due to rotational interference and complex turbulent flow fields. The data-driven flow field modal separation methods (DMD) that have emerged in recent years provide new tools for duct acoustic modal decomposition. A single-stage axial flow fan is taken as the research object, and the CFD and TPP method was used to numerically simulate the axial fan tonal noise in this paper. The solution of URANS was adopted here to obtain the rotor-stator interaction tonal noise sources. Using DMD methods, numerically analyze the flow acoustic modal characteristics of a fan duct at the sound source area and far field. The DMD method can decompose acoustic modes at different frequencies in the fan inlet area. By comparing the DMD mode energy of the cross-section between the rotator and stator interaction and the inlet section, the same order harmonic frequency between the rotator and stator interaction is significantly higher than that of the inlet area, and the difference gradually increases with the increase of harmonic frequency order.