Investigation of the Effect of Porosity in Lattice Structures on Mechanical Stability and Cylinder Flow Noise

Kurzfassung

Aerodynamic noise generated by flow around circular cylinders is a classical problem in aeroacoustics, which can be found, for example, at parts of the aircraft landing gear. Structured porous materials are a passive method to reduce this noise, which has received increasing attention especially due to the availability of additive manufacturing capabilities. In the current work, structured porous cylinder coatings made of three different types of regular lattice structures are investigated in a first step with respect to their structural integrity, which is done using detailed numerical simulations. In a second step, the noise generation of the cylinders is investigated experimentally in a small aeroacoustic wind tunnel, with the main focus being on the tonal noise caused by periodic vortex shedding. The numerical results show that the buckling load factor under bending and compression is strongly influenced by the lattice topology and porosity. For the most interesting configurations with high porosity, the Gyroid structure slightly outperforms the two other lattice topologies. The sound pressure measurements showed a noticeable tonal noise reduction for the porous coated cylinders in comparison to the solid baseline reference for all considered flow velocities. At 50 % porosity, the noise reduction exceeds 10 dB for all cases. Although the Schwarz D structure provided the largest noise reduction for most individual porosities, the overall trend indicates that porosity is the dominant design parameter. For future research, other acoustic material parameters should be included in the analysis to improve the physical understanding of the noise reduction mechanism.