Experimental Investigation of Flow and Noise Control by Porous Coated Tandem Cylinder Configurations

The aerodynamic noise generated by aircraft landing gear components is often studied using a so-called tandem cylinder configuration, consisting of two circular cylinders arranged in a streamwise row and separated by a certain distance. The subject of the present study is the experimental investigation of the effect of porous coatings on the noise generated by such a tandem cylinder configuration. This was done by performing acoustic and flow measurements in a small aeroacoustic wind tunnel at Reynolds numbers (based on cylinder diameter) between 30,000 and 130,000. It is found that the porous coatings lead to a decrease of both the tonal noise and the broadband noise and to a notable shift of the resulting tonal noise peak toward lower frequencies. The noise reduction is mainly caused by the stabilizing effect of the coating of the upstream cylinder on the wake flow and the absorption of turbulence by the coating of the downstream cylinder. The observed shift of the frequency is most likely due to the mean velocity reduction in the wake of the porous coated upstream cylinder and the interaction of the turbulent flow with the porous coating of the downstream cylinder.