Experimental Investigation of the Tonal Noise Generation From Tandem Cylinders with Different Diameter

Aerodynamic noise generated by various technical applications, such as parts of the landing gear of aircraft or protective grilles for axial fans, can be investigated in a simplified manner by using two circular cylinders in a tandem configuration. Although a variety of experimental and numerical studies exists on such configurations, the effects of unequal cylinder diameters on the resulting far-field noise generation are not fully understood, especially for varying distances between the cylinders. With the aim of providing a substantial experimental data set and to allow for preliminary investigations of possible scaling approaches, a detailed wind tunnel study was performed on a set of two-dimensional circular cylinders with diameters from 6~mm to 40~mm in a tandem arrangement. Different normalized distances were investigated, using a nominal diameter of 30~mm as a reference. Acoustic measurements were performed using a set of free-field microphones located in the acoustic far field. The results indicate that for configurations with a thicker upstream cylinder, the vortex shedding and the subsequent generation of tonal noise are governed by the flow around the upstream cylinder. For configurations with a thicker downstream cylinder and small normalized spacing, the vortex shedding scales with the diameter of the downstream cylinder.