Flow/Acoustic Interactions for Two Cylinders in Cross Flow

The noise generated by two cylinders placed in tandem (i.e. the second in the wake of the first) has been investigated for spacings of 5, 4 & 3 diameters. Measurements of turbulence were obtained between the two cylinders and of fluctuating pressure for the near field region for these cylinder spacings using a microphone with a nose cone. Turbulence levels in the test section were varied using a grid upstream and tests were conducted at different flow velocities and incident levels of turbulence. Although, for a number of cases, up to four peaks related to vortex shedding were evident in the spectrum, most measurements exhibited two peaks, a dominant one at the vortex shedding frequency with a secondary peak at twice this value. The measurements show that the vortex noise is strongest at the mid point between the cylinders and at the rear cylinder with levels of 130 dB. The harmonic component was strongest at the downstream cylinder where peak values of 110 dB were obtained.