Use of Blowing Flow Control to Reduce Bluff Body Interaction Noise

When an unsteady wake from an upstream body impinges on a downstream body, the resultant interaction noise can be significant. The use of distributed blowing through the surface of a cylinder to reduce this source of noise was investigated experimentally. Two configurations were tested, one with a cylinder upstream of an H-beam (denoted the OH configuration) and the other with an H-beam upstream of the cylinder (denoted the HO configuration). The mean velocities and velocity fluctuations were determined in the flowfield using particle image velocimetry. The application of blowing to the OH configuration reduced the streamwise Reynolds stress (u'u'). This resulted in a noise reduction of 9.2 dB at a Strouhal number (St) of 0.2. There was a broadband noise reduction of 3 dB averaged over a Strouhal number range 0.05 < St < 5. The effect of blowing on the HO configuration was to inhibit the strong crossflow Reynolds stress (w'w') between the H-beam and the cylinder. This resulted in a noise reduction of 15 dB at a Strouhal number of 0.8. There was a broadband noise reduction of 4.6 dB averaged over the frequency range 0.05 < St < 6.3. The effect of blowing produced additional high-frequency noise. This additional noise was minimized with blowing applied through a sintered plate with a very small pore diameter.