High-speed centrifugal blower for experimental aeroacoustics

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The vortex-shedding phenomenon has been a subject of research since it was observed by Leonardo da Vinci. Vortex shedding occurs due to the boundary layer separation around bluff bodies in cross-flow. The boundary layer separates into two shear layers that trail and roll-up in the near field forming a periodic vortex street. In the case of a duct containing a bluff body such as a circular cylinder, when the vortex shedding frequency coincides with one of the acoustic natural frequencies of the duct, a feedback cycle may occur where the vortex shedding acts as a sound source and excites an acoustic standing wave which, in turn, enhances the shedding process and thereby creates a strong acoustic resonance. This process is known as flow-excited acoustic resonance. In many engineering applications where ducts containing clusters of bluff bodies are encountered, such as tube bundles of heat exchangers and boilers, cascades of compressor blades and guide/turning vanes in ducts and radial diffusers, unfortunate operating conditions could lead to a coincidence between the vortex shedding frequency and one of the acoustic natural frequencies of the duct. This often leads to flow-excited acoustic resonance and the generation of acute noise problems and/or excessive vibrations. Since this phenomenon is not yet fully understood, it can be dangerously unpredictable and may cause catastrophic failures in many applications such as power generation and transport. The main objective of the applicant's research in this area is to understand the feedback cycle of the flow-excited acoustic resonance. This requires the generation of a self-excited acoustic resonance in flow configurations similar to those mentioned above. However, the self-excited acoustic resonance will not materialize unless the flow velocity is sufficiently high to overcome the losses due to acoustic damping.This can only be achieved using the requested centrifugal blower system, which is capable of producing air flow with a velocity as high as 220 m/s in a cross-section area of 10 inch (25.4 cm) by 10 inch (25.4 cm).