Search

An experimental investigation has been carried out for the flow-induced sound in a grooved circular pipe. The length of the pipe is 500 mm, the inner diameter is 23 mm and the groove pitch is kept at 8 mm. The velocity in the pipe is varied from 6 m/s to 66 m/s. In the region of the velocity smaller than 30 m/s, the frequency of the sound generated in the pipe increases in the shape of stairs with increase of the velocity, and then resonant sound of the pipe generates from the pipe. When the velocity becomes large, the frequency of the sound increases linearly to the velocity. The shape of change of the frequency can be explained from characteristics of a cavity flow and lock-in phenomenon by the resonant frequency of the pipe.

The self-excited tone of a circular jet impinging upon a coaxial pipe can be give rise to not simply a single, however as many as well-defined frequency components in the rage of Reynoldsnumber (based on initial momentum thickness and jet velocity) 171gReg271. All of these components are traceble to the nonlinear interraction frequency of two primary components : the most stable frequency of the jet shear layer, β, and a low-frequency modulating component, β/2. The modulating component β/2 arises from vortex-vortex interaction at the impingiment edge. Its upsteram storongly modulates the sensitive regime of the shear layer at the nozzle lip. The most stable component can become sudden change (i.e. frequency down) when it is coincided with resonance of the air column in pipe.