NATURAL FREQUENCIES IN PIPES WITH ORIFICE TERMINATIONS

摘要

Acoustic resonance frequencies help identify which pipe segments in a complex piping system are likely to undergo forced vibration. This study focuses on a pipe with a sinusoidal pressure disturbance imposed at one end on an otherwise steady flow, with the other end of the pipe terminating at an orifice. In order to determine the natural acoustic frequencies of this scenario, it is not obvious whether to model the boundary condition at the orifice as an open or closed pipe, or somewhere in between. The results of this study show how the natural frequencies in a pipe segment are related to the loss coefficient K in three different categories. First, when K is less than C/V, where C is the speed of sound and V is the mean fluid velocity, the natural acoustic frequency resembles that of an open pipe, with the amplitude that grows to a limiting value. Second, when K is greater than C/V, the natural frequency corresponds to a closed pipe, and the amplitude also grows to a limiting value. Lastly, when K is equal to C/V, disturbance will propagate to the orifice without exciting a resonance as if the pipe were infinitely long.