Random sound pressure fluctuations Induced by non-linear damping in a reactor column

Abstract

Self-excited non-harmonic oscillations due to non-linear damping in the system are produced in a reactor column. The uniform steady flow is converted spontaneously into random fluctuations in sound pressure, under the especial experimental conditions, in a reactor column that includes a thin layer of dissipative porous medium. The resulting large-amplitude non-harmonic pressure fluctuations in the air-flow are similar to the bifurcation in chaotic systems; where two or more energy states can occur simultaneously, and the system oscillates between them. Experimental results demonstrate this abrupt change in flow-regime, from steady-flow to random fluctuations. Our results show that a low-pressure shock-wave- is established that precedes the self-excitation fluctuation in the system. Results also show the existence of a threshold for flow-velocity beyond which this transition from steady to pulsating non-harmonic pressure fluctuations occur. A numerical model is developed for this behavior in terms of; FFT peak frequencies, flow-velocity, characteristic numbers, relaxation-time, and system nonlinear damping.