Identification of nonlinear characteristics of thermoacoustic oscillations in helium piping systems

摘要

Insufficient dynamic information on helium piping systems limits our ability to understand and identify thermoacoustic oscillation (TAO) phenomena in these systems. In this study, we investigate the associated oscillation behaviours and the effects of the temperature distribution steepness, S, and the inflection point position, x_0, on the TAO characteristics through numerical simulations. The results indicate that x_0 has a greater impact on the oscillation behaviour and is a decisive factor for oscillation-free operation. It is found that oscillation-free operation can be achieved when x_0 = 0.9 m. To identify the nonlinear dynamic characteristics related to TAO, the original pressure time series are unfolded in phase portraits and Poincare maps. In contrast to the period-1 and period-2 limit circle oscillations at other positions, the trajectory at x_0 = 0.9 m displays a transition from limit circles to a fixed point (zero amplitude), corresponding to a series of points including the point (0,0) in the Poincare map. Therefore, an approach of adjusting the inflection point position can be used to control the state of the TAO, and the transition in the nonlinear dynamic characteristics can be identified, which can also provide guidelines for designers to mitigate unfavourable TAO.