58691 - On the Effect of Noise Induced Dynamics on Linear Growth Rates of Oscillations in an Electroacoustic Rijke Tube Simulator 

  Controlling the occurrence of self-excited thermoacoustic oscillations continues to be one of the milestones in lean premixed gas turbine combustors. A known strategy to reduce these oscillations is to implement acoustic damping devices. For designing of such devices, estimation of deterministic parameters characterizing the acoustic-flame coupling, specifically linear growth rates are essential. Gas turbine combustors are typically noisy environments. These systems are driven by a robust stochastic forcing resulting from highly turbulent reactive flows and unsteady combustion. Four different approaches based on Van der Pol equation were proposed by Noiray and Schuermans (Int. J. Nonlin. Mech., 50 2013) for system identification in linearly stable and unstable systems. In the present work, we use these approaches for an electroacoustic Rijke tube simulator developed for mimicking acoustic-flame interactions. We estimate the growth rates from noisy limit cycle data and investigate the effect of two control parameters: non-dimensional heater power and additive noise intensity.

   Through comparison between experiments and numerical simulations, we propose that noise influences the values of growth constants and shift the stability boundaries of a dynamical system. We quantify our results by producing a subcritical Hopf bifurcation diagram based on the extremum values of stochastic probability density function (SPDF). In the subthreshold region, we observe that the system responds to external acoustic noise indicating the presence of coherence resonance. This study shows that noise (up to triggering amplitude) can enhance the bi-stable region. The study proposes a step forward in thermoacoustic field for control of large amplitude acoustic oscillations.