Experimental instability study in a thermoacoustic prime‐mover

An experimental linear stability study of a thermoacoustic prime‐mover is performed for different values of the mean pressure between 0.5 and 10 bars. The damping rate is carefully obtained as a function of the temperature gradient |∇T| enforced along the stack, up to the instability onset at |∇T|c. These results are then confronted with the predictions of a numerical model based on Rotts’ theory used with complex frequencies, in which the prime‐mover is seen as a feedback loop in the electrical analogy. The experimental results are found to reasonably comply with Rott’s theory as soon as the mean pressure exceeds 2 bars. Below this value substantial discrepancies are found, as confirmed by the work of Yazaki. Above the instability onset, the saturated wave amplitude is measured as a function of |∇T|−|∇T|c for fixed pressure. The bifurcation to the nonlinear saturated wave has been tentatively determined as subcritical, although thermal inertia effects make it look supercritical.