Modeling of miniature pulse combustors for active flow control

Miniature valveless pulse combustors ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="script">O</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> ) are small-scale thermoacoustic engines that generate high-momentum periodic jets, making them promising actuators for active flow control. These devices function without moving parts, relying on thermoacoustic oscillations in which unsteady heat release is synchronized with the acoustic field to sustain a limit cycle. This study presents a low-order thermo–electro–acoustic network model that integrates the Rott–Swift viscothermal formulation with a Crocco n – τ flame transfer function. Monte Carlo screening is applied to uncertain flame parameters to identify geometries that maximize unsteady jet output. Model predictions are validated using a miniature combustor equipped with pressure and force sensors, enabling a coherence-weighted thrust analysis that isolates combustion-driven performance. The results indicate that effective operation is achieved when length-dependent electro-acoustic modes, including throat acoustic and chamber Helmholtz modes, converge with the dominant intrinsic thermoacoustic (ITA) family. This convergence reflects a balance of throat inertance, chamber compliance, and flame dynamics consistent with the Rayleigh criterion. Harmonic and sum-tone interactions further reinforce acoustic branches, while shear-layer tones remain secondary. For three throat diameters, the predicted amplification windows agree with the measured coherence-weighted thrust RMS peaks and the eigen-map coincidence regions.