Numerical investigation of a Y-shaped thermoacoustic combustor with a Helmholtz resonator implemented and operated at off-design conditions

Abstract

Self-excited thermoacousitc instability is undesirable in propulsion and gas turbine engines. To attenuate these instabilities, Helmholtz resonators shaped like a beer bottle are typically applied to dampen combustion-driven acoustic oscillations. The damping effect is maximized at resonance, since large volume of fluid in the cavity volume compresses and expands periodically, while a mass of the fluid in the resonator neck oscillates. Such periodic motions lead to thermos-viscous and vortex shedding losses. In this work, two-dimensional numerical studies on a Y-shaped thermoacoustic combustor with a Helmholtz resonator attached are conducted to shed lights on the damping performances of the resonators at off-resonance conditions. The Y-shaped system has a mother stem at the bottom. It splits into 2 bifurcating upper branches with different lengths corresponding to 2 non-harmonic longitudinal modes. Premixed propane and air are burnt in the bottom stem. The effects of the off-design conditions achieved by varying the resonator cavity volume on the limit cycle oscillations and the combustion products are examined in details. It is found that when the mass flow rate oscillation amplitude at the neck is increased by 1500%, the acoustic pressure amplitude is reduced by 20%. However, the dominant and secondary mode frequencies are almost unchanged.