Shocked and unshocked thermoacoustic oscillations in a looped tube

Experiments are performed to demonstrate emergence of shocked and unshocked thermoacoustic oscillations in a circular, looped tube filled with an atmospheric air. A pair of stacks identical in geometry is installed at diametrically opposite positions, and each stack is sandwiched by hot and cold heat exchangers. The hot heat exchangers are heated by electric heaters evenly for the same temperature gradient to be imposed on the stacks. The cold heat exchangers are cooled by circulating a tap water to be kept at an ambient temperature. Four types of the stacks are employed to examine influences of stack’s pore width and its porosity on the oscillations. For all stacks, self-excited thermoacoustic oscillations are observed, which propagate in the same sense as the one of the temperature gradient. The oscillations occur in a 1-wave mode where the wavelength corresponds to the loop length. The maximum of the peak-to-peak acoustic pressure is found to attain 15% relative to the atmospheric pressure. Depending on the pair of stacks, shocked or unshocked profiles are observed. Difference in mechanisms leading to the two profiles is examined from a viewpoint of dissonance of eigenfrequencies of the oscillations.Experiments are performed to demonstrate emergence of shocked and unshocked thermoacoustic oscillations in a circular, looped tube filled with an atmospheric air. A pair of stacks identical in geometry is installed at diametrically opposite positions, and each stack is sandwiched by hot and cold heat exchangers. The hot heat exchangers are heated by electric heaters evenly for the same temperature gradient to be imposed on the stacks. The cold heat exchangers are cooled by circulating a tap water to be kept at an ambient temperature. Four types of the stacks are employed to examine influences of stack’s pore width and its porosity on the oscillations. For all stacks, self-excited thermoacoustic oscillations are observed, which propagate in the same sense as the one of the temperature gradient. The oscillations occur in a 1-wave mode where the wavelength corresponds to the loop length. The maximum of the peak-to-peak acoustic pressure is found to attain 15% relative to the atmospheric pressure. Depending o...