Flow visualization in a hybrid thermoacoustic system

Abstract

An experimental investigation is conducted to understand the flow behavior near a stack in a hybrid thermoacoustic system including resonator and looped-tube. Time-resolved particle image velocimetry measurement is applied to obtain the evolution of the local oscillating flow. Phase-averaged results show two types of vortices in the flow field due to the stack: the primary vortices attaching at the end of stack, and the corresponding secondary vortices propagating with the base flow. Proper orthogonal decomposition is applied to illustrate small-scale fluctuations from the main flow structure. The temporal coefficients show that vortical flow structures vary from one cycle to another, consistent to the great increment of the phase-averaged turbulence kinetic energy during the period with vortical flow structures. With the same input power, the momentum fluctuation is larger at harmonic frequencies. At the same frequency, the turbulence level is nonmonotonic to the input power although the momentum fluctuation increases with the input power.