Oscillating and streaming flow identification in a thermoacoustic resonator, from undersampled PIV measurements

The nonlinear phenomena that appear in thermoacoustic systems generate continuous secondary flows (streaming), superimposed on the dominant acoustic oscillations, reducing system efficiency. In this paper, an experimental study is presented for evaluating both acoustics and streaming in such a system. The velocity measurements, based on particle image velocimetry, are undersampled with respect to the acoustic period and without external phase reference. A new method is proposed for treating the undersampled data, in which the acoustic field is reconstructed via an embedding technique. The application of this method and use of different data processing tools provide results in good agreement with linear acoustic theory. The harmonic content of the velocity as well as the wavelength are obtained. The estimate of the mean velocity over the time period indicates the existence of a continuous flow different from the Rayleigh–Schlichting streaming. (paper)