Compressible flow of liquid in standing wave tube

Particle Image Velocimetry (PIV) has been applied to the study of acoustic flow of liquid in standing wave tube. Even though liquid compressibility is very small, the liquid must be treated as compressible in this case. With the finite compressibility of liquid in mind, a series of different standing wave modes can be formed in the tube by pressure waves emanated from the bimorph piezo disk at the end of the tube, at some specific driving frequency. In this paper, the first three natural standing wave modes were visualized by using 1 mum diameter fluorescent microspheres seeded in the liquid. The variation of flow field in the acoustic boundary layer near the wall was measured using PIV. Water was first used as a working fluid. Experiments were also carried out with glycerol-water mixture (50%--50% by volume) to examine the effect of viscosity change on the wave propagation and flow structure inside the tube. The experimental results are also compared with theoretical model predictions.