Particle Image Velocimetry (PIV) for measurement of the acoustic particle velocity
Non-intrusive measurements of the acoustic particle velocity under realistic flow conditions can be performed by means of a synchronized PIV technique. Acoustic PIV (A-PIV) is an acoustically extended PIV technique with the data acquisition synchronized to the acoustic-excitation signal and an appropriate post processing. Within an acoustic-excitation period, the acquisition of PIV images is successively triggered at several equidistant phase angles. This technique provides the measurement of sound frequencies far above the data acquisition rate of 10 Hz of a commercial PIV system. The left image shows an example of a planar measurement of the acoustic particle velocity in the vicinity of a Helmholtz-resonator liner. This kind of liner is used as acoustic absorber e.g. in inlets of aero engines. The right picture demonstrates the time-resolved propagation of a higher acoustic mode, which was detected by means of a three-dimensional A-PIV measurement in a rectangular test duct.
Axial component of the acoustic particle velocity of a higher order mode.
Measured acoustic particle velocity in above a Helmholtz-Resonator-Liner.