Figure 1 shows the results of a measurement of the celerity or acoustic particle velocity via a PIV system for a rectangular duct. A single frequency excitation signal is released by a loud speaker connected directly to the test section.
Figure 2: Two vector maps respectively calculated out of two PIV images are recorded with 180° phase shift, in result the celerity has opposite sign.
Finally the acoustic particle velocity is derived in the data post processing by subtracting two successive vector fields.