Extracting sound from flow measured by parallel phase-shifting interferometry using spatio-temporal filter

We have proposed a method of simultaneously measuring aerodynamic sound and fluid flow using parallel phase-shifting interferometry (PPSI). PPSI can observe phase of light instantaneously and quantitatively. This method is useful for understanding the aerodynamic sound because PPSI can measure near the source of the aerodynamic sound. However, the components of sound and flow should be separated in order to observe detail near the source of sound inside a region of flow. Therefore, we consider a separation of the component of sound from simultaneously visualized images of sound and flow. In previous research, a spatio-temporal filter was used to extract a component satisfying the wave equation. The flow and the sound are different physical phenomena, and the flow cannot be expressed by the wave equation. Hence, we think that the spatio-temporal filter enables us to separate the component of sound from the simultaneously visualized images. In this paper, we propose a method for separation of flow and sound using spatio-temporal filter in order to visualize the component of the aerodynamic sound near its source. We conducted an experiment of the separation of data measured by PPSI. The results show that the spatio-temporal filter can extract the sound from air-flow except for the sound near objects and boundaries.