Digital In-line Holographic PIV for 3D Particulate Flow Diagnostics

We present a digital in-line holographic PIV system for diagnosing 3D particulate flows. This system records in-line holograms directly to a CCD camera and reconstructs them numerically. Since the pixel resolution of CCD cameras is much lower than that of holographic films, conventional particle extraction methods cannot yield high depth resolution that is important for velocity measurement and particulate flow diagnostics. To solve this problem, we have developed a novel particle extraction method based on the complex amplitude of reconstructed wave. With a simple in-line recording setup, this method can reach a depth resolution that is comparable with that of some off-axis holographic PIV systems. This method also alleviates the speckle noise problem intrinsic to in-line particle holography since speckles and particles can be clearly differentiated in complex wavefield. This technique is the basis for a digital in-line holographic PIV (HPIV) system with the addition of Concise Cross Correlation (CCC) and particle pairing algorithm (Pu and Meng 2000). Details of the system hardware and data processing method are described in this paper. The system was tested by both a simulated 3D flow around a collapsing spherical cavity and a laboratory particle suspension.