Abstract
In microscopic particle image velocimetry (micro-PIV), correlation averaging over multiple frames is often required, leading to a loss in temporal resolution, therefore limiting the measurement accuracy for unsteady flows. Here, we present a new PIV method suitable to study steady and unsteady laminar flows between parallel plates (i.e., Hele-Shaw flow), which is a common flow configuration in microfluidic applications. Our method reduces the effective seeding density and yields similar if not higher signal-to-noise ratio (SNR) compared to conventional micro-PIV. We call this algorithm Psi-PIV. Psi-PIV requires a much smaller number of frames to reach the same SNR compared to the widely used correlation averaging method. This leads to a significant improvement of the temporal resolution. The Psi-PIV algorithm is used in an experimental investigation of steady and unsteady flows in a Hele-Shaw cell. Our experiment shows that Psi-PIV reduces the number of required frames by 8 times and 30 times compared to the frames required by conventional PIV for steady and unsteady laminar flow, respectively. In this study, PIV and Psi-PIV use a single-pass cross-correlation to present the underlying difference between the two approaches.Graphic abstract
Highlights
Microscopic particle image velocimetry differs from conventional PIV in two main aspects (Adrian and Westerweel 2011; Lindken et al 2009; Wereley and Meinhart 2010): (1) the image density is usually much lower, NI ≤ 1 and (2) the entire measurement volume is illuminated, rather than a thin light sheet
NF helps in building up the spatial correlation by the superimposition of the correlation data from the image density of each pair multiplied by the number of frames in the recording sequence
The valid detection probability of synthetic data as a function of effective image density Neff shows that a higher signal-to-noise ratio (SNR) can be achieved by Ψ-PIV compared to conventional PIV
Summary
Microscopic particle image velocimetry (micro-PIV) differs from conventional PIV in two main aspects (Adrian and Westerweel 2011; Lindken et al 2009; Wereley and Meinhart 2010): (1) the image density is usually much lower, NI ≤ 1 and (2) the entire measurement volume is illuminated, rather than a thin light sheet. In the case of a HeleShaw flow cell where the measurement volume includes the full height of the cell and the variation of the velocity spans the full parabolic velocity profile, it is necessary to use much more than 100 frame pairs for the correlation averaging (Ehyaei and Kiger 2014). This makes it very difficult to apply micro-PIV to unsteady microfluidic flows
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