Correlation-based algorithms for accurate PIV measurement near the slip boundary

Abstract

Accurate particle image velocimetry (PIV) measurement near the wall is of great significance in many fields. However, it is challenging for conventional PIV algorithms to deal with the near-wall flow, especially under the slip boundary condition. In general, the conventional window correlation method cannot accurately calculate the flow velocity at any location that is less than half the size of the interrogation window away from the boundary. For steady or periodic flow, the single-pixel ensemble correlation method can estimate the velocity very near the wall, but numerous image pairs are required, which comes at a great computational cost. In this paper, a new method based on window deformation is proposed to estimate the velocity profile of near-wall flows. Furthermore, a multi-pixel ensemble correlation method is proposed based on the single-pixel method, which improves accuracy and significantly reduces the computational cost relative to the single-pixel method. Both methods are validated by synthetic particle images and experiments. The present work extends the PIV methodology for accurately measuring near-wall flows, especially under the slip boundary condition, which will benefit research on the boundary layer, drag reduction, microfluidics, etc.