New development in near-wall PIV measurements

Abstract

Very recently, obvious advances have been made in fluid mechanics theoretically [1-6]. The progress of experiment and related method is also worthy of attention. The detailed physics of a near-wall flow is essential for understanding the flow behavior. Very near-wall measurement is widely considered as one of the major technical challenges for fluid mechanics studies, which have a great significance for practical engineering designs and fundamental scientific researches. At present, accurate particle image velocimetry (PIV) measurements very near the wall are still a great challenge. For the measurements near fluid/solid interfaces, Prof. CB Lee and his research group at PKU developed a novel image parity exchange (IPX) technique by adding optimal synthetic particles (OSP) on the solid side in order to get better flow velocity measurements in the near wall region [7]. The improved image-preprocessing method expands the traditional window deformation iterative multigrid scheme in PIV image processing with very large displacement commonly encountered in the measurements of hypersonic boundary layers. Before performing interrogation operation, stationary artificial particles of uniform size are added in the near wall region on the solid side. The initial estimation near the interface is then smoothed by the measurement data from both sides of the interface in order to reduce the large random uncertainties. Interrogations in the following iterative steps converge to the correct results to provide more accurate estimations for particle tracking velocimetries.