"Profile-PIV" - More than just an optical hotwire: New potentials of particle image velocimetry in boundary layer research

Abstract

The ISFV Asanuma Award lecture was held by the author during the 18th International Symposium of Flow Visualization held in Zurich, Switzerland, in June 2018. It provided an overview of the development, implementation and application of a recently developed variant of the particle image velocimetry (PIV) technique. The so-called "profile-PIV" approach utilizes high aspect ratio image formats to capture velocity data along narrow strips rather than providing the nearly square flow maps characteristic of PIV. Using a high-speed camera, the smaller image format allows the image capture at frame rates up to and beyond 100 kHz such that converged velocity statistics become feasible when using sample counts of similar magnitude. The narrow field of view permits a proportional reduction of the laser power required for particle illumination. For medium speed air flows (U < 10 m/s) a CW laser is suitable, whereas pulsed diode lasers are required at higher velocities. When operated with high image magnification near 1:1, the technique provides access to near-wall velocity statistics of boundary layer flows, in particular, to recover the mean and unsteady wall shear stress, even at higher shear Reynolds numbers, provided the viscous scales can still be resolved by the imager's pixels. The potential of the "profile-PIV" technique is demonstrated with examples from a variety of recent applications is given, mainly in the area of turbulent boundary layer investigation.