Application of particle image velocimetry for velocity measurements in subsonic near-wall shear flows

Particle Image Velocimetry (PIV) is widely used in experimental studies on fluid mechanics making it possible to observe panoramic instantaneous velocity distributions. In the present work we consider application of PIV for investigation of the flow details in boundary layers with respect to two particular topics. The first of them is determination of the local skin friction coefficient of turbulent boundary layer. To this end, measurements of the linear part of the mean-velocity profile in the viscous sublayer can be used in non-equilibrium flows. Meanwhile, hot-wire anemometry is not appropriate in this case due to the cooling effect of the neighbouring wall on the hot-wire readings. For PIV measurements in the sublayer, a sophisticated technique is usually needed including the use of long distance microscopes, special calibration procedures, seeding particles and software. The second point is reliability of PIV in experiments on laminar-turbulent transition in shear layers. Normally, the method provides a sufficient resolution of rather strong velocity variations. Also, during transition to turbulence, it was found as a suitable technique to observe velocity perturbations as low as ~ 10–2 of the free stream velocity, e.g.. In the present paper we are interested in potential application of PIV for investigation of much weaker laminar-flow disturbances found at the early stage of transition to turbulence