Velocity measurement of near-wall flow over inclined and curved boundaries by extended interfacial particle image velocimetry

Particle image velocimetry (PIV) measurements near a curved boundary usually require efforts to deal with low tracer density, high shear gradient and wall reflection. To resolve these difficulties, we presented a near-wall measurement technique named interfacial PIV (IPIV) that could return a tangential velocity component and a tangential component of wall gradient [Nguyen TD, Wells J, Nguyen C. Wall shear stress measurement of near-wall flow over inclined and curved boundaries by stereo interfacial particle image velocimetry. International Journal of Heat and Fluid Flow 2010;31(3):442-9]. In this paper, we introduce an extension of IPIV to measure the tangential and wall-normal velocity components. This extension allows IPIV to obtain three velocity components when IPIV is applied to stereoscopic PIV images of flows over inclined and curved boundaries. The performance of IPIV is validated against a particle image distortion (PID) technique using synthetic images generated from a direct numerical simulation velocity field of a turbulent flow over a wavy wall. Results show that IPIV is more accurate than PID in the near-wall velocity measurement. Practical applications of IPIV to experimental images of open flume tests with a wavy wall and a backward-facing step are described.