Stereoscopic particle image velocimetry measurements of supersonic, turbulent, and interacting streamwise vortices: challenges and application

This work presents a comprehensive review of the challenges encountered in stereoscopic PIV measurements when applied to the characterization of complex and interacting systems of turbulent supersonic streamwise vortices. Emphasis is given to the proper selection of critical parameters, their impact on the observability of the flowfield of interest and the accuracy of the derived results. Specifically, the discussion is centered on the guidelines underlying the requirements related to the choice of the interrogation area, laser pulse separation time and flow tracers in response to the necessity to probe the coherent structures under the constraints imposed by the investigated flow. Peak locking and its impact on the accuracy of the experiment are addressed and indications are given on how to recognize the resulting errors. All the aforementioned parameters are also analyzed with respect to each other as an ideal selection of some of them often produces contrasting effects on the others, affecting the calculations of the flowfields. The design and the results of a stereoscopic PIV experiment for the characterization of interacting, turbulent streamwise vortices in a Mach 2.5 freestream are included in this work in order to provide a practical application of the selection process of the critical experimental parameters and highlight the identification of the aforementioned contrasting requirements. (C) 2013 Elsevier Ltd. All rights reserved.