A stereoscopic PIV system for the Princeton Superpipe

Herein, we describe the design and testing of a stereoscopic PIV system uniquely adapted for the high pressure environment of the Princeton Superpipe. The Superpipe is a recirculating pipe facility that utilizes compressed air as the working fluid to attain very high Reynolds numbers. Commercial piping is used as the pressure vessel to hold pressure up to 220 bars, and a test pipe is enclosed inside with a development length of 200 diameters that ensures a fully-developed condition at the test section. The highest achievable Reynolds number (based on the bulk velocity and the pipe diameter) is 35×106, corresponding to a maximum friction Reynolds number of 5×105. The unprecedented range of Reynolds number has enabled a number of new insights in the behavior of high Reynolds number wall-bounded turbulence (Zagarola and Smits, 1998; Hultmark et al., 2013). However, past measurements in the Superpipe have been primarily restricted to single-component, one- or two-point statistics of fully-developed pipe flows. The present work aims to expand the capability of the Superpipe to study turbulent coherent structures and multi-point statistics by means of a new stereoscopic PIV system. The high pressure environment and the confined space inside the pressure vessel pose challenges to both imaging and seeding, the solutions to which will be discussed.