Some Attempts on Characterization of Turbulent Wakes Observed by Using Stereo PIV in a Plane Perpendicular to The Flow

The turbulent wake behind a bluff body is a significant flow phenomenon. It is closely linked to drag generation, can induce structural vibrations, influences downstream bodies, and enhances mixing and heat transfer. The instantaneous cross-section of the wake can be measured using Particle Image Velocimetry (PIV). A commonly employed setup is Stereo PIV, which observes a plane perpendicular to the flow. This study aims to develop a simple method for characterizing the instantaneous wake section for comparative purposes. The focus is on wake meandering, which cannot be captured by analyzing mean velocity fields alone. Two approaches are compared: (i) identifying regions where velocity falls below a chosen threshold, and (ii) fitting the velocity field with a symmetric Gaussian peak. The test case for comparing those two approaches is the wake past Lego part no. 2418, which appears in two configurations: with a hole on the top or without this hole; additionally, the case with a round cap typical for Aquazone is tested. The sensitivity of both methods to subtle changes in wake dynamics is evaluated. The observation is that the hole and the cap have only a negligible effect on the wake meandering.