Experimental Detection of Large-Scale Flow Structures in Rayleigh–Taylor instability

Here we examine the large-scale structures that develop in Rayleigh–Taylor instability (RTI) experiments. Our experimental setup is comprised of two layers of fluid separated by a polycarbonate barrier at mid-depth of an acrylic tank. A statically unstable stratification is set up across the barrier such that when the barrier is removed RTI develops. Velocity and density data are collected using simultaneous particle image velocimetry and planar laser induced fluorescence.



Large-scale structures are found using a Lagrangian-filtering based technique, which allows us to divide the flow into two structure fields b⁺ (downward moving) and b^- (upward moving). The experimentally determined b^± fields show reasonable agreement with previous numerical work and the mean per-structure average profiles show good agreement with theoretical predictions from two-fluid two-structure models. Thus, providing physical evidence for their existence across the mixing zone.