A flow-intrinsic trigger for capturing reconfigurations in buoyancy-driven flows in automated PIV

In order to acquire flow fields of rare reconfiguration events in buoyancy-driven flows, an automated flow-intrinsic trigger method for 3D particle image velocimetry (PIV) was developed. The trigger condition for initiating PIV is based on continuous multi-probe temperature measurements. The autonomously started PIV was realized with LED illumination and a controlled helium-filled soap bubble generator. The measured velocity fields reveal the transition between two different flow states in a mixed convection sample as proof of concept for this method. It is further proposed to consider the time series of all temperature probes for the trigger condition using Proper Orthogonal Decomposition (POD). It is demonstrated that the use of this POD-based trigger condition allows to detect flow events much earlier than the trigger based on single raw temperature signals.