Application of Time-Resolved Particle Image Velocimetry Measurement to Vortex Flow Measurement

The generation of vortex flow in an incompressible fluid inside a rotating closed aquarium of cubic shape was experimentally investigated. The flow excitation was achieved by creating small-scale vortices near the lateral edges of the cube. Two operation modes of the setup were studied, namely: the injection of turbulence inside the reservoir leading to its transition to a statistically stationary state and the relaxation of turbulent flow from a stationary state. Characteristics of the emerging flow were examined, including: the energy dependence on time, the energy spectrum of the system on the wave vector at different time points, the Reynolds macro-number dependence on time, the Rossby micro-number dependence on time, and the number of vortices over time. It was demonstrated that the existing PIV algorithm introduces an error in determining the flow velocity in the first order with respect to time, resulting in a systematic error when measuring secondary flow in long-lived quasi-two-dimensional vortices. The PIV algorithm was successfully modified to the second order with respect to time.