Use of the POD and the Coherent Structure Detection Criteria to Study the Flow Dynamics Downstream a Confined Square Obstacle

International audienceStudying the concept of the vortex is an essential tool in the comprehension of fluid dynamics. Despite this, it is still very difficult to find a universal definition of a vortex. Several methods of detection and characterization of vortex structures has been developed and performed. Specifically tailored for PIV data, they present an important topic in modern experimental fluid mechanics. In fact, the performance of the method is related to its effectiveness in the velocity data analysis and to successfully detect and locate the vortices as well as calculate the characteristic vortex parameters. In the present study, we explore the efficiency of different vortex detection algorithms such as the vorticity ω, Γ2 and Q criteria by studying the vortices structures in the wake of a confined square obstacle. Proper orthogonal decomposition (POD) of the velocity fields was used to extract the energetic contribution of the different instabilities modes. These methods were firstly applied to an experimentally two-dimensional instantaneous velocity fields obtained by Particle Image Velocimetry (PIV) technique. Then, in a second step, we tested these criterions on a numerical velocity fields determined from Lattice Boltzmann simulations and compared to experimental results