Transition from laminar to turbulence in porous media requires highly resolved observations along with investigation of the complex flow physics within the pores. Of specific interest is introducing a general criteria capable of predicting the onset of turbulence in different porous arrangements. In spite of many contributions in laminar cases, the physics behind cases exceeding the steady laminar has not been well identified. Hence, some questions may arise about this phenomenon. We are motivated to answer if there are certain broadly-applicable flow characteristics as demarcation criteria that are major contributors in transition regime within a porous system. In other words, what makes the whole bed turbulent when only very few pores are representing turbulent behavior. From a better perspective, studying the turbulence growth spatially and temporally in the whole porous bed from Eulerian aspects is of interest. There is also a fact in steady flows that fluid elements undergo chaotic trajectories if the media has a random structure. Recognizing the nonlinear physics emerging beyond the limits of Darcy regime has been a motive for numerous studies to show a universal description for interpreting the behavior of high velocity flow regimes inside the pores.
Yet, a general widely-accepted basis is lacking in transitional and turbulent flows in permeable media. The complex geometry, as well as limited experimental interrogation over-complicates the experimentation in this field especially for turbulent flows. In this work, two-component Time-Resolved Particle Image Velocimetry (TR-PIV) technique is employed to visualize the flow. Capturing velocity field, and measuring the flow structures as well as the turbulent characteristics in transition from laminar to turbulence within a mono-dispersed randomly packed bed of spheres is a cruicial part of this research. Critical point analysis of vortical structures and their growth within a range of pore Reynolds numbers (100-1000) are applied as the preliminary stage of studying the evolution of inertial effects in transition regime. The identified scales associated with the vortical elements are compared based on Reynolds number and pore geometry. The common Eulerian approach in characterizing the turbulent flow is applied to this flow field in order to find characteristics such as scales, production, dissipation, and kinetic energy. The common turbulence characterization methods are compared with critical point analysis for comparing their performance in determining the onset of turbulence in porous media.