Graduate Thesis Or Dissertation
 

Vortical Structures in Transition to Turbulence through Randomly Packed Porous Media: Scale, Energy, and Mixing Characteristics

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/70795f916

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  • Vortical structures are the driving mechanism of transition to turbulence in porous media requiring adequately resolved observations along with analysis of the scale and energy of flow within the pores. Of specific interest is to understand the vortex dynamics, energy, and turbulent mixing and transport properties in the scale of each pore and overall throughout the entire permeable media by enhancing the inertial effects with Reynolds number. Transition to turbulence, a general problem in porous media flows, is influenced by random tortuous geometry generating complex flow structures. In spite of many contributions in laminar cases, the vortical physics behind cases exceeding the steady laminar flow has not been well investigated. Major questions are categorized as follows: (a) how does the global (macro-scale) mean velocity influence the local (pore-scale) vortical flow structures,(b) what are the dominant mechanisms for energy growth emanated from swirling motions as opposed to turbulent kinetic energy, and (c) how does the inertial effects of vortical structures enhance the flow mixing and transport in randomly packed porous media. Investigating the proposed problems, we implement high fidelity velocimetry experiments: (1) to estimate the scale of vortical flow structures in terms of size, time, and number density that are major contributors in transition regime locally in each pore and their impact on global vortical flow statistics within a randomly packed porous system, (2) to scrutinize the evolution of flow kinetic energy with Reynolds number in the entire bed that appears to affect differently in the local pore-scale flow; i.e. some pores are affected by the energetic flow structures, while some pores experience lower impact from the global mean flow inertia; hence the effect on production and dissipation of energy, and (3) to investigate the trans-port and mixing characteristics of flow such as dispersion and tortuosity during the transition regime. 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 Reynolds numbers ranging from 100 to 1000 within a mono-dispersed randomly packed bed of hollow glass spheres is proposed. The approach for data analysis is based on (1) local and non-local vortex identification, (2) conventional Eulerian turbulence statistics (turbulent kinetic energy budget), proper orthogonal decomposition, and dynamic mode decomposition, and (3) Lagrangian velocity variances from Eulerian mean velocities, tortuosity, and dispersion modeling. In each case, results are presented accordingly to demonstrate the overall mixing in porous media. Finally, a road map is provided on the pore- versus macro-scale effects on the energy of flow and swirl structures, turbulence production and dissipation, as well as dispersion, and their contribution in interpreting the overall flow mixing. Also, it is demonstrated that the shear and rotational contribution of vortical structures are influenced differently from pore- versus macro-scale Reynolds numbers which interprets the scale evolution during transition process. Finally, the effect of the vortex dynamics and flow structure in randomly packed bed sphered by investigating scale, energy, and mixing characteristics.
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  • Pending Publication
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  • 2020-02-04 to 2020-09-05

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