Interplay Between Shear Layer Dynamics and Cavitation in Turbulent Flows on Microfluidic Chips: A Numerical and Experimental Study
Mohammadamin Maleki
Mechatronics, PhD Dissertation, 2025
Thesis Jury
Asst. Prof. Morteza Ghorbani (Thesis Advisor),
Prof. Dr. Ali Koşar (Thesis Co-advisor),
Prof. Dr. Burç Mısırlıoğlu,
Prof. Dr. Metin Muradoğlu ,
Assoc. Prof. Melih Türkseven,
Assoc. Prof. Hüseyin Üvet
Date & Time: June 30th, 2025 – 12:00 AM
Place: FENS L061
Keywords : Cavitation, Microscale Flows, , Computational Fluid Dynamics (CFD), Backward-Facing Step (BFS), Large Eddy Simulation (LES), Compressible Multiphase Flow, Experimental Fluid Dynamics
Abstract
Cavitation, the local evaporation and re-condensation of liquids due to pressure drops, significantly impacts engineering systems, necessitating a deep understanding for reliable design. This thesis presents a comprehensive investigation into the complex interaction of compressible cavitating flows with turbulent shear layers in microscale backward-facing step (BFS) configurations. Our methodology integrates advanced computational fluid dynamics with experimental analysis. We employed a custom three-dimensional fully compressible cavitation solver within a Large Eddy Simulation (LES) framework. This solver, leveraging an all-Mach Riemann approximation-based scheme to accurately capture complex density, pressure wave dynamics, and phase change across varying Mach number regimes. We utilized both functional (WALES) and advanced mixed Subgrid-Scale (SGS) models to robustly simulate turbulence across scales. Key findings reveal that cavitation profoundly alters turbulent flow, reducing shear layer growth, delaying reattachment, and modifying Reynolds stresses and pressure fluctuations through vapor collapse. We identified dominant low-frequency modes associated with reattachment displacement and distinct vapor transport mechanisms. Furthermore, riblet-equipped surfaces control incoming turbulence: they shift Turbulence Kinetic Energy (TKE) transport, modify Reynolds stress anisotropy, and promote larger, slower coherent structures. These riblet-induced turbulent changes directly affect cavitation dynamics and characteristics. Experimentally, the study provides the first insights into shear cavitation in a microscale BFS. We observed unique microscale shedding modes influenced by vortex strength and pressure waves. This thesis advances the understanding of turbulent cavitating flows, demonstrating that comprehensive numerical and experimental approaches are essential for designing and optimizing microfluidic and energy systems./div>
