In the first chapter of the study, wavelet multiresolution analysis (WMRA) is extended to describe inter-phase, cross-scale interactions involving turbulence kinetic energy (TKE) of particle-laden turbulence. Homogeneous isotropic turbulence suspended with inertial particles at the Stokes number of unity is analyzed. Effects of the two-way coupling on spectral TKE transfer are examined. Particle concentration alone does not indicate a definite direction of inter-phase energy transfer. Rather, particle clusters behave as an energy source or sink with similar probabilities. In addition, the joint statistics show thequalitative consistency of the subgrid-scale (SGS) Stokes number in describing the two-way interactions, which should be considered in the SGS modeling of two-way coupled particle-laden turbulence. In the second chapter, direct numerical simulation (DNS) of viscoelastic turbulent channel flow is conducted and the resulting velocity field is analyzed using the WMRA to identify the drag reduction mechanism by polymer additives. At the friction Reynolds number Re? = 145 and the Weissenberg number Wi = 40, the DNS of a viscoelastic channel flow is performed using the finitely extensible nonlinear elastic model. In-plane WMRA is performed to investigate the modulation of TKE due to interactions between polymer solution and turbulence across different scales. A formulation is proposed to evaluate the effects of polymers on the spectral TKE transfer. Using joint probability analysis, it has been shown that polymers absorb TKE from the near-wall region and store it as elastic energy at ?+ ≲ 20, while they enhance TKE in the log layer. Ultimately, this study introduces a framework for optimizing large-eddy simulation (LES) models via WMRA. By employing the spectrally and spatially localized decomposition of wavelets, an optimal balance between resolved inter-scale energy transfer and modeled SGS dissipation is enforced across a range of nominal LES grid widths. This formulation either determines a constant for the SGS model or offers an analytical expression for SGS closure that maximizes spectral energy transfer between resolved and unresolved scales at a specific cutoff scale. This proposed approach is assessed in the context of incompressible HIT. The constant of the one-parameter Smagorinsky closure model is optimized to align with the theoretical predictions.

Cavitation bubbles in the human body, when subjected to rapid mechanical load, are being increasingly considered as a possible brain injury mechanism during contact sports and military operations. Due to this great importance, it is essential to fundamentally understand the cavitation bubble dynamics in varying biological systems. In this dissertation, experimental and theoretical characterization of cavitation dynamics in soft matters from tissue simulant soft gels (e.g., agar, agarose, and gelatin) to actual live cells are performed.First, cavitation nucleation and bubble growth in different types of tissue simulants are studied under translation impact. The critical acceleration that corresponds to onset of cavitation bubble burst is measured in the soft gels and individual gel types indicate significantly different trends in the critical acceleration and bubble shape (e.g., A gel-specific sphere-to-saucer transition) with increasing gel stiffness. Possible underlying mechanisms of the experimental observations are provided in the concepts of a damaged zone and crack propagation. This study sheds light on potential links between traumatic brain injuries and cavitation bubbles induced by translational acceleration, the overlooked mechanism in the literature. Second, a drop-tower-based repetitive impact tester is newly designed to mimic biological systems under a wide range of impact conditions including high strain rate as well as repeated loadings. Theoretical approach based on a two-degree-of-freedom mass-spring-damper model simulates the transient dynamic response of the system with experimental validations. As one of main implications, a novel noncontact detecting method is developed to capture initial cavitation nucleation during successive drop events. This study also observes impact characteristics dependent cavitation bubble responses, which have not been characterized by other methods (e.g., laser or ultrasound induced cavitation rheology). Finally, although significant efforts have been made in the dynamic response of tissue simulants, there is a huge knowledge gap between the soft gels and actual live cells due to the lack of the experimental capability and of knowledge for complicated cell responses. Newly designed in vitro experimental setup and systematic characterization of specific cell types, i.e., Hs27 fibroblasts, enable a testing of spatio-temporal responses of cells under mechanical impact by controlling their static and dynamic behaviors.

Sydney University has developed a variant of the well-known Sydney/Sydnie piloted jet burner. The introduction of this new burner is for a purpose referred to as airblast atomization. This variant comprises a retractable needle that can be translated within the co-flowing airstream. The performance of the computational simulation is based on a high-pressure turbulent jet having three different recess lengths considering acetone as the fuel. The computational analysis is performed using the primary atomization process in which the bulk amount of liquid transitions into tiny droplets. In the Volume-of-Fluid (VOF) model, the velocity field and pressure field are used to get the atomization locations. The quadratic formula is applied to atomization locations to calculate the mean drop size (Sauter Mean Diameter). The droplets are injected from the atomization locations and tracked considering as the point particles. The steady-state Sauter mean diameter particles are computed using the User Define Memory (UDM) code. The velocity field, droplet size (Sauter mean diameter), and droplet trajectory are compared with the experimental data for the validation protocol.