ORCID

0000-0001-8172-8076

Keywords

turbulence, fluid dynamics, hydrodynamic stability, elliptical instability, combustion, turbulent flame

Abstract

The conveyance of energy through the formation, interaction, and destruction of eddies over a wide range of spatial scales, from the largest scale where energy is injected to the smallest scales where the energy is dissipated through viscosity remains one of the most fundamental unsolved problems in fluid mechanics. This dissertation provides a comprehensive investigation spanning multiple flow regimes consisting of high-speed reacting flows and transitional boundary layer turbulence to establish the necessary conditions for turbulent flows to sustain cascades of energy to arbitrarily small scales while demonstrating how the nonlinear development of the elliptical instability leads to the emergence of turbulence. It shows that an instantaneous acceleration of the traditional Kolmogorov cascade can occur if the critical threshold between strain and rotation is exceeded in the final stages of the turbulent instability cascade.

The investigations revealed that within strain-dominated regions, the local cascade deviates from the canonical -5/3 inertial range scaling. The dominance of stretching over viscous dissipation in these localized zones enables vortex breakdown and provides the burst of energy transfer necessary to complete the transition to turbulence. The elliptical instability, creating spatially intermittent regions where accelerated energy transfer occurs through enhanced vortex stretching through intermediate scales, explains the long-standing paradox of why observed transition rates exceed primary instability predictions. The viscous term, while subdominant during the instability evolution, ultimately determines the dissipation scale once the coherent structures have been destroyed through the strain- and stretching-dominated breakdown process.

Completion Date

2025

Semester

Fall

Committee Chair

Ahmed, Kareem

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Department of Mechanical and Aerospace Engineering

Format

PDF

Identifier

DP0029832

Document Type

Thesis

Campus Location

Orlando (Main) Campus

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