The characterization of breakup mechanisms in a Liquid jet in Crossflow (LJIC) is of great importance to the propulsion industry. The current study focuses on analyzing and understanding these breakup mechanisms as it pertains to the operability conditions of airbreathing engines. These breakup mechanisms are studied by extracting and identifying spatial patterns and temporal dynamics of their coherent structures that define different modes of a breakup. These coherent structures associated to transverse jets are highly intermittent and cannot be classified by traditional global modal techniques. The primary objective of this study was to identify intermittent coherent structures associated with the four primary column breakup regimes: enhanced capillary breakup, bag breakup, multimode breakup, and shear breakup. The approach used in this study utilizes Proper orthogonal decomposition in conjunction with a novel technique known as the Multi-Resolution Dynamic Mode Decomposition (MrDMD). The applied methodology identifies coherent structures of the liquid surface and is an extension of the currently used Dynamic Mode Decomposition (DMD). The key benefit of MrDMD is it parses nonlinear dynamical systems into multi-resolution time-scaled components to capture intermittent mechanisms. The current methodology to extract MrDMD modes relies purely based on amplitude inspection. However, amplitude inspection becomes redundant for time-resolved snapshots of a highly turbulent system and is therefore not sustainable. In this study, a new method of modal extraction is utilized, this methodology is centered around using the repetition of frequency as detection for relevant modes rather than the magnitude of amplitude. This method will be referred to as Robust MrDMD. Robust MrDMD is applied to time-resolved series of column region snapshots for the four spray regimes. Relative frequencies of each breakup regime are extracted and identified. The frequencies for the characterized fuel jet injection dynamics are linked to critical non-dimensional parameters known as Strouhal number. The results produced a viable new breakup regime map associated with the strouhal number and weber number and its momentum flux ratio. Results conclusively show that all the breakup regimes contain a coherent structure associated with St=0.06-0.08, which dictates ligament breakup. It is also shown that coherent structures associated with small scale shear breakup of St 025-0.28 are shared between all the multimodal the shear breakup cases. These coherent structures are classified with an approximate time scale and found to correlate with a specified Strouhal number directly.


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Graduation Date





Ahmed, Kareem


Master of Science in Aerospace Engineering (M.S.A.E.)


College of Engineering and Computer Science


Mechanical and Aerospace Engineering

Degree Program

Aerospace Engineering; Thermofluid Aerodynamic Systems




CFE0008229; DP0023583





Release Date

August 2025

Length of Campus-only Access

5 years

Access Status

Masters Thesis (Campus-only Access)

Restricted to the UCF community until August 2025; it will then be open access.