Student Name: Guru Charan Ganesh

Advisor: Dr. Timothy Lieuwen

Milestone: PhD Thesis Proposal

Degree Program: Aerospace Engineering

Title: Unsteady Wake Structures in Jets in Crossflow

Abstract: The jet in crossflow (JICF) is a fundamental, fluid mechanics-rich flow topology employed in various combustor architectures such as lean premixed combustors, staged combustors, as well as in film cooling technologies, owing to its excellent mixing properties. While on paper the implementation of this flow configuration is simple enough, the interaction between the two fluid streams results in a super three-dimensional, unsteady large scale vortical structures, namely: horseshoe vortices, shear layer vortices, counter-rotating vortex pairs, and the wake vortices. Out of these, the wake vortices are the least understood and have received limited attention. A large body of literature exists in characterizing the formation and development of the shear layer vortices (SLV) and the counter-rotating vortex pairs (CVP), and as such, control strategies are developed around their behavior in system level applications. Despite the bulk of the mixing is attributed to the SLVs and the CVP, the wake structures appear to add another layer of far field mixing from their tornado-like behavior and are the major focus of this work. Although experimental and computational studies have been performed to characterize the periodicity associated with the wake vortices, general consensus on their precise formation mechanism and source of vorticity is yet to be achieved. Moreover, despite the existence of tornado-like structures in the wake of the jet are widely acknowledged in the research community, the exact nature of their evolution is yet to be explained. In the context of a reacting jet in crossflow (staged combustors, for instance), presence of combustion has been shown to significantly alter the underlying hydrodynamics of the flow field due to additional physics like dilatation effects, baroclinic torque, and local viscosity changes, resulting in complex flame-flow interactions. Furthermore, combustor phenomena such as flame stabilization and Nox emissions have been shown to be highly sensitive to the background fluid mechanics of this flow field, necessitating a systematic investigation onto combustion effects. Additionally, since the evolution of these large scale flow structures occurs at their respective time and length scales, studies on their interactions require highly-resolved spatial and temporal datasets. Motivated by the above-mentioned gaps in literature and challenges on analysis, this proposal seeks to explore the characteristics of the wake structures and attempts to answer fundamental questions like: (1) What is the nature of flow separation mechanisms (low pressure-driven events vs CVP induction) and source of vorticity (crossflow boundary layer vs jet shear layer), (2) what is the effect of flame attachment location and the consequent local heat release distribution on wake vortices, (3) what are the unsteady features of the wake vortices (characteristic frequencies, symmetry, mode shapes) and how do they compare between non-reacting and reacting jet in crossflow datasets. These research questions are systematically investigated using high fidelity large eddy simulations. The computations will be performed over a range of fluid dynamic parameters characterizing the flow field and the dependencies of the topological features of wake structures on test parameters will be ascertained. 

Date and time: 2026-05-01, 9.00 AM - 11.00 AM

Location: MK-317

Committee:
Dr. Timothy Lieuwen (advisor), School of Aerospace Engineering
Dr. Ari Glezer, School of Mechanical Engineering
Dr. Joseph Oefelein, School of Aerospace Engineering
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