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Askar Kazbekov
(Advisor: Prof. Steinberg)
will propose a doctoral thesis entitled,
Flame-Scale Turbulence Production and Inter-Scale Energy Transfer in Premixed Combustion.
On
Wednesday, March 10 at 3:00 p.m.
Ben T. Zinn Combustion Laboratory, Conference Room
https://bluejeans.com/8795004325/
Abstract
Turbulent premixed combustion is widely used for energy conversion in power generation and propulsion devices. However, our understanding of the underlying fluid dynamics, combustion, and their interaction is still incomplete. The complexity of turbulent combustion arises from the non-linear, multi-scale, and multi-physics nature of the problem, which involves interactions between fluid dynamic and chemical processes across a myriad of length and time scales. The existing literature demonstrates that the dynamics of reacting turbulence does not necessarily follow the same phenomenology as in non-reacting incompressible turbulence. One of the key differences is the production of turbulence at the scales of the flame, which has the potential to reverse the classical turbulent energy cascade in a process termed as ‘backscatter’. Moreover, flame-scale turbulence production and backscatter were shown to potentially depend on the magnitude of the pressure gradients across the flame; this is reflected in barcolinic torque enstrophy production and sub-filter-scale pressure-work. Previous studies have predominantly focused on flames in homogeneous isotropic turbulence (HIT), in which the pressure gradients are associated with the flame and turbulence themselves. In contrast, practical combustors exhibit mean pressure fields, generated by the flow, which can induce significantly different turbulence dynamics as compared to non-reacting turbulence. The proposed research explores the conditions at which significant flame-induced turbulence production and energy backscatter occur in an aerospace relevant configuration, and attempts to identify the underlying physical mechanisms that have a leading order impact on these processes. This is done through systematic variation of the global equivalence ratio, turbulence intensity, and the magnitude of the mean pressure field. The impact of these controlling parameters on turbulence production and energy backscatter is assessed through the analysis of enstrophy and filtered kinetic energy transport equations. Tomographic particle image velocimetry (TPIV) and planar laser induced fluorescence (PLIF) are used to measure the 3D velocity fields and planar distribution of formaldehyde, respectively; the relevant thermodynamic properties (e.g. density and progress variable) are estimated from PLIF data. Ultimately, this work will provide a rigorous assessment of the extent to which current turbulence modeling paradigms hold in aerospace relevant combustion, as well as the data necessary to develop and validate new models if required.
Committee
