Marios C. Soteriou

The influence of temperature ratio on the dynamics of bluff body stabilized flames

The dynamics of bluff body stabilized flames are investigated using an unsteady, Lagrangian simulation technique . This paper presents an analysis of results from a parametric study of temperature ratio across a flame stabilized on a bluff body confined in a duct . The simulation presented in this study is a two -dimensional description of a premixed inflow of reactants with flame sheets attached to a triangular wedge. The analysis concentrates on flow field dynamics related to the transition from the asym metric Von Karman shedding found in non -reacting bluff body flows to independent shear layer vorticity commonly observed in many reacting flows. Details of this transition are described in terms of the instantaneous vorticity field, as well as mean and uns teady components of velocity and temperature. It is shown that for relatively small temperature differences across the flamesheets, the Von Karman shedding mode remains dominant, although the strength of the shed vortices decreases with increasing temperat ure ratio. As the temperature ratio increases, the Von Karman shedding mode is completely suppressed, and this suppression is clearly evident through RMS temperature profiles as well as turbulent stresses near the bluff body.

Fuel control of a ducted bluffbody flame

In this paper, we consider the problem of controlling the flame dynamics of a ducted, premixed, bluffbody flameholder stabilized flame. The flame dynamics arise due to (complicated) interaction between the fluid dynamics and the inherent kinematical flame motion. For control oriented flame modelling, we make the simplifying assumption of ignoring the vortical component of the fluid dynamics in the problem, but retain the effects due to burning and fuel actuation. The resulting reduced order model arises as a hyperbolic pde with a delay that depends upon the state. We use the reduced order model to define and study a fuel actuation based control problem of tracking the heat released due to flame motion against a prescribed reference signal. We validate the results of control using a detailed simulation of the physical problem.

Impact of convection and diffusion processes in fundamental limitations of combustion control

This paper is aimed at understanding the role of physical processes of convection and diusion on the fundamental limitations arising in fuel control of thermoacoustic instabilities. For this purpose, we develop a physics based reduced order heat release model that is analytical and incorporates a) distributed ame dynamics, b) exothermicity related dilatation eects, and c) distributed fuel dynamics including diusion. Results show that convection leads to the presence of distributed delay, while diusion, depending upon diffusivity and exothermicity constants, may lead to the presence of right half plane zeroes in the response of heat release to the fuel control command. We isolate these non-minimum phase aspects of dynamics and apply the theory of fundamental limitations to obtain conclusions on the impact of convection and diusion on ones ability to use fuel based feedback control in controlling heat release.