CFD Flame Stabilization in a Model Ramjet Combustor using a Transverse.pdf
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Flame Stabilization in a Model Ramjet Combustor using a Transverse Slot Jet D. J. Forliti 1 , and K. A. Ahmed 2 The State University of New York at Buffalo, Buffalo, NY, 14260 The present study is motivated by the desire to provide a flame stabilization environment without the use of a sudden expansion or bluff body that incurs a thrust penalty. A transverse slot jet issuing into a confined cross flow is used to produce a low-speed recirculation zone similar to that formed downstream of a rearward-facing step, a configuration often employed for flame holding. The study of the nonreacting flowfield characteristics of the induced recirculation is conducted to identify parametric aspects of the recirculation zone and study the effects of placing a diffuser upstream of the test section. For combustion conditions, the flame stabilization limits are documented. Altering the equivalence ratio of the transverse jet relative to that of the main flow allows for secondary control of the stabilization limits. Flowfield characteristics for a representative combustion case are presented. Combustion tends to enhance shear and create higher turbulence levels. Intense heat release rates occur downstream of the recirculation zone. I. Introduction T HE stabilization of a premixed flame in a high-speed internal environment received a considerable amount of interest from many researchers. e.g. 1-3 Flame stabilization behind a bluff body represents the most common strategy for flame anchoring. 4-12 Bluff bodies and rearward-facing step flows stabilize the flame by introducing a low- velocity recirculation zone containing combustion products that act as a continuous ignition source. Flame holding using a bluff body plays an important role in the performance of ramjets, scramjets, and afterburners for turbojet and turbofans. 13 Although these devices provide an environment suitable for flame holding, a drag penalty is incurred. An alternative fluidic-based approach using a transverse slot jet would reduce the thrust penalties associated with the sudden expansion/bluff body geometry while producing a flowfield with flame holding potential. The transverse jet, or jet in cross flow, is a flow that is relevant to many applications. The most common applications include V/STOL aircraft in transition flight, film cooling of turbine blades, dilution zones in gas turbine combustors, and reaction control jets for rockets and missiles. Many previous efforts focused on the detailed flowfield features, jet trajectory behavior, and scaling properties of round jets issuing into unconfined cross flow. 14-24 Geometry variations that were previously explored include jet nozzle shape, number of jets, angle of the jet, and spanwise/transver se confinement. 1 Assistant Professor, Department of Mechanical and Aerospace Engineering, 326 Jarvis Hall, AIAA member. 2 Research Assistant, Department of Mechanical and Aerospace Engineering, 311 Jarvis Hall, AIAA student member. 46th AIAA Aerospace Sciences Meeting and Exhibit 7 - 10 January 2008, Reno, Nevada AIAA 2008-104 Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
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