Numerical Simulations of Flowfields in a Central-Dump Ramjet Combustor. 3. Effects of Chemistry PDF Download
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Author: Kazhikathra Kailasanath
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Languages : en
Pages : 52
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This report is the third in a series which presents the results of numerical simulations performed to isolate and study acoustic-vortex-chemical interactions in an idealized ramjet consisting of an axisymmetric inlet and combustor and a choked nozzle. Both reactive and nonreactive flows have been simulated. The nonreactive flow calculations show complex interactions among the natural instability frequency of the shear layer at the inlet-combustor junction and the acoustics of both the inlet and the combustor. The entire flow oscillates at a low frequency which corresponds to that of a quarter-mode in the inlet. For the reactive flow cases studied, energy release alters the flow field substantially. Energy release in a large vortex is in phase with the pressure oscillation over a substantial region of the combustor and results in the observed amplification of the low-frequency oscillations and leads to combustion instability. The large pressure oscillation also modifies the vortex shedding process. Keywords: Ramjet, Turbulence, Combustion instability. (jes).
Author: Kazhikathra Kailasanath
Publisher:
ISBN:
Category :
Languages : en
Pages : 52
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Book Description
This report is the third in a series which presents the results of numerical simulations performed to isolate and study acoustic-vortex-chemical interactions in an idealized ramjet consisting of an axisymmetric inlet and combustor and a choked nozzle. Both reactive and nonreactive flows have been simulated. The nonreactive flow calculations show complex interactions among the natural instability frequency of the shear layer at the inlet-combustor junction and the acoustics of both the inlet and the combustor. The entire flow oscillates at a low frequency which corresponds to that of a quarter-mode in the inlet. For the reactive flow cases studied, energy release alters the flow field substantially. Energy release in a large vortex is in phase with the pressure oscillation over a substantial region of the combustor and results in the observed amplification of the low-frequency oscillations and leads to combustion instability. The large pressure oscillation also modifies the vortex shedding process. Keywords: Ramjet, Turbulence, Combustion instability. (jes).
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Category :
Languages : en
Pages : 35
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This paper presents results of numerical simulations of the cold flow in a central dump ramjet combustor. Tests of the boundary conditions and numerical resolutions are used to perform the simulations. The simulations are used to isolate and study the interaction between acoustic waves and large scale vortex structures. A strong coupling between the acoustic modes of the chamber and large scale vortex structures is observed. The results in the early part of the calculations indicate unforced natural vortex growth near the entrance to the combustor (dump plane) at a frequency close to that of the first longitudinal acoustic mode. With time, the acoustic modes shift the frequency of the most amplified vortex rollup mode near the dump plane into resonance with the acoustic mode. The simulations indicate that the location in space where the modes grow can also be shifted by acoustic forcing. An interesting feature observed in the simulations is a low frequency mode corresponding to the arrival of the merged vortex structures at the choked exit. This mode causes major changes in the merging pattern of the vortices.
Author: K. Kailasanath
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Category :
Languages : en
Pages : 39
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A potentially important source of large pressure oscillations in compact ramjets is a combustion instability induced by the interaction of large-scale vortex structures with the acoustic modes of the ramjet. To study these interactions, we have performed time-dependent, compressible numerical simulations of the flow field in an idealized ramjet consisting of an axisymmetric inlet and a combustor. The simulations indicate strong coupling between the flow field and the acoustics of both the inlet and the combustor. For the cases studied, forcing at the first longitudinal acoustic mode of the combustor induces vortex-rollup near the entrance to the combustor at that frequency. A low frequency oscillation is also observed in all the simulations. Pressure and velocity fluctuations in the inlet indicate that the low frequency corresponds to a quarter-wave mode in the inlet. Changing the length of the inlet appropriately changes the observed low frequency. The merging pattern of the inlet is changed. These merging patterns are explained on the basis of an interaction between the vortex-rollup frequency and the acoustic modes of the inlet and combustor. Keywords: Ramjet, Combustion instability, Turbulence. (mjm).
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Category : Aeronautics
Languages : en
Pages : 704
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Category : Government publications
Languages : en
Pages : 1316
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Author: American Society of Mechanical Engineers. Winter Annual Meeting
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Category : Science
Languages : en
Pages : 146
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Category : Aeronautics
Languages : en
Pages : 568
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A selection of annotated references to unclassified reports and journal articles that were introduced into the NASA scientific and technical information system and announced in Scientific and technical aerospace reports (STAR) and International aerospace abstracts (IAA).
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Category :
Languages : en
Pages : 566
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Author:
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Category : Aeronautics
Languages : en
Pages : 580
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Author: Combustion Institute (U.S.) Eastern States Section. Fall Technical Meeting
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Category : Combustion
Languages : en
Pages : 496
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