Reddy, VK
1991
Flame Stability and Lean Blowout
Sturgess, G.J.; Sloan, D.G.; Roquemore, W.M.; Reddy, V.K.; Schouse, D.; Lesmerises, A.L.; Ballal, D.R.; Heneghan, S.P.; Vangsness, M.D. and Hedman, P.O.
10th International Society of Air Breathing Engines, Nottingham, England, September 1991. Funded by US Air Force.
A progress report is presented on a comprehensive research program aimed at improving the design and analysis capabilities for flame stability and lean blowout in the combustors of aircraft gas turbine engines. The motivation and aims of the program are reviewed, and the unusual approach adopted to address the research issues is outlined. The supporting experimental program and the test vehicles involved are described, together with some major results obtained to date. The modeling techniques that are being explored are summarized. Their potential and limitations are highlighted. Although much work remains yet to be done, the progress made thus far gives rise to reasonable optimism for achieving the program objectives.
Experimental and Theoretical Studies in a Gas-Fueled Research Combustor
Roquemore, W.M.; Reddy, V.K.; Hedman, P.O.; Post, M.E.; Chen, T.H.; Goss, L.P.; Trump, D.; Vilimpoc, V. and Sturgess, G.J.
AIAA 29th Aerospace Sciences Meeting, Reno, NV, January 1991. Funded by US Air Force.
This paper reports the results of an investigation to determine the flow and flame characteristics of a burner which has been carefully designed to "specifically reproduce recirculation patterns and lean-blow-out (LBO) processes that occur in a real gas turbine combustor." When operated in a fuel rich mode, the flame is very stable and is anchored in the jet shear layer by a pilot flame attached to the step, near the outer edge of the air supply tube. As the equilivalence ratio is reduced, the flame becomes less stable, and eventually reaches a point where the pilot flame becomes detached (lifts) from the base region, and the entire flame structure becomes stabilized downstream. Thus, there are two distinct operating modes for the combustor: a fully attached flame and a lifted flame. As the fuel equivalence ratio is further reduced, the flame becomes progressively less stable in its lifted condition, and eventually blows out. Photographs of the flame clearly illustrate the attached and lifted flame operational regimes of the combustor. However, visual observation and conventional photographic techniques are unable to quantify the precise details of the flame transition from an attached to a lifted condition. A Computational Fluid Dynamics (CFD) model with one step chemistry was used to investigate the time-averaged features of the reacting and non-reacting flow fields. The difficulties of predicting the characteristics of the attached flame with a time averaged CFD type model are discussed. Measurements, using OH emissions and gray body radiation from 14 µm diameter filaments located near the base of the flame, clearly indicate the dynamic or intermittent nature of both the attached and lifted flames. It is theorized that unburned hydrocarbon combustion products are transported into the recirculation zone by the intermittent process; and it is these products that provide the fuel needed for the flame to attach to the outer edge of the step.
Reddy, VK
1991
Flame Stability and Lean Blowout
Sturgess, G.J.; Sloan, D.G.; Roquemore, W.M.; Reddy, V.K.; Schouse, D.; Lesmerises, A.L.; Ballal, D.R.; Heneghan, S.P.; Vangsness, M.D. and Hedman, P.O.
10th International Society of Air Breathing Engines, Nottingham, England, September 1991. Funded by US Air Force.
A progress report is presented on a comprehensive research program aimed at improving the design and analysis capabilities for flame stability and lean blowout in the combustors of aircraft gas turbine engines. The motivation and aims of the program are reviewed, and the unusual approach adopted to address the research issues is outlined. The supporting experimental program and the test vehicles involved are described, together with some major results obtained to date. The modeling techniques that are being explored are summarized. Their potential and limitations are highlighted. Although much work remains yet to be done, the progress made thus far gives rise to reasonable optimism for achieving the program objectives.
Experimental and Theoretical Studies in a Gas-Fueled Research Combustor
Roquemore, W.M.; Reddy, V.K.; Hedman, P.O.; Post, M.E.; Chen, T.H.; Goss, L.P.; Trump, D.; Vilimpoc, V. and Sturgess, G.J.
AIAA 29th Aerospace Sciences Meeting, Reno, NV, January 1991. Funded by US Air Force.
This paper reports the results of an investigation to determine the flow and flame characteristics of a burner which has been carefully designed to "specifically reproduce recirculation patterns and lean-blow-out (LBO) processes that occur in a real gas turbine combustor." When operated in a fuel rich mode, the flame is very stable and is anchored in the jet shear layer by a pilot flame attached to the step, near the outer edge of the air supply tube. As the equilivalence ratio is reduced, the flame becomes less stable, and eventually reaches a point where the pilot flame becomes detached (lifts) from the base region, and the entire flame structure becomes stabilized downstream. Thus, there are two distinct operating modes for the combustor: a fully attached flame and a lifted flame. As the fuel equivalence ratio is further reduced, the flame becomes progressively less stable in its lifted condition, and eventually blows out. Photographs of the flame clearly illustrate the attached and lifted flame operational regimes of the combustor. However, visual observation and conventional photographic techniques are unable to quantify the precise details of the flame transition from an attached to a lifted condition. A Computational Fluid Dynamics (CFD) model with one step chemistry was used to investigate the time-averaged features of the reacting and non-reacting flow fields. The difficulties of predicting the characteristics of the attached flame with a time averaged CFD type model are discussed. Measurements, using OH emissions and gray body radiation from 14 µm diameter filaments located near the base of the flame, clearly indicate the dynamic or intermittent nature of both the attached and lifted flames. It is theorized that unburned hydrocarbon combustion products are transported into the recirculation zone by the intermittent process; and it is these products that provide the fuel needed for the flame to attach to the outer edge of the step.