TY - GEN
T1 - Convective and absolute instabilities in reacting bluff body wakes
AU - Emerson, Benjamin
AU - Lundrigan, Julia
AU - O'Connor, Jacqueline
AU - Noble, David
AU - Lieuwen, Tim
PY - 2011
Y1 - 2011
N2 - This paper describes the variation of bluff body wake structure with flame density ratio. It is known that the bluff body flow structure at "high" and "low" flame density ratios is fundamentally different, being dominated by the convectively unstable shear layers or absolutely unstable Von Karman vortex street, respectively. This paper characterizes the aforementioned transition and shows that the bifurcation in flow behavior does not occur abruptly at some ρu/ρ b value. Rather, there exists a range of transitional density ratios at which the flow exists intermittently in both flow states, abruptly shifting back and forth between the two. The fraction of time that the flow spends in either state is a monotonic function of ρu/ρb. This behavior is to be contrasted with lower Reynolds number, laminar flow problems where the convective/absolute instability transition occurs at a well defined value of bifurcation parameter. With this distinction in mind, however, this paper also shows that local parallel stability analyses developed for laminar base wake flows can capture many of the observed flow dependencies. These results have important implications on the dynamics of high Reynolds number, vitiated flows, where typical parameter values fall into the highly intermittent flow regime characterized in this study. This suggests that such flows exhibit two co-existing dynamical states, intermittently jumping between the two.
AB - This paper describes the variation of bluff body wake structure with flame density ratio. It is known that the bluff body flow structure at "high" and "low" flame density ratios is fundamentally different, being dominated by the convectively unstable shear layers or absolutely unstable Von Karman vortex street, respectively. This paper characterizes the aforementioned transition and shows that the bifurcation in flow behavior does not occur abruptly at some ρu/ρ b value. Rather, there exists a range of transitional density ratios at which the flow exists intermittently in both flow states, abruptly shifting back and forth between the two. The fraction of time that the flow spends in either state is a monotonic function of ρu/ρb. This behavior is to be contrasted with lower Reynolds number, laminar flow problems where the convective/absolute instability transition occurs at a well defined value of bifurcation parameter. With this distinction in mind, however, this paper also shows that local parallel stability analyses developed for laminar base wake flows can capture many of the observed flow dependencies. These results have important implications on the dynamics of high Reynolds number, vitiated flows, where typical parameter values fall into the highly intermittent flow regime characterized in this study. This suggests that such flows exhibit two co-existing dynamical states, intermittently jumping between the two.
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U2 - 10.1115/GT2011-45330
DO - 10.1115/GT2011-45330
M3 - Conference contribution
AN - SCOPUS:84865529670
SN - 9780791854624
T3 - Proceedings of the ASME Turbo Expo
SP - 377
EP - 387
BT - ASME 2011 Turbo Expo
T2 - ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition, GT2011
Y2 - 6 June 2011 through 10 June 2011
ER -