Combustion oscillations in a supersonic combustor with hydrogen injection upstream of a cavity flameholder are investigated using nonlinear analysis based on experimental measurements.Time series of both flamefront an...Combustion oscillations in a supersonic combustor with hydrogen injection upstream of a cavity flameholder are investigated using nonlinear analysis based on experimental measurements.Time series of both flamefront and wall pressure are acquired,and the state space reconstruction approach is adopted to characterize the nonlinear behavior of the combustion oscillations.Three overall equivalence ratios,0.038,0.076 and 0.11,are considered.The existence of a chaotic source in the present combustion system is demonstrated.The correlation dimension and the largest Lyapunov exponent tend to become larger with the increasing equivalence ratio,indicating a more complicated and unstable combustion system.In particular,it is found that the correlation dimension for the highest equivalence ratio is much greater than those of the two lower equivalence ratios.Two possible reasons responsible for the observed nonlinear behaviors are identified.One is the shock-related instabilities and the other is the transition of combustion stabilization mode between the cavity and jet-wake stabilized mode.展开更多
The relationship between the maximum shear stress in a substrate solid and the elastic wave reflection coefficient from the interface between the substrate solid and an overlying solid half-space is investigated. Both...The relationship between the maximum shear stress in a substrate solid and the elastic wave reflection coefficient from the interface between the substrate solid and an overlying solid half-space is investigated. Both substrate and overlying solid media are assumed to be initially isotropic and stress-free. Then as the substrate is subjected to horizontal confined stresses it becomes anisotropic. It is shown that longitudinal and shear wave reflection coefficients are related to the degree of stress induced anisotropy in the substrate medium. From this relation the confined stress level and the maximum shear stress generated on the vertical planes of the substrate are estimated. Authors in their previous investigation computed plane wave reflection coefficient in a biaxially compressed solid substrate immersed in a fluid. This paper reports for the first time how the maximum shear stress in a biaxially compressed substrate medium can be measured from the plane wave reflection coefficients when the overlying medium is also a solid half-space.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.50906098,91016028)Fok Ying Tung Education Foundation(Grant No.131055)
文摘Combustion oscillations in a supersonic combustor with hydrogen injection upstream of a cavity flameholder are investigated using nonlinear analysis based on experimental measurements.Time series of both flamefront and wall pressure are acquired,and the state space reconstruction approach is adopted to characterize the nonlinear behavior of the combustion oscillations.Three overall equivalence ratios,0.038,0.076 and 0.11,are considered.The existence of a chaotic source in the present combustion system is demonstrated.The correlation dimension and the largest Lyapunov exponent tend to become larger with the increasing equivalence ratio,indicating a more complicated and unstable combustion system.In particular,it is found that the correlation dimension for the highest equivalence ratio is much greater than those of the two lower equivalence ratios.Two possible reasons responsible for the observed nonlinear behaviors are identified.One is the shock-related instabilities and the other is the transition of combustion stabilization mode between the cavity and jet-wake stabilized mode.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41474098, 11134011)by State Key Laboratory of Acoustics (Grant No. SKLA201608)
文摘The relationship between the maximum shear stress in a substrate solid and the elastic wave reflection coefficient from the interface between the substrate solid and an overlying solid half-space is investigated. Both substrate and overlying solid media are assumed to be initially isotropic and stress-free. Then as the substrate is subjected to horizontal confined stresses it becomes anisotropic. It is shown that longitudinal and shear wave reflection coefficients are related to the degree of stress induced anisotropy in the substrate medium. From this relation the confined stress level and the maximum shear stress generated on the vertical planes of the substrate are estimated. Authors in their previous investigation computed plane wave reflection coefficient in a biaxially compressed solid substrate immersed in a fluid. This paper reports for the first time how the maximum shear stress in a biaxially compressed substrate medium can be measured from the plane wave reflection coefficients when the overlying medium is also a solid half-space.
