Instability of a wake controlled by a streamwise Lorentz force is investigated through a Floquet stability analysis. The streamwise Lorentz force, which is a two-dimensional control input created by an electromagnetic...Instability of a wake controlled by a streamwise Lorentz force is investigated through a Floquet stability analysis. The streamwise Lorentz force, which is a two-dimensional control input created by an electromagnetic actuator located on the cylinder surface,adjusts the base flow to affect the three-dimensional wake instability and achieve wake stabilization and transition delay. The instability mode at a Reynolds number Re = 300 can be transformed from B to A with N = 1.0, where N is an interaction number representing the strength of the Lorentz force relative to the inertial force in the fluid. The wake flow is Floquet stable when N increases to 1.3. The spanwise perturbation wavelengths are 3.926 D and 0.822 D in the modes A and B, respectively, where D is the cylinder diameter. In addition, the oscillating amplitudes of drag and lift are reduced with the increase in the interaction number. Particle tracing is used to explore the essential physical mechanism for mode transformation. The path lines show that suppression of flow separation hinders the fluid deformation and rotation, leading to the decrease in elliptic and hyperbolic instability regions, which is the material cause of mode transformation.All of the results indicate that wake stabilization and transition delay can be achieved under open-loop active control via the streamwise Lorentz force.展开更多
Perturbation is generally considered as the flow noise,and its energy can gain transient growth in the separation bubble.The amplified perturbations may cause unstable Kelvin–Helmohltz vortices which induce the three...Perturbation is generally considered as the flow noise,and its energy can gain transient growth in the separation bubble.The amplified perturbations may cause unstable Kelvin–Helmohltz vortices which induce the three-dimensional transition.Active control of noise amplification via dielectric barrier discharge plasma actuator in the flow over a square leading-edge flat plate is numerically studied.The actuator is installed near the plate leading-edge where the separation bubble is formed.The maximum energy amplification of perturbations is positively correlated with the separation bubble scale which decreases with the increasing control parameters.As the magnitude of noise amplification is reduced,the laminar-turbulent transition is successfully suppressed.展开更多
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education(No.20133219110039)
文摘Instability of a wake controlled by a streamwise Lorentz force is investigated through a Floquet stability analysis. The streamwise Lorentz force, which is a two-dimensional control input created by an electromagnetic actuator located on the cylinder surface,adjusts the base flow to affect the three-dimensional wake instability and achieve wake stabilization and transition delay. The instability mode at a Reynolds number Re = 300 can be transformed from B to A with N = 1.0, where N is an interaction number representing the strength of the Lorentz force relative to the inertial force in the fluid. The wake flow is Floquet stable when N increases to 1.3. The spanwise perturbation wavelengths are 3.926 D and 0.822 D in the modes A and B, respectively, where D is the cylinder diameter. In addition, the oscillating amplitudes of drag and lift are reduced with the increase in the interaction number. Particle tracing is used to explore the essential physical mechanism for mode transformation. The path lines show that suppression of flow separation hinders the fluid deformation and rotation, leading to the decrease in elliptic and hyperbolic instability regions, which is the material cause of mode transformation.All of the results indicate that wake stabilization and transition delay can be achieved under open-loop active control via the streamwise Lorentz force.
基金funded by the Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20133219110039)
文摘Perturbation is generally considered as the flow noise,and its energy can gain transient growth in the separation bubble.The amplified perturbations may cause unstable Kelvin–Helmohltz vortices which induce the three-dimensional transition.Active control of noise amplification via dielectric barrier discharge plasma actuator in the flow over a square leading-edge flat plate is numerically studied.The actuator is installed near the plate leading-edge where the separation bubble is formed.The maximum energy amplification of perturbations is positively correlated with the separation bubble scale which decreases with the increasing control parameters.As the magnitude of noise amplification is reduced,the laminar-turbulent transition is successfully suppressed.
