This research examines the vortex behaviors and aerodynamic forces in dynamic stall phenomena at a transitional Reynolds number(Re=90000)using experimental and numerical approaches.Periodic sinusoidal pitching motion ...This research examines the vortex behaviors and aerodynamic forces in dynamic stall phenomena at a transitional Reynolds number(Re=90000)using experimental and numerical approaches.Periodic sinusoidal pitching motion at two different reduced frequencies is used to achieve the dynamic stall of a NACA 0012 airfoil.Several leading edge vortices form and detach in the dynamic stall stage.The flow then quickly transitions to a full separation zone in the stall stage when the angle of attack starts to decrease.There is discrepancy between the phaseaveraged and instantaneous flow field in that the small flow structures increased with angle of attack,which is a characteristic of the flow field at the transitional Reynolds number.The interaction between the streamwise vortices in the three-dimensional numerical results and the leading edge vortex are the main contribution to the turbulent flow.In addition,the leading edge vortex that supplies vortex lift is more stable at higher reduced frequency,which decreases the lift fluctuation in the dynamic stall stage.The leading edge vortex at higher reduced frequency is strong enough to stabilize the flow,even when the airfoil is in the down-stroke phase.展开更多
This paper investigates the kinematic optimization of fish-like swimming.First,an experiment was performed to detect the motion of the fish tail foil of a fish robot.Next,the kinematic swimming model was verified expe...This paper investigates the kinematic optimization of fish-like swimming.First,an experiment was performed to detect the motion of the fish tail foil of a fish robot.Next,the kinematic swimming model was verified experimentally using an image processing method.The model includes two rotational motions:caudal foil motion and foil-pitching motion.The kinematic model allows us to evaluate the influence of motion trajectory in the optimization process.To optimize the propulsive efficiency and thrust,a multi-objective genetic algorithm was employed to handle with kinematic,hydrodynamic,and propulsion models.The results show that the caudal length has a significant effect on the performance of the flapping foil in fish-like swimming,and its influence on the motion trajectory may increase the propulsive efficiency to as high as 98%in ideal conditions.The maximum thrust coefficient can also reach approximately 3 in ideal conditions.展开更多
基金supported by the National Natural Science Foundation of China (Nos.GZ 1280, 11722215 and 11721202)supported by the National Research Foundation of Korea (NRF) grant with funding from the Korean government (MSIT) (No.2011-0030013, No.2018R1A2B2007117)
文摘This research examines the vortex behaviors and aerodynamic forces in dynamic stall phenomena at a transitional Reynolds number(Re=90000)using experimental and numerical approaches.Periodic sinusoidal pitching motion at two different reduced frequencies is used to achieve the dynamic stall of a NACA 0012 airfoil.Several leading edge vortices form and detach in the dynamic stall stage.The flow then quickly transitions to a full separation zone in the stall stage when the angle of attack starts to decrease.There is discrepancy between the phaseaveraged and instantaneous flow field in that the small flow structures increased with angle of attack,which is a characteristic of the flow field at the transitional Reynolds number.The interaction between the streamwise vortices in the three-dimensional numerical results and the leading edge vortex are the main contribution to the turbulent flow.In addition,the leading edge vortex that supplies vortex lift is more stable at higher reduced frequency,which decreases the lift fluctuation in the dynamic stall stage.The leading edge vortex at higher reduced frequency is strong enough to stabilize the flow,even when the airfoil is in the down-stroke phase.
文摘This paper investigates the kinematic optimization of fish-like swimming.First,an experiment was performed to detect the motion of the fish tail foil of a fish robot.Next,the kinematic swimming model was verified experimentally using an image processing method.The model includes two rotational motions:caudal foil motion and foil-pitching motion.The kinematic model allows us to evaluate the influence of motion trajectory in the optimization process.To optimize the propulsive efficiency and thrust,a multi-objective genetic algorithm was employed to handle with kinematic,hydrodynamic,and propulsion models.The results show that the caudal length has a significant effect on the performance of the flapping foil in fish-like swimming,and its influence on the motion trajectory may increase the propulsive efficiency to as high as 98%in ideal conditions.The maximum thrust coefficient can also reach approximately 3 in ideal conditions.
