![]() ![]() The dynamic stall of three-dimensional rotors and two-dimensional airfoils is investigated which indicates that the dynamic stall has a great influence on their aerodynamic performance. The retreating blades of the rotor generally work in an aerodynamic environment with a large angle of attack (AoA), and the complex unsteady dynamic stall phenomenon caused by the AoA of most sections of the blade exceeds its stall AoA. The limitation of the forward flight speed of helicopters is closely related to the flow characteristics of the airflow on the rotor blade surface. However, the low flight speed of conventional helicopters greatly limits their application range. IntroductionĪs compared with a fixed-wing aircraft, helicopters have unique advantages, such as vertical take-off and landing, high maneuverability, and hovering in the air, and they are widely used in both military and civilian fields. Moreover, the position of the injection slot is found to have a greater effect on the dynamic stall suppression, while the size of the injection slot and the position and size of the suction slot have little effect. It is found that there is a jet momentum coefficient that optimizes the suppression effect of the dynamic stall of the rotor airfoil. On this basis, the control parameters of the CFJ are further studied, including the influences of the jet momentum coefficient and the positions and sizes of the injection and suction slots on suppressing the dynamic stall of the rotor airfoil. ![]() The diffusion and blending of the turbulent shear layer between the CFJ injection jet and the main flow excite the main flow and enhance its ability to resist the reverse pressure gradient this suppresses the generation and development of the separation vortex, thereby enhancing the aerodynamic characteristics, improving the hysteresis effect, and increasing the system stability. Via the study of the typical conditions of CFJ control to suppress the dynamic stall of the OA212 rotor airfoil, it is verified that this method has a good effect on dynamic stall suppression. The numerical methods are validated by a NACA0012 pitching airfoil case and a NACA6415 airfoil case based on the CFJ, and good agreement with experiments is found. The effect of the CFJ on the unsteady dynamic stall characteristics of the rotor airfoil is numerically investigated via numerical simulations of the unsteady Reynolds-averaged Navier-Stokes (URANS) equations coupled with the Spalart-Allmaras (S-A) turbulence model. The flow field is dominated not by the physical airfoil, but rather by the effective body encompassing both the physical airfoil and its trailing wake.Ĭontinual Analysis of the Relationship Between Stall Hysteresis and Circulation ParameterIn this study, a dynamic stall control strategy, called the co-flow jet (CFJ), is applied to the rotor airfoil. This variance in circulation parameter has associated stall-circulation parameters for each state (attached vs stalled), and it, therefore, necessary to reduce the angle of attack, or the circulation parameter, below that of the effective body (stalled flow field). It is proposed that stalled airfoils have a significantly different circulation parameter than that of the attached states for the same airfoil. The present work, as an extension of Morris 2009 and Morris and Rusak 2013, suggests that the flow state around a 2D airfoil is dominated by the circulation parameter, which includes airfoil geometry, angle of attack, and Reynolds number effects. Stall hysteresis is a well-documented phenomenon that has been shown to affect all aircraft and turbo-machinery (wind turbines, jet engines, etc.) This hysteresis poses a problem for aircraft control in the event of a stall, where the lift produced by the wing becomes dependent on the history of its AOA. Stall hysteresis is the phenomenon where an airfoil produces less lift than expected for a given angle of attack as recovery from stall is attempted. The bursting of the bubble coincides with the onset of stall. This causes the laminar flow to massively separate from the upper surface. As an airfoil’s AOA is increased, a small separation bubble forms on the upper surface, and grows until it bursts.
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