| The control of flow separation of NACA0012 airfoil with synthetic jet at Reynolds number Re=1×104 is numerically simulated by computational fluid dynamics(CFD).The characteristics of the vortex shedding causing the flow separation of the airfoil are studied in detail,and the influence of the blowing vortex of the synthetic jet on the vortex structure of the flow field around the airfoil is explained.It is of great significance for deeply understanding the evolution law of vortex structure in airfoil flow field and using active control to suppress flow separation.The variation of shedding vortex structure at different angles of attack and evolution law of shedding vortex near airfoil flow field rom 0°?24° is studied at ?=5°,?=10°,?=14°,?=16°,?=19° and ?=22°.Using spectrum analysis,the frequency characteristics of shedding vortex corresponding to the above five angles of attack are quantitatively studied,the characteristic frequency and frequency amplitude of spectrum curve are concerned,and the relationship between the corresponding trailing edge shedding vortex frequency and the variation trend of airfoil lift and drag coefficient is analyzed.The Strouhal number is introduced to illustrate the flow stability corresponding to different flow patterns.The results show that with the increase of the attack angle of the airfoil,the flow state of the flow field will change from steady state to unsteady state.In the periodic wake vortex shedding flow field,according to the structure and frequency of the shedding vortex,when the airfoil angle of attack ?>7°,the shedding vortex will show 2S(single)mode-chaotic state-2S(single)mode-quasi periodic flow with the increase of angle of attack.There is a corresponding relationship between the fluctuation law of shedding vortex and the fluctuation law of spectrum curve.With the increase of the angle of attack,the Strouhal number corresponding to the shedding vortex frequency basically shows a decreasing trend.The Strouhal number in different flow field states is sorted from high to bottom as 2S(single)mode>quasi periodic flow>chaotic state.Using synthetic jet control technology,the influence of the vortex blown out by different frequencies on the vortex structure of the flow field around the airfoil and the corresponding frequency spectrum characteristics of the shedding vortex.The synthetic j et actuator is installed in front of the flow separation point at each angle of attack,where,at ?=10°,?=14°,?=16°,the installation position of jet actuator is 7.6%chord length.At ?=19°,?=22°,the installation position of j et actuator is 1%chord length.The blowing direction of the jet is along the tangential direction of the airfoil,in which the jet direction is 12° at 7.6%chord length and 30° at 1%chord length.Under the excitation of synthetic jet,the structure of vortex shedding in airfoil flow field changes accordingly.It is found that the jet will stabilize the flow field in 2S(Single)mode at most angles of attack and in chaos at a small angle of attack.At the same time,the jet will delay the angle of attack of the chaotic state,and the lift drag coefficient and the corresponding spectrum characteristics are more orderly than those without excitation.The effects of single excitation frequency and combined excitation frequency on the action effect of synthetic jet are compared.The results show that the two excitation methods have the same effect on lifting force.The combined excitation frequency can make the fluctuation of lift curve more orderly,and the corresponding airfoil flow field state is closer to 2S(Single)mode.The flow field is stable in chaos at a small angle of attack.The effects of single excitation frequency and combined excitation frequency on the action effect of synthetic jet are compared and studied.The results show that the two excitation methods have the same effect on lifting force.The combined excitation frequency can make the fluctuation of lift curve more orderly,and the corresponding airfoil flow field state is closer to 2S(Single)mode. |
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