In order to increase the accuracy of turbulence field reconstruction,this paper combines experimental observation and numerical simulation to develop and establish a data assimilation framework,and apply it to the stu...In order to increase the accuracy of turbulence field reconstruction,this paper combines experimental observation and numerical simulation to develop and establish a data assimilation framework,and apply it to the study of S809 low-speed and high-angle airfoil flow.The method is based on the ensemble transform Kalman filter(ETKF)algorithm,which improves the disturbance strategy of the ensemble members and enhances the richness of the initial members by screening high flow field sensitivity constants,increasing the constant disturbance dimensions and designing a fine disturbance interval.The results show that the pressure distribution on the airfoil surface after assimilation is closer to the experimental value than that of the standard Spalart-Allmaras(S-A)model.The separated vortex estimated by filtering is fuller,and the eddy viscosity field information is more abundant,which is physically consistent with the observation information.Therefore,the data assimilation method based on the improved ensemble strategy can more accurately and effectively describe complex turbulence phenomena.展开更多
The computational fluid dynamics method was used to simulate the flow field around a wind turbine at the yaw angles of 0°,15°,30°,and 45°.The angle of attack and the relative velocity of the spanwi...The computational fluid dynamics method was used to simulate the flow field around a wind turbine at the yaw angles of 0°,15°,30°,and 45°.The angle of attack and the relative velocity of the spanwise sections of the blade were extracted with the reference points method.By analyzing the pressure distribution and the flow characteristics of the blade surface,the flow mechanism of the blade surface in the yawed condition was discussed.The results showed that the variations of the angle of attack and the relative velocity were related to the azimuth angle and the radius in the yawed condition.The larger the yaw angle was,the larger the variation was.The pressure distribution in the spanwise sections was affected by both the angle of attack and the relative velocity.The angle of attack was more influential than the relative velocity.At the same yaw angle,when the angle of attack decreased,the c_(p)∼x/c curve shrunk inward and the lift force decreased.The larger the yaw angle was,the more obvious the shrink was.The effect of the yaw on the blade root region was higher than its effect on the blade tip region.展开更多
Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study f...Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.展开更多
During the initial stage of vertical launch,a missile may exhibit an uncertain roll angle(φ)and a high angle of attack(α).This study focuses on examining the impact of roll angle variations on the flow field and the...During the initial stage of vertical launch,a missile may exhibit an uncertain roll angle(φ)and a high angle of attack(α).This study focuses on examining the impact of roll angle variations on the flow field and the unsteady aerodynamics of a canard-configured missile atα=75°.Simulations were performed using the validated k-ωSST turbulence model.The analysis encompasses the temporal development of vortices,the oscillatory characteristics of the lateral force,and the fluctuation of kinetic energy distribution within the framework of proper orthogonal decomposition(POD).The results indicate that the flow field surrounding the canardconfigured missile is characterized by inconsistent shedding cycles of Kármán-like and canard-separated vortices.A distinct transition zone is identified between these vortices,where vortex tearing and reconnection phenomena occur.With increasing roll angles from 0°to 45°,there is an observed shift in the dominant frequency of the lateral force from the higher frequency associated with Kármán-like vortex shedding to the lower frequency of canard vortex shedding.The shedding frequency of Kármán-like vortices corresponds to the harmonics of the canard vortex shedding frequency,indicative of a higher-order harmonic resonance.The frequency of the lateral force is observed to decrease with an increase in roll angle,except in configurations lacking distinct canard-separated vortices,which are characterized by a“+”shape.The POD analysis reveals that the majority of the fluctuation energy is concentrated in the oscillations and shedding of the canard-separated vortices,leading to pressure fluctuations that are primarily observed on the canard and the downstream region of the canard.展开更多
A numerical model has been developed for computing turbulent flow in plane-wall diffuser.The model solves the weakly compressible flow equations with the application of the Smagorinsky's subgrid-scale turbulence m...A numerical model has been developed for computing turbulent flow in plane-wall diffuser.The model solves the weakly compressible flow equations with the application of the Smagorinsky's subgrid-scale turbulence model and the boundary conditions of partial slip and no slip at the solid wall.Application examples include two-dimensional calculations of unstalled and stalled flows in diffusers of small diverging angle,as well as transitory stall flow in a symmetric diffuser of 16°total angle.For the unstalled and stalled flows,the calculated pressure recovery and velocity profile are compared with experimental data.For the transitory stall flow,the com- putational result shows the unsteady flow features including the vortex shedding and stall washout phenomena that have been experimentally observed.展开更多
This paper presents the experimental investigations of high angle-of-attack flow con-trol on NACA0012 airfoil using vortex-generating devices in low speed wind tunnel. The vortex-generating devices used are (i) top-su...This paper presents the experimental investigations of high angle-of-attack flow con-trol on NACA0012 airfoil using vortex-generating devices in low speed wind tunnel. The vortex-generating devices used are (i) top-surface triangular wing type vortex-generators,(n) leading-edge vortex-generators, (iii) leading-edge slots. Experiment Renolds number range is 4.9×105 to 6.5×105, the angle-of-attack range is -10° to 20°. The comparisons of experimental results show that the vortex-generating devices can dramatically improve airfoil aerodynamic characteristics at normal stall angle-of-attack by increasing both the lift and the lift-to-drag ratio.展开更多
基金Project supported by the Foundation of National Key Laboratory of Science and Technology on Aerodynamic Design and Research of China(No.614220119040101)the National Natural Science Foundation of China(No.91852115)。
文摘In order to increase the accuracy of turbulence field reconstruction,this paper combines experimental observation and numerical simulation to develop and establish a data assimilation framework,and apply it to the study of S809 low-speed and high-angle airfoil flow.The method is based on the ensemble transform Kalman filter(ETKF)algorithm,which improves the disturbance strategy of the ensemble members and enhances the richness of the initial members by screening high flow field sensitivity constants,increasing the constant disturbance dimensions and designing a fine disturbance interval.The results show that the pressure distribution on the airfoil surface after assimilation is closer to the experimental value than that of the standard Spalart-Allmaras(S-A)model.The separated vortex estimated by filtering is fuller,and the eddy viscosity field information is more abundant,which is physically consistent with the observation information.Therefore,the data assimilation method based on the improved ensemble strategy can more accurately and effectively describe complex turbulence phenomena.
文摘The computational fluid dynamics method was used to simulate the flow field around a wind turbine at the yaw angles of 0°,15°,30°,and 45°.The angle of attack and the relative velocity of the spanwise sections of the blade were extracted with the reference points method.By analyzing the pressure distribution and the flow characteristics of the blade surface,the flow mechanism of the blade surface in the yawed condition was discussed.The results showed that the variations of the angle of attack and the relative velocity were related to the azimuth angle and the radius in the yawed condition.The larger the yaw angle was,the larger the variation was.The pressure distribution in the spanwise sections was affected by both the angle of attack and the relative velocity.The angle of attack was more influential than the relative velocity.At the same yaw angle,when the angle of attack decreased,the c_(p)∼x/c curve shrunk inward and the lift force decreased.The larger the yaw angle was,the more obvious the shrink was.The effect of the yaw on the blade root region was higher than its effect on the blade tip region.
基金supported by the National Natural Science Foundation of China(No.11472157)
文摘Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.
基金Fund of Science and Technology on Underwater Information and Control Laboratory,Grant/Award Number:2021-JCJQ-LB-030-05。
文摘During the initial stage of vertical launch,a missile may exhibit an uncertain roll angle(φ)and a high angle of attack(α).This study focuses on examining the impact of roll angle variations on the flow field and the unsteady aerodynamics of a canard-configured missile atα=75°.Simulations were performed using the validated k-ωSST turbulence model.The analysis encompasses the temporal development of vortices,the oscillatory characteristics of the lateral force,and the fluctuation of kinetic energy distribution within the framework of proper orthogonal decomposition(POD).The results indicate that the flow field surrounding the canardconfigured missile is characterized by inconsistent shedding cycles of Kármán-like and canard-separated vortices.A distinct transition zone is identified between these vortices,where vortex tearing and reconnection phenomena occur.With increasing roll angles from 0°to 45°,there is an observed shift in the dominant frequency of the lateral force from the higher frequency associated with Kármán-like vortex shedding to the lower frequency of canard vortex shedding.The shedding frequency of Kármán-like vortices corresponds to the harmonics of the canard vortex shedding frequency,indicative of a higher-order harmonic resonance.The frequency of the lateral force is observed to decrease with an increase in roll angle,except in configurations lacking distinct canard-separated vortices,which are characterized by a“+”shape.The POD analysis reveals that the majority of the fluctuation energy is concentrated in the oscillations and shedding of the canard-separated vortices,leading to pressure fluctuations that are primarily observed on the canard and the downstream region of the canard.
文摘A numerical model has been developed for computing turbulent flow in plane-wall diffuser.The model solves the weakly compressible flow equations with the application of the Smagorinsky's subgrid-scale turbulence model and the boundary conditions of partial slip and no slip at the solid wall.Application examples include two-dimensional calculations of unstalled and stalled flows in diffusers of small diverging angle,as well as transitory stall flow in a symmetric diffuser of 16°total angle.For the unstalled and stalled flows,the calculated pressure recovery and velocity profile are compared with experimental data.For the transitory stall flow,the com- putational result shows the unsteady flow features including the vortex shedding and stall washout phenomena that have been experimentally observed.
文摘This paper presents the experimental investigations of high angle-of-attack flow con-trol on NACA0012 airfoil using vortex-generating devices in low speed wind tunnel. The vortex-generating devices used are (i) top-surface triangular wing type vortex-generators,(n) leading-edge vortex-generators, (iii) leading-edge slots. Experiment Renolds number range is 4.9×105 to 6.5×105, the angle-of-attack range is -10° to 20°. The comparisons of experimental results show that the vortex-generating devices can dramatically improve airfoil aerodynamic characteristics at normal stall angle-of-attack by increasing both the lift and the lift-to-drag ratio.
