The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant importance for both academic field and engineering area.This paper attempts to provide an upda...The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant importance for both academic field and engineering area.This paper attempts to provide an update state of art to the investigations on the fields of forebody asymmetric vortices.This review emphasizes the correlation between micro-perturbation on the model nose and its response and evolution behaviors of the asymmetric vortices.The critical issues are discussed, which include the formation and evolution mechanism of asymmetric multi-vortices;main behaviors of asymmetric vortices flow including its deterministic feature and vortices flow structure;the evolution and development of asymmetric vortices under the perturbation on the model nose;forebody vortex active control especially discussed micro-perturbation active control concept and technique in more detail.However present understanding in this area is still very limited and this paper tries to identify the key unknown problems in the concluding remarks.展开更多
The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack...The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack. The bi-stable situation of the side forces is observed, which could be easily switched by a tiny disturbances either from coming flow or from artificial disturbances at nose tip （including manufacturing defect）. In turbulent flows the side forces switched randomly between positive and negative. There exists a hysteresis loop of side force with the rolling angle. A rod in front of the slender body is used to change the vortex pattern, which could be kept even the rod is moved out from the stream. A miniature strake attached to the nose tip of the model can be moved to different circumferential position. When the strake is stationary, the hysteresis loop disappears and the side force does not change with the turbulent fluctuation of coming flow. The results from dynamic measurements of section side force indicates that when the strake swung at lower frequency the side force can follow the cadence of the swinging strake. With increasing frequency, the magnitude of the side force decreases. At still high frequency, the side force diminishes to zero. If the strake is swinging, while the middle position can be changed to different circumferential angle Фs on either left or right side, the side forces can be changed proportionally with the angle Фs. On the basis of the experimental results, the mechanism of the asymmetry is discussed.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
针对现阶段软件定义网络(SDN)控制层流规则窜改攻击以及单点脆弱性问题,提出一种基于动态异构冗余的拟态安全控制器模型,通过分布式冗余架构以及一致性判决机制提高系统可靠性,利用调度机制实现系统动态性以及结合异构因素提高系统安全...针对现阶段软件定义网络(SDN)控制层流规则窜改攻击以及单点脆弱性问题,提出一种基于动态异构冗余的拟态安全控制器模型,通过分布式冗余架构以及一致性判决机制提高系统可靠性,利用调度机制实现系统动态性以及结合异构因素提高系统安全性,通过一致性容错算法(consistency and fault detection algorithm,CFDA)实现安全数据处理与错误检测,并提高控制器集群动态、可扩展性。仿真结果表明,对于控制器集群网络而言CFDA具有较低的通信复杂度,降低了节点冗余度要求;同时,冗余体的增加可以非线性降低系统被攻击成功概率,而适当的调度策略大大提高了系统安全率,因此拟态安全控制器机制能够有效提高攻击者攻击难度,增加系统安全可靠性。展开更多
由于工业控制系统(industrial control system,ICS)与物理环境紧密联系,其特有的序列攻击可通过将合法的操作注入到操作序列中的不合理位置上,迫使ICS进入异常状态,损毁设备,甚至破坏生态环境.目前,针对序列攻击检测的研究基本上是从信...由于工业控制系统(industrial control system,ICS)与物理环境紧密联系,其特有的序列攻击可通过将合法的操作注入到操作序列中的不合理位置上,迫使ICS进入异常状态,损毁设备,甚至破坏生态环境.目前,针对序列攻击检测的研究基本上是从信息流中提取操作序列进行检测,易受错误、虚假数据等情况的影响,导致检测精度受到限制.针对该问题,充分考虑ICS的操作与物理环境的相互依赖性,提出一种双流融合的工业控制异常检测机制,从物理环境中实时提取工业控制设备的状态信息组成设备状态流,并将其与信息流相融合,从操作次序和时序2个维度检测操作序列是否正常.同时利用设备状态流信息识别操作间隔中的工业控制设备的异常状态,提升异常检测范围和对操作时序异常的检测精度.实验结果表明:该方法能有效地识别序列攻击和部分工业控制设备的异常状态.展开更多
基金The project supported by the National Natural Science Foundation of China(10172017)Aeronautical Science Foundation of China(02A51048)Foundation of National Key Laboratory of Aerodynamic Design and Research(51462020504HK0101)
文摘The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant importance for both academic field and engineering area.This paper attempts to provide an update state of art to the investigations on the fields of forebody asymmetric vortices.This review emphasizes the correlation between micro-perturbation on the model nose and its response and evolution behaviors of the asymmetric vortices.The critical issues are discussed, which include the formation and evolution mechanism of asymmetric multi-vortices;main behaviors of asymmetric vortices flow including its deterministic feature and vortices flow structure;the evolution and development of asymmetric vortices under the perturbation on the model nose;forebody vortex active control especially discussed micro-perturbation active control concept and technique in more detail.However present understanding in this area is still very limited and this paper tries to identify the key unknown problems in the concluding remarks.
文摘The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack. The bi-stable situation of the side forces is observed, which could be easily switched by a tiny disturbances either from coming flow or from artificial disturbances at nose tip （including manufacturing defect）. In turbulent flows the side forces switched randomly between positive and negative. There exists a hysteresis loop of side force with the rolling angle. A rod in front of the slender body is used to change the vortex pattern, which could be kept even the rod is moved out from the stream. A miniature strake attached to the nose tip of the model can be moved to different circumferential position. When the strake is stationary, the hysteresis loop disappears and the side force does not change with the turbulent fluctuation of coming flow. The results from dynamic measurements of section side force indicates that when the strake swung at lower frequency the side force can follow the cadence of the swinging strake. With increasing frequency, the magnitude of the side force decreases. At still high frequency, the side force diminishes to zero. If the strake is swinging, while the middle position can be changed to different circumferential angle Фs on either left or right side, the side forces can be changed proportionally with the angle Фs. On the basis of the experimental results, the mechanism of the asymmetry is discussed.
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.
文摘针对现阶段软件定义网络(SDN)控制层流规则窜改攻击以及单点脆弱性问题,提出一种基于动态异构冗余的拟态安全控制器模型,通过分布式冗余架构以及一致性判决机制提高系统可靠性,利用调度机制实现系统动态性以及结合异构因素提高系统安全性,通过一致性容错算法(consistency and fault detection algorithm,CFDA)实现安全数据处理与错误检测,并提高控制器集群动态、可扩展性。仿真结果表明,对于控制器集群网络而言CFDA具有较低的通信复杂度,降低了节点冗余度要求;同时,冗余体的增加可以非线性降低系统被攻击成功概率,而适当的调度策略大大提高了系统安全率,因此拟态安全控制器机制能够有效提高攻击者攻击难度,增加系统安全可靠性。
文摘由于工业控制系统(industrial control system,ICS)与物理环境紧密联系,其特有的序列攻击可通过将合法的操作注入到操作序列中的不合理位置上,迫使ICS进入异常状态,损毁设备,甚至破坏生态环境.目前,针对序列攻击检测的研究基本上是从信息流中提取操作序列进行检测,易受错误、虚假数据等情况的影响,导致检测精度受到限制.针对该问题,充分考虑ICS的操作与物理环境的相互依赖性,提出一种双流融合的工业控制异常检测机制,从物理环境中实时提取工业控制设备的状态信息组成设备状态流,并将其与信息流相融合,从操作次序和时序2个维度检测操作序列是否正常.同时利用设备状态流信息识别操作间隔中的工业控制设备的异常状态,提升异常检测范围和对操作时序异常的检测精度.实验结果表明:该方法能有效地识别序列攻击和部分工业控制设备的异常状态.
