Study On Asymmetry Of Flow Around Slender Body Of Revolution At High Incidence And Asymmetry Control Using Minute Jets

By numerically simulating the flows around slender bodies of revolution at incidences, the interior laws of the flows are studied,and the influences of minute nose perturbation on the flows are also discussed.In addition,a new method to take active control on the flow asymmetry around slender bodies of revolution at high incidence is developed.Firstly,through analyzing the structures and the aerodynamic characteristics of the flows around slender bodies of revolution at different incidences to oncoming free stream,whose Mach number is alterable,several productions are achieved.(1)The axial evolution law on the structure and the aerodynamic characteristics of the asymmetric flows around slender bodies of revolution at incidences is summarized:whether the flow asymmetry is powerless or powerful,the flow always appears in the structure that lee-side vortices rise,and shed vortices form,and new lee-side vortices come into being alternately on opposite sides of a slender body of revolution axially from nose apex downstream to afterbody,and always induces the sectional side force of waving quasi-sinusoidally downstream axially.(2)Based on the idea of"vortex dividing and divided",a new forming mode of shed vortex and new lee-side vortex is advanced.It consists of two actual manners:Manner A-secondary vortex extrudes and divides the lee-side vortex on the same side;Manner B-remaining lee-side vortex extrudes and divides the rising leeside vortex on the opposite side.(3)The axial evolution laws on the forming manner of shed vortex and new lee-side vortex,which structure all different asymmetric vortical flows around slender bodies of revolution at incidences,are concluded.With the axial extent of the obvious symmetric vortex pattern near nose apex increasing,the axial evolution in turn appears in:(a) law x-forming manner transits from A to B step by step;(b)lawλ-forming manner transits from B to A at first,and then back to B step by step;(c) lawμ-all forming manners are B.Thereinto,the flows structured with law x are the most asymmetric,and the flows structured with lawλare less asymmetric,while the flows structured with lawμare the least asymmetric.(4)The correlations between the aerodynamic characteristics and the vortical structures of the flows around slender bodies of revolution at incidences are obtained.Downstream axially from nose apex to afterbody,a local sectional-side-force extremum always presents itself behind the forming of the corresponding shed vortex and new lee-side vortex.The magnitude of an extremum relies on both the forming manner of the corresponding shed vortex,new lee-side vortex and the intensity of the corresponding lee-side vortices.(5)The influences of incidence on the flows are also gained.With incidence increasing gradually in the range of asymmetric vortex pattern,the axial extent of the obvious symmetric vortex pattern near nose apex shortens by degrees and vanishes lastly,and the axial extent of the asymmetric vortex pattern shrinks towards the nose apex,and the axial evolution frequency of the asymmetric vortex pattern increases.In addition,the axial evolution of the forming manner of shed vortex and new lee-side vortex transits from law x to lawλ,and then to lawμstep by step,and the flow asymmetry boosts up by degrees.(6)The influences of Mach number of the oncoming free stream on the flows are reached,as well as.In the condition of subcritical Mach number(i.e.,when the flow is subsonic throughout the flow field),with Mach number increasing by degrees,the axial evolution of the forming manner of shed vortex and new lee-side vortex transits from lawμto lawλ,and then to law x step by step,and the flow asymmetry strengthens by degrees.While Mach number increasing unceasingly into supercritical range(i.e.,when supersonic flow begins to appear in the flow field),with Mach number increasing by degrees,the axial evolution of the forming manner of shed vortex and new lee-side vortex transits from law%to lawλ,and then to lawμstep by step,and the flow asymmetry weakens by degrees,instead. Secondly,the influences of nose-perturbation location on the flows around slender bodies of revolution at high incidence are investigated through analyzing the flows under different perturbation conditions.The results show that:(1)in allusion to the influences of perturbation axial location,there is one critical axial location of perturbation existing near nose apex;(2)in allusion to the influences of perturbation circumferential location,there are two critical circumferential locations existing for subsonic oncoming free streams and four for supersonic oncoming free streams.With perturbation shifting circumferentially step by step, the subsonic flows around slender bodies of revolution vary gradually in manner of single periodicity,while the supersonic flows vary gradually in manner of double periodicity.Thirdly,based on the point that the flow asymmetry originates from the aerodynamic instability existing in the original symmetric flow field,the forming process of the flow asymmetry is discussed respectively on the point of view of balance stability of nose vortices interacting and topological-structure stability of non-linear dynamic system.It indicates that two basics are necessary for the flows shifting from a symmetric one to an asymmetric one:(1) there are instable single-reattachment-point flow patterns existing in the symmetric flow field; (2)there are proper perturbations with sufficient energy existing in the symmetric flow field.Fourthly,the feasibility of employing minute jet vortex generator to control flow is verified by analyzing the action of inclined minute jets on flat-plate turbulent boundary layer. Minute jet vortex generator takes active control on the flow with the longitudinal vortices that originate from the interaction between inclined minute jets and boundary layer.Based on analyzing the influences of jet primary parameters on the control action,a new rule is disclosed:in order to carry out effective control on the flow with minute jet vortex generator, the longitudinal vortices originating from the interaction between inclined minute jets and boundary layer must be sufficient powerful and partially embedded in boundary layer when coming into being.Fifthly,via analyzing the action of minute jets symmetrically located near nose apex and upstream of the separation line on the flows around slender bodies of revolution at high incidence,the feasibility of employing minute jet vortex generator to control the flow asymmetry is confirmed.Minute jet vortex generator takes active control on the flow asymmetry with jet vortices that originate from the interaction between minute jets and the flow around slender bodies of revolution.Through the action of jet vortices on nose vortices, the asymmetry of nose vortices near nose apex weakens,and then the entire flow asymmetry around slender bodies of revolution weakens.By analyzing the influences of jet primary parameters on the control action,a rule is deduced:for taking effective control on the flow asymmetry,the jet vortices originating from the interaction between minute jets and the flow around slender bodies of revolution at incidences must be sufficient powerful,and close enough to nose vortices,and can take action on nose vortices in a sufficient long axial extent.