Research On Flow Mechanism And Intelligent Regulation Of A Novel Fluidic Thrust Vectoring Nozzle

Thrust vectoring technology,which can meet the performance requirements of future aircraft,such as unconventional mobility and agility,short-range/vertical takeoff and landing,supersonic cruise and high stealth,is one of the essential key technologies for future aircraft.Thrust vectoring nozzle is the core part of the thrust vectoring technology,and its performance determines the level of the engine technology.Fixed-geometry fluidic thrust vectoring nozzle has the advantages of simple structure,light weight,fast response,good invisibility,and high reliability.Especially,the dual throat nozzle developed on the basis of the throat shifting nozzle,which can not only achieve the best flow area control and thrust vectoring but also possess small loss and high thrust vectoring efficiency,is the first choice of thrust vectoring technology for future aircraft.In view of the urgent need of future aircraft for advanced thrust vectoring technology,especially high-performance fluidic thrust vectoring nozzle,this paper comprehensively utilizes the methods and means of theoretical analysis,numerical simulation and experimental research,and takes the novel bypass dual throat nozzle as the research object,combined with shape memory alloy and its actuator,develops the research on flow mechanism and intelligent regulation of the novel bypass dual throat nozzle.Firstly,an axisymmetric divergent bypass dual throat nozzle with fixed geometry is taken as the research object.By using the method of theoretical analysis and numerical simulation,the contents,which include the influences of the geometric parameters(cavity divergence angle,cavity convergence angle,cavity length,expansion ratio,rounding radii at the nozzle throat and cavity bottom,etc.)and aerodynamic parameters(mainly nozzle pressure ratio)on the starting characteristics of the nozzle,the method of solving the nozzle starting problem through a bypass and the influence of the bypass geometric parameters(bypass width,axial position of the bypass outlet and incident angle of the bypass,etc.)on the nozzle thrust performance,and the influences of three different computational domains(two-dimensional axisymmetric mesh,half of three-dimensional mesh,and full three-dimensional mesh)on the numerical simulation results,are studied.In addition,based on the results of numerical simulation,the starting characteristics of the nozzle are studied by using the existing exhaust system experimental platform of our research group.The results show that: the expansion ratio has the greatest influence on the starting characteristics of the nozzle,while the rounding radius at the cavity bottom is relatively small;the nozzle pressure ratio has a great influence on the starting characteristics of the nozzle,and before and after the critical nozzle pressure ratio of the nozzle thrust coefficient "sudden drop",the cavity presents the typical flow field structure in the started and unstarting states;by setting a bypass between the nozzle convergent section and the cavity divergent section,not only the starting problem of the nozzle can be solved,the thrust performance can be greatly improved,but also the fixed-geometry nozzle configuration can have certain capacity of flow regulation;the flow inside the cavity of the nozzle,especially in the separation zone,shows strong three-dimensional characteristics.Secondly,on the basis of the research results of nozzle starting characteristics,the influences of geometric parameters(expansion ratio,bypass width,rounding radii at the nozzle throat and cavity bottom,etc.)and aerodynamic parameters(nozzle pressure ratio and free flow Mach number)on the vector characteristics of the nozzle,as well as the flow adaptive capability of the nozzle are studied.In addition,based on the results of numerical simulation,the vector characteristics of the nozzle are studied by using the existing exhaust system experimental platform of our research group.The results show that: by appropriately arranging the bypass and properly controlling the bypass opening,the comprehensive performance under the non-vectored and vectored states are excellent,and the maximum pitch thrust-vector angle of the fixed-geometry axisymmetric divergent bypass dual throat nozzle with certain flow adaptive capability is 25.37°,the maximum thrust coefficient under the vectored state is 0.957,the maximum thrust coefficient under the non-vectored state is 0.921,and the discharge coefficient under the vectored state is the same as that under the non-vectored state,up to0.983.Thirdly,on the basis of the above research results,taking a variable axisymmetric divergent bypass dual throat nozzle as the research object,the motion design and structure design of the new variable axisymmetric divergent bypass dual throat nozzle throat and exit area intelligent regulation scheme based on shape memory alloy linear actuator are carried out.The results show that: the two nozzle intelligent regulation schemes,“slider-rocker mechanism & rotation” and “slider-rocker mechanism &slide”,can meet the design requirements of nozzle 50% throat area variations,and under the four states of non-afterburning non-vectored,non-afterburning vectored,afterburning non-vectored and afterburning vectored,by rotating the cavity convergent flap clockwise and anticlockwise around the slider,or sliding the cavity convergent flap upstream and downstream along the arc segment at the cavity bottom to control the nozzle exit area appropriately,the thrust coefficients under the non-afterburning non-vectored and afterburning non-vectored states can be greatly improved,and the nozzle can acquire certain flow adaptive capability during non-afterburning and afterburning;in the final nozzle intelligent regulation scheme,the sliders A and B are the active parts of slider-rocker mechanism which can change the nozzle throat area and slider like rocker mechanism which can change the nozzle exit area respectively,and the expansion ratio of the nozzle is always larger than 1during the movement of the sliders A and B.Finally,based on the motion design and structure design of the nozzle intelligent regulation scheme,the design of shape memory alloy linear actuator in the nozzle intelligent regulation scheme is carried out,and the corresponding validation experimental platform of the nozzle intelligent regulation scheme is built.Furthermore,under the cold laboratory environment,the driving performance of the shape memory alloy linear actuator in the nozzle intelligent regulation scheme is verified.The results show that: under the cold laboratory environment,for the shape memory alloy linear actuators of sliders A and B in the final nozzle intelligent regulation scheme,only two and one shape memory alloy wires are needed for these linear actuators to meet the reciprocating motion requirements for driving the sliders A and B;under the four states of non-afterburning non-vectored,non-afterburning vectored,afterburning non-vectored and afterburning vectored,the sliders A and B can move downstream from the initial position to the terminal position under the aerodynamic force of each nozzle flap,and stretch the shape memory alloy wires in the actuators to the specified strain.Meanwhile,for the sliders A and B,by electrically heating the shape memory alloy wires in the actuators,the actuators can also provide large recovery forces to ensure that the sliders A and B remain stable at the initial position of motion,or drive the sliders A and B to return to the initial position from the terminal position of motion.Through the above researches,the influences of geometric and aerodynamic parameters on the starting characteristics of the axisymmetric divergent bypass dual throat nozzle are obtained.The critical nozzle pressure ratio which can be used to judge whether the nozzle is “starting” is found,and in the wide nozzle pressure ratio working range,a fixed-geometry axisymmetric divergent bypass dual throat nozzle with certain flow adaptive capability and excellent comprehensive performance under the non-vectored and vectored states is obtained.In addition,a set of nozzle throat and exit area intelligent regulation scheme based on shape memory alloy linear actuator is also obtained.In a word,the overall scheme of nozzle intelligent regulation and control,which combines with the advantages of large flow regulation range mechanically and large thrust-vector angle,high thrust performance and fast dynamic response by fluidic methods,is “mechanical flow regulation & fluidic thrust vectoring”,which lays the foundation for the engineering application of the bypass dual throat nozzle.