查看更多>>摘要：Chatter in the machining system can result in a decrease in tool life,poor surface finish,conservative cutting parameters,etc.Despite many review papers promoting the understanding and research of this area,chatter suppression techniques are generally discussed within limited pages in the framework of comprehensive chatter-related problems.In recent years,the developments of smart materials,advanced sensing techniques,and more effective control strategies have led to some new progress in chatter suppression.Meanwhile,the widely used thin-walled parts present more and more severe machining challenges in their milling processes.Considering the above deficiencies,this paper summarizes the current state of the art in milling chatter suppression.New classifications of chatter suppression techniques are proposed according to the working principle and control target.Based on the new classified framework,the mechanism and comparisons of different chatter sup-pression strategies are reviewed.Besides,the current challenges and potential tendencies of milling chatter suppression techniques are highlighted.Intellectualization,integration,compactness,adapt-ability to workpiece geometry,and the collaboration of multiple control methods are predicted to be important trends in the future.
查看更多>>摘要：Multi-Source Information Fusion(MSIF),as a comprehensive interdisciplinary field based on modern information technology,has gained significant research value and extensive appli-cation prospects in various domains,attracting high attention and interest from scholars,engineer-ing experts,and practitioners worldwide.Despite achieving fruitful results in both theoretical and applied aspects over the past five decades,there remains a lack of comprehensive and systematic review articles that provide an overview of recent development in MSIF.In light of this,this paper aims to assist researchers and individuals interested in gaining a quick understanding of the relevant theoretical techniques and development trends in MSIF,which conducts a statistical analysis of academic reports and related application achievements in the field of MSIF over the past two dec-ades,and provides a brief overview of the relevant theories,methodologies,and application domains,as well as key issues and challenges currently faced.Finally,an analysis and outlook on the future development directions of MSIF are presented.
查看更多>>摘要：Micro-milling technology is widely applied in micro manufacturing,particularly for the fabrication of miniature and micro components.However,the chatters and machining dynamics related issues in micro-milling are often the main challenges restricting its machining quality and productivity.Many research works have rendered that the machining dynamics and chatters in micro-milling are more complex compared with the conventional macro-milling process,likely because of the size effect and rigidity of the micro-milling system including the tooling,workpiece,process variables,materials involved,and the high-speed milling machines,and further their collec-tive dynamic effects.Therefore,in this paper,the state of the art focusing on micro-milling chatters and dynamics related issues over the past years are comprehensively and critically reviewed to pro-vide some insights for potential researchers and practitioners.Firstly,typical applications and the problems caused by the machining dynamics and chatters in micro-milling have been put forward in this paper.Then,the research on the underlying micro-cutting mechanics and dynamics,stability analysis,chatters detection,and chatter suppression are summarized critically.Furthermore,the underlying scientific and technological challenges are discussed particularly against typical precision engineering applications.Finally,the possible future directions and trends in research and develop-ment of micro-milling have been discussed.
查看更多>>摘要：This paper focuses on the effect of the phase offset of Leading-Edge(LE)morphing on the aerodynamic characteristics of a pitching NACA0012 airfoil.Assuming an unstretched camber and using polynomial interpolation,an explicit expression for LE nonlinear morphing is proposed and implemented for the large pitching motion of the airfoil.Flow field results and aerodynamic forces are obtained by solving the unsteady Reynolds-averaged Navier-Stokes equations for both the airfoil's pitching motion and LE morphing.Furthermore,the index of instantaneous aerody-namic power is used to quantify the work done by the airflow in a dynamic process.According to the instantaneous aerodynamic power and energy map,which denotes the energy transfer between the airfoil's oscillation and flow field,the airfoil is subject to stall flutter.The results show that LE morphing with an optimal phase offset of 315° reduces the energy extraction from the flow field,suppressing the stall flutter instability.This optimal phase offset is effective at different pitch-ing axis positions of the airfoil.The results signify that LE morphing can suppress stall flutter by advancing the occurrence of the first LE vortex and increasing the nose-down moment during the upstroke period.
查看更多>>摘要：Deviation model is an important model for through-flow analysis in axial compressors.Theoretical analysis in classical deviation models is developed under the assumption of one-dimensional flow,which is controlled by the continuity equation.To consider three-dimensional characteristics in transonic flow,this study proposes an improved theoretical analysis method com-bining force analysis of the blade-to-blade flow with conventional analysis of the continuity equa-tion.Influences of shock structures on transverse force,streamwise velocity and streamline curvature in the blade-to-blade flow are analyzed,and support the analytical modelling of density flow ratio between inlet and outlet conditions.Thus,a novel deviation model for transonic stages in axial compressors is proposed in this paper.The empirical coefficients are corrected based on the experimental data of a linear cascade,and the prediction accuracy is validated with the experimental data of a three-stage transonic compressor.The novel model provides accurate predictions for meridional flow fields at the design point and performance curves at design speed,and shows obvi-ous improvements on classical models by Carter and Çetin.
查看更多>>摘要：Supersonic fuel film cooling is a promising way to simultaneously reduce the severe wall heat and friction load of the internal passage in a scramjet engine when operating at hypersonic con-ditions.Large eddy simulations were performed to investigate the cooling and wall friction charac-teristics of hydrogen and hydrocarbon films under inert and reactive circumstances.The results show that the essential difference of the turbulent state in the mixing layer contributes to the totally different behaviors of the cooling and wall friction reduction performances of the two fuel films.The turbulent transport processes between the hydrogen film and the mainstream are much weaker as compared to the case of hydrocarbon film,making inert hydrogen rather superior in cooling and friction reduction applications.Besides,the increase of wall temperature for hydrogen film under the inert case is mainly driven by the loss of hydrogen with high heat capacity instead of by direct heat addition.However,the film cooling performance severely deteriorates when the hydrogen film burns due to presence of severe heat release sources near the wall.On the other hand,combustion of hydrocarbon film in the boundary layer can remarkably improve its originally barely-satisfactory cooling and friction reduction performance to the level comparable to that of hydrogen film,due to the suppression of turbulent transport processes in the mixing layer and presence of heat absorp-tion sources near the wall.Overall,the hydrogen film is more advantageous in friction reduction,while the hydrocarbon film is more suitable for cooling.
查看更多>>摘要：Corner stall receives noticeable attention in the aeroengine field as an important phenomenon in highly-load compressors.Non-uniform leading-edge tubercles,as an effective method to delay stall,are introduced into the compressor.In this paper,the shape of leading-edge tubercles was controlled by a third-order Fourier function.To judge corner stall,a more precise stall indicator for compressor cascade with flow control methods was defined.Besides,the total kinetic energy of the secondary flow at large inci-dence was adopted as a parameter for stall evaluation to save computing resources.The results of multi-objective optimization reveal that the loss coefficient exhibited negligible variation at design incidence,while the total kinetic energy of secondary flow showed a significant reduction at large incidence,resulting in a substantial increase in stall incidence.In the optimal profiling cases,the stall incidence was delayed from 7.9° to 11.6°.The major purpose of the research is to provide proper design guidelines for non-uniform leading-edge tubercles and uncover the flow control mechanisms of leading-edge profiling.Hence,the geometric features that meet different optimization objectives were extracted through geometric anal-ysis near the Pareto Front and through Self-Organizing Map(SOM)data mining methods in the optimiza-tion database.Besides,flow field analysis reveals the flow control mechanism of leading-edge tubercles.The convex-concave-convex structure at the 0％-70％blade height region can form two branches of leading-edge vortex pairs that are opposite in the rotation direction to the passage vortex.The two branches of leading-edge vortex pairs mixed with the leading-edge separation vortex to form two stronger mixed vortices,which can effectively suppress the development of passage vortex and delay stall incidence.
查看更多>>摘要：The unpowered high-speed vehicle experiences a significant coupling between the disci-plines of aerodynamics and control due to its characteristics of high flight speed and extensive maneuverability within large airspace.The conventional aircraft conceptual design process follows a sequential design approach,and there is an artificial separation between the disciplines of aerody-namics and control,neglecting the coupling effects arising from their interaction.As a result,this design process often requires extensive iterations over long periods when applied to high-speed vehi-cles,and may not be able to effectively achieve the desired design objectives.To enhance the overall performance and design efficiency of high-speed vehicles,this study integrates the concept of Active Control Technology(ACT)from modern aircraft into the philosophy of aerodynamic/control inte-grated optimization.Two integrated optimization strategies,with differences in coupling granular-ity,have been developed.Subsequently,these strategies are put into action on a biconical vehicle that operates at Mach 5.The results reveal that the comprehensive performance of the synthesis optimal model derived from the aerodynamic/control integrated optimization strategy is improved by 31.76％and 28.29％respectively compared to the base model under high-speed conditions,demonstrating the feasibility and effectiveness of the method and optimization strategies employed.Moreover,in comparison to the single-stage strategy,the multi-stage strategy takes into deeper con-sideration the impact of control capacity.As a result,the control performance of the synthesis opti-mal model derived from the multi-stage strategy improves by 13.99％,whereas the single-stage strategy only achieves a 5.79％improvement.This method enables a fruitful interaction between aerodynamic configuration design and control system design,leading to enhanced overall perfor-mance and design efficiency.Furthermore,it improves the controllability of high-speed vehicles,mitigating the risk of mission failure resulting from an ineffective control system.
查看更多>>摘要：A new gas preparation system(GasPS-RCS)is proposed to solve two tasks:(A)to heat helium gas for tank pressurization;(B)to prepare gas for the Launch Vehicle(LV)Reactive Control System(RCS)at the LV orientation and stabilization sections of the LV on passive parts of the flight trajectory,to provide conditions for launching the Liquid Rocket Engine(LRE).The system includes a gas generator based on hydrogen peroxide,a separator for water separation,heat exchangers independent of the LRE,and gas-jet nozzles.The proposed new system allowed to reduce the length of pressurizing gas lines and reduce the increased helium gas consumption during the heat exchanger warm-up interval of the LRE during its launch.A special advantage of the pro-posed system is the possibility of ground testing of heat exchangers without an operating LRE.A mathematical model based on the first law of thermodynamics was used to perform a comparative analysis of GasPS-RCS with traditional pressurization and RCS systems.To validate the mathe-matical model,the experimental studies of helium pressurizing of a liquid nitrogen tank were con-ducted.The results show that the deviation of experimental and calculated values for pressure is 1.1％and for temperature up to 2％.According to the results of comparative analysis,the GasPS-RCS is 259 kg lighter for the first stage and 80 kg lighter for the second stage of the LV.
查看更多>>摘要：Plasma ignition technology has delivered good performance in the aerospace industry.In this study,a pre-combustion plasma jet igniter was designed,and its characteristics were examined from three aspects:the morphology,temperature,and discharge characteristics and process of igni-tion.Images of the OH distribution were obtained by using an OH Planar Laser-Induced Fluores-cence(OH-PLIF)experimental system.Results have shown that the proposed plasma jet had a higher OH concentration,longer length,and larger area than those of a traditional igniter.The sta-bility of discharge of the igniter was improved as the equivalence ratio φ was increased,and reduc-ing gas flow reduced the pulsation of the plasma jet.When the input current was increased from 15 A to 35 A,the highest average temperature increased from 5127 K to 7987 K.An increase in the equivalence ratio reduced the region of arc ionization,but expanded the regions of the core com-bustion reaction and the outer flame.Herein,this study has obtained a deep understanding of the jet and ignition law and developed a new idea for the application of plasma in the ignition field.A pre-combustion plasma jet igniter can significantly improve the efficiency of ignition and shorten the ignition process compared with a traditional igniter.
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