查看更多>>摘要：During the supersonic re-entry of multi-nozzle heavy rockets into the atmosphere,the basic flow state becomes increasingly complex due to the coupling effect between the retro-propulsion plumes and the freestream.A numerical method using the hybrid Reynolds-Averaged Navier-Stokes and Large Eddy Simulation(RES)method and discrete coordinate method is devel-oped to accurately estimate the thermal environment.In addition,finite rate chemical kinetics is used to calculate the afterburning reactions.The numerical results agree well with wind tunnel data,which confirms the validity and accuracy of the numerical method.Computations are conducted for the heavy carrier rocket re-entry from 53.1 km to 39.5 km altitude with 180° angle of attack by using three different Supersonic Retro-Propulsion(SRP)modes.The numerical results reveal that these three SRP flow fields are all Short Penetration Models(SPM).As the re-entry altitudes decrease,both the plume-plume interaction and the plume-freestream interaction become weaker.The highest temperatures in the plume shear layers of the three SRP modes increase by 8.36％,7.33％and 6.92％respectively after considering afterburning reactions,and all occur at a re-entry altitude of 39.5 km.As the rocket re-enters the atmosphere,the maximum heat flux on the rocket base plate of three SRP modes stabilizes at 290,170 and 200 kW/m2 respectively,but the maximum heat flux on the side wall increases significantly.When the altitude declines to 39.5 km,the extreme heat flux of the three modes increase by 84.16％,49.45％and 62.97％respec-tively compared to that at 53.1 km.
查看更多>>摘要：This paper presents an experimental and numerical study of the aerodynamics of a moderate-scale rotor hovering in the Extreme Ground Effect(EGE)where rotor height-off-ground is below half the rotor radius.The tip vortex field was visualized by using the PIV technique.The aerodynamic performance,tip vortex trajectory,wall jet characteristics,surface pressure and velocity fields were measured and analyzed.To explore more deeply the flow mechanisms of the extreme ground effect,Detached Eddy Simulation(DES)was conducted on completely structured meshes.The results showed significant deviations of the rotor performance in EGE from that in Regular Ground Effect(RGE)with the rotor heights of more than half the rotor radius.Moreover,the flow structures of the rotor in EGE are considerably complex,such as the wall jet and ground-wash flow separation.The rotor wake flow and tip vortices impact the ground more frequently,resulting in distinctive characteristics of the surface pressure and velocity fields in EGE.
查看更多>>摘要：To investigate the design strategy of highly loaded tandem cascades at both the midspan and endwall,the overall performance and flow mechanisms of four typical tandem cascades based on the optimization were analyzed from multiple perspectives numerically.The results show that the interference effects on the Front Blade(FB)and Rear Blade(RB)should not be overlooked dur-ing the design phase,and the design strategies at the midspan and endwall are completely different.At the midspan,the optimization aims to increase the interference effects and the strength of the gap jet while maintaining the same load on the FB and RB.However,the endwall optimal airfoil exhibits weakening interference effects,advancement of the gap jet location,and load transfer from the FB to RB.Through further analysis of flow characteristics,the midspan optimal airfoil is ben-eficial for inhibiting the low-energy fluid from interacting with the suction surface of RB under the design condition,but results in earlier occurrence of corner stall.The endwall optimal airfoil helps suppress the development of the secondary flow and delay the onset of corner stall.Furthermore,by combining the benefits of these two design approaches,additional forward sweep effects are achieved,further enhancing the performance of the tandem cascade.
查看更多>>摘要：Maneuvering flight substantially affects the dynamic behavior of rotors;particularly,such flight may cause rubbing between a rotor and stator,which is one of the most serious damages in aircraft engines.In this paper,a nonlinear dynamic model for describing the dynamic character-istics of a rub-impact rotor system during maneuvering flight is established based on the Lagrange equations.Subsequently,numerical simulations employing the Newmark method are performed,delving into the detailed discussion of the influence of parameters such as rotational speed and maneuvering flight on the transient and steady-state responses of the rotor system.The effect mech-anism of maneuver load and its coupling with rub impact is revealed.The results show that the impact response induced by maneuvering flight is more obvious in the subcritical state than in the supercritical state.The additional stiffness and damping are also induced;in particular,the additional damping has a coupling effect.Moreover,the rub impact imposes an additional con-straint on the rotor system,thereby weakening the influence of the maneuver load and becoming the major factor that determines the dynamic behavior of the rotor system at high speeds.
查看更多>>摘要：To address the challenges of high-dimensional constrained optimization problems with expensive simulation models,a Surrogate-Assisted Differential Evolution using Manifold Learning-based Sampling(SADE-MLS)is proposed.In SADE-MLS,differential evolution opera-tors are executed to generate numerous high-dimensional candidate points.To alleviate the curse of dimensionality,a Manifold Learning-based Sampling(MLS)mechanism is developed to explore the high-dimensional design space effectively.In MLS,the intrinsic dimensionality of the candidate points is determined by a maximum likelihood estimator.Then,the candidate points are mapped into a low-dimensional space using the dimensionality reduction technique,which can avoid signif-icant information loss during dimensionality reduction.Thus,Kriging surrogates are constructed in the low-dimensional space to predict the responses of the mapped candidate points.The candidate points with high constrained expected improvement values are selected for global exploration.Moreover,the local search process assisted by radial basis function and differential evolution is per-formed to exploit the design space efficiently.Several numerical benchmarks are tested to compare SADE-MLS with other algorithms.Finally,SADE-MLS is successfully applied to a solid rocket motor multidisciplinary optimization problem and a re-entry vehicle aerodynamic optimization problem,with the total impulse and lift to drag ratio being increased by 32.7％and 35.5％,respec-tively.The optimization results demonstrate the practicality and effectiveness of the proposed method in real engineering practices.
查看更多>>摘要：Noise reduction program design is an effective approach that relies on efficient noise pre-diction for reducing ground noise during flight.The existing noise prediction methods have the lim-itations of being computationally expensive or only applicable to far-fields.In this paper,a High-Efficiency Prediction Method(HEPM)for helicopter global/ground noise based on near-field acoustic holography is proposed.The HEPM can predict the global noise based on acoustic modal analysis and has the advantages of high prediction accuracy and low time cost.The process is given as follows:firstly,the rotor noise on the holographic surface in the specified flight is obtained by simulations or experiments.Secondly,the global noise model,which maps time-domain noise to acoustic modes,is established based on near-field acoustic holography and Fourier acoustic analysis methods.Finally,combined with acoustic modal amplitude,the model established enables effi-ciently predicting the global/ground noise in the corresponding flight state.To verify the accuracy of the prediction method,a simulation study is conducted in hovering and forward flight states using a model helicopter with a 2-meter rotor and Rotor Body Interaction(ROBIN)fuselage.The comparison of HEPM with numerical results shows that the average prediction errors of the global and ground noise are less than 0.3 dB and 0.2 dB,respectively.For a region containing 100000 observers,the computation time of the HEPM is only one-fifth of that of the acoustic hemi-sphere method,demonstrating the rapidity of the proposed method.
查看更多>>摘要：Climate warming and the increased demand in air travels motivate the aviation industry to urgently produce technological innovations.One of the most promising innovations is based on the smoothly continuous morphing leading-edge concept.This study proposes a two-step process for the design of a morphing leading-edge,including the optimization of the outer variable-thickness composite compliant skin and the optimization of the inner kinematic mechanism.For the compliant skin design,an optimization of the variable thickness composite skin is proposed based on a laminate continuity model,with laminate continuity constraint and other manufacturing constraints.The laminate continuity model utilizes a guiding sequence and a ply-drop sequence to describe the overall stacking sequence of plies in different thickness regions of the complaint skin.For the inner kinematic mechanism design,a coupled four-bar linkage system is proposed and optimized to produce specific trajectories at the actuation points on the stringer hats of the compliant skin,which ensures that the compliant skin can be deflected into the aerodynamically optimal profile.Finally,a morphing leading-edge is manufactured and tested.Experi-mental results are compared with numerical predictions,confirming the feasibility of the morphing leading-edge concept and the overall proposed design approach.
查看更多>>摘要：As one of the core modules for air traffic flow management,Air Traffic Flow Prediction(ATFP)in the Multi-Airport System(MAS)is a prerequisite for demand and capacity balance in the complex meteorological environment.Due to the challenge of implicit interaction mechanism among traffic flow,airspace capacity and weather impact,the Weather-aware ATFP(Wa-ATFP)is still a nontrivial issue.In this paper,a novel Multi-faceted Spatio-Temporal Graph Convolutional Network(MSTGCN)is proposed to address the Wa-ATFP within the complex operations of MAS.Firstly,a spatio-temporal graph is constructed with three different nodes,including airport,route,and fix to describe the topology structure of MAS.Secondly,a weather-aware multi-faceted fusion module is proposed to integrate the feature of air traffic flow and the auxiliary features of capacity and weather,which can effectively address the complex impact of severe weather,e.g.,thunder-storms.Thirdly,to capture the latent connections of nodes,an adaptive graph connection construc-tor is designed.The experimental results with the real-world operational dataset in Guangdong-Hong Kong-Macao Greater Bay Area,China,validate that the proposed approach outperforms the state-of-the-art machine-learning and deep-learning based baseline approaches in performance.The case study of convective weather scenarios further proves the adaptability of the proposed approach.
查看更多>>摘要：To address the problem that model uncertainty and unknown time-varying system noise hinder the filtering accuracy of the autonomous navigation system of satellite constellation,an autonomous navigation method of satellite constellation based on the Unscented Kalman Filter with Adaptive Forgetting Factors(UKF-AFF)is proposed.The process noise covariance matrix is estimated online with the strategy that combines covariance matching and adaptive adjustment of forgetting factors.The adaptive adjustment coefficient based on squared Mahalanobis distance of state residual is employed to achieve online regulation of forgetting factors,equipping this method with more adaptability.The intersatellite direction vector obtained from photographic observations is introduced to determine the constellation satellite orbit together with the distance measurement to avoid rank deficiency issues.Considering that the number of available measure-ments varies online with intersatellite visibility in practical applications such as time-varying con-stellation configurations,the smooth covariance matrix of state correction determined by innovation and gain is adopted and constructed recursively.Stability analysis of the proposed method is also conducted.The effectiveness of the proposed method is verified by the Monte Carlo simulation and comparison experiments.The estimation accuracy of constellation position and velocity of UKF-AFF is improved by 30％and 44％respectively compared to those of the extended Kalman filter,and the method proposed is also better than other several adaptive filtering methods in the presence of significant model uncertainty.
查看更多>>摘要：A space-based bistatic radar system composed of two space-based radars as the transmit-ter and the receiver respectively has a wider surveillance region and a better early warning capability for high-speed targets,and it can detect focused space targets more flexibly than the monostatic radar system or the ground-based radar system.However,the target echo signal is more difficult to process due to the high-speed motion of both space-based radars and space targets.To be speci-fic,it will encounter the problems of Range Cell Migration(RCM)and Doppler Frequency Migra-tion(DFM),which degrade the long-time coherent integration performance for target detection and localization inevitably.To solve this problem,a novel target detection method based on an improved Gram Schmidt(GS)-orthogonalization Orthogonal Matching Pursuit(OMP)algorithm is proposed in this paper.First,the echo model for bistatic space-based radar is constructed and the conditions for RCM and DFM are analyzed.Then,the proposed GS-orthogonalization OMP method is applied to estimate the equivalent motion parameters of space targets.Thereafter,the RCM and DFM are corrected by the compensation function correlated with the estimated motion parameters.Finally,coherent integration can be achieved by performing the Fast Fourier Transform(FFT)operation along the slow time direction on compensated echo signal.Numerical simulations and real raw data results validate that the proposed GS-orthogonalization OMP algo-rithm achieves better motion parameter estimation performance and higher detection probability for space targets detection.
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