查看更多>>摘要：Micro-vibration is an important factor affecting the imaging quality and pointing accu-racy of the in-orbit satellites.To address the problem of micro-vibration compensation,a general summary for modeling,analysis,suppression,and compensation approach should be outlined.In this review,micro-vibration characteristics and its impacts on the payloads are firstly analyzed.Afterwards,methods for micro-vibration measurement are provided.In detail,the principles and practical applications of these methods are introduced.Then,advanced technologies for micro-vibration suppression are summarized from micro-vibration source attenuation,transfer path opti-mization and sensitive load isolation.Two approaches have been found to be effective for micro-vibration compensation.The one is the Line-of-Sight(LOS)stabilization assisted with Inertial Ref-erence Unit(IRU).The other is using image restoration technology to remove the blur caused by platform jitter.The compensation technique and research status of the two techniques are reviewed.This work will provide researchers with technical guidelines for micro-vibration suppression.
查看更多>>摘要：Thermal Barrier Coatings(TBCs)technology is key to improving the service temperature and the productivity of aircraft engines.The performance and failure life of TBCs are strongly influ-enced by surface integrity and microstructure.Therefore,recognizing failure mechanisms and devel-oping effective surface treatment processes are crucial for further improving the reliability and durability of TBCs.This paper explains the primary reasons for TBC failure,emphasizing on how integrity of surface and interface influences interfacial oxidation,high-temperature erosion,and Calcium-Magnesium-Alumina-Silicate(CMAS)corrosion.Furthermore,this paper completely and rigorously evaluates the research status of TBCs surface treatment processes,including the characteristics and effects of various processes,and describes the requirements and goals of pre-treatment and post-treatment.In addition,a potential direction for the development and applica-tion of TBCs surface treatment is suggested.
查看更多>>摘要：In the context of increasing dimensionality of design variables and the complexity of con-straints,the efficacy of Surrogate-Based Optimization(SBO)is limited.The traditional linear and nonlinear dimensionality reduction algorithms are mainly to decompose the mathematical matrix composed of design variables or objective functions in various forms,the smoothness of the design space cannot be guaranteed in the process,and additional constraint functions need to be added in the optimization,which increases the calculation cost.This study presents a new parameterization method to improve both problems of SBO.The new parameterization is addressed by decoupling affine transformations(dilation,rotation,shearing,and translation)within the Grassmannian sub-manifold,which enables a separate representation of the physical information of the airfoil in a high-dimensional space.Building upon this,Principal Geodesic Analysis(PGA)is employed to achieve geometric control,compress the design space,reduce the number of design variables,reduce the dimensions of design variables and enhance predictive performance during the surrogate optimiza-tion process.For comparison,a dimensionality reduction space is defined using 95％of the energy,and RAE 2822 for transonic conditions are used as demonstrations.This method significantly enhances the optimization efficiency of the surrogate model while effectively enabling geometric con-straints.In three-dimensional problems,it enables simultaneous design of planar shapes for various components of the aircraft and high-order perturbation deformations.Optimization was applied to the ONERA M6 wing,achieving a lift-drag ratio of 18.09,representing a 27.25％improvement com-pared to the baseline configuration.In comparison to conventional surrogate model optimization methods,which only achieved a 17.97％improvement,this approach demonstrates its superiority.
查看更多>>摘要：Analysing the influence mechanism of the riblet protrusion height on turbulent drag components is more beneficial in organising the vortical structure over the riblet surface.Therefore,the Large Eddy Simulation(LES)is used to investigate the vortex structure over the rib-let surface with different protrusion heights.Then,the variations of Reynolds stress and viscous shear stress in a turbulent channel are analysed.As a result,the drag reduction rate increases from 3.4％when the riblets are completely submerged in the turbulent boundary layer to 7.9％when the protrusion height is 11.2.Further analysis shows that the protrusion height affects the streamwise vortices and the normal diffusivity of spanwise and normal vortices,thus driving the variation of Reynolds stress.Compared with the smooth surface,the vorticity strength and the number of streamwise vortices are weakened near the wall but increase in the logarithmic layer with increased protrusion height.Meanwhile,the normal diffusivity of spanwise vorticity decreases with the increase of protrusion height,and the normal diffusivity of normal vorticity is the smallest when the protrusion height is 11.2.Moreover,the protrusion height affects the velocity gradient of the riblet tip and riblet valley,thus driving the variation of viscous shear stress.With the increase of protrusion height,the velocity gradient of the riblet tip increases dramatically but decreases in the riblet valley.
查看更多>>摘要：Hollow cathode,with the highest plasma density,current density,and temperature,becomes one of the most important components in the electro-thruster system.As the electric-propulsion thruster performance is directly related to the ionization rate,reliability,and lifetime of the hollow cathode,this paper develops a global model to study the effects of discharge current,gas flow rate,and gas species on the discharge characteristics in the insert and orifice regions of the hollow cathode.The emitter wall temperatures of hollow cathodes predicted by the global model are compared with experimental results from NSTAR thruster neutralization cathodes,confirming the model's validity.The influence of hollow cathode emitter material and structure sizes on the plasma parameters in the internal regions was also evaluated.The simulation results show that there is an optimal matching relationship between the discharge current and gas flow rate to guarantee the maximum ionization rate.The optimal working region for the hollow cathode has been deter-mined under different energetic,regime and structural parameters.The global model established in this paper can quickly determine the key structure and operating parameters of hollow cathode at the design stage,and provide the theoretical basis for hollow cathode design and development.
查看更多>>摘要：Thrust vectoring technology plays an important role in improving the maneuverability of aircraft.In order to overcome the disadvantages of mechanical thrust vectoring nozzles,such as complications of structure and significant increases in weight and cost,fluidic thrust vectoring noz-zles are proposed.Dual Throat fluidic thrust vectoring Nozzle(DTN)has received wide attention due to its excellent thrust vectoring efficiency and minimal thrust loss.In this study,three-dimensional unsteady numerical simulations of a single axisymmetric DTN are conducted first to analyze its dynamic response.Then the pitch and yaw control characteristics of DTN equipped on a flying-wing aircraft are investigated.It is found that the dynamic response will experience three stages:rapid-deflecting stage,oscillating stage,and steady stage.A complete recirculation zone forms at the end of the rapid-deflecting stage,which pushes the primary flow to attach to the wall opposite the secondary injection.Meanwhile,the exhaust flow is deflected.In terms of DTN's appli-cation,the DTN equipped on the flying-wing aircraft is capable of providing effective pitch and yaw moments at all angles of attack and Mach numbers.In addition,continuous pitch and yaw moments can be obtained by adjusting the secondary mass flow ratios.The control moment is gen-erated due to the asymmetrical pressure distribution of nozzle surface,which is mainly contributed by the pressure decrease on the secondary injection surface.Moreover,the DTN equipped on the flying-wing aircraft has a relatively high thrust vectoring efficiency of around 5°/％and a thrust coefficient of around 0.95 when nozzle pressure ratio equals 4.These results provide an important theoretical basis for the practical application of DTN.
查看更多>>摘要：The spatiotemporal distribution characteristics of the regression rate are crucial aspects of the research on Hybrid Rocket Motor(HRM).This study presents a pioneering effort in achiev-ing a comprehensive numerical simulation of fluid dynamics and heat transfer in both the fluid and solid regions throughout the entire operation of an HRM.To accomplish this,a dynamic grid tech-nique that incorporates fluid-solid coupling is utilized.To validate the precision of the numerical simulations,a firing test is conducted,with embedded thermocouple probes being used to measure the inner temperature of the fuel grain.The temperature variations in the solid fuel obtained from both experiment and simulations show good agreement.The maximum combustion temperature and average thrust obtained from the simulations are found to deviate from the experimental results by only 3.3％and 2.4％,respectively.Thus,it can be demonstrated that transient numerical simu-lations accurately capture the fluid-solid coupling characteristics and transient regression rate.The dynamic simulation results of inner flow field and solid region throughout the entire working stage reveal that the presence of vortices enhances the blending of combustion gases and improves the regression rate at both the front and rear ends of the fuel grain.In addition,oscillations of the regression rate obtained in the simulation can also be well corresponded with the corrugated surface observed in the experiment.Furthermore,the zero-dimension regression rate formula and the for-mula describing the axial location dependence of the regression rate are fitted from the simulation results,with the corresponding coefficients of determination(R 2)of 0.9765 and 0.9298,respectively.This research serves as a reference for predicting the performance of HRM with gas oxygen and polyethylene,and presents a credible way for investigating the spatiotemporal distribution of the regression rate.
查看更多>>摘要：The problem of evaluating the sensitivity of non-trivial boundary conditions to the onset of azimuthal combustion instability is a longstanding challenge in the development process of mod-ern gas turbines.The difficulty lies in how to describe three-dimensional in-and outlet boundary conditions in an artificial computational domain.To date,the existing analytical models have still failed to quantitatively explain why the features of the azimuthal combustion instability of a com-bustor in laboratory environment are quite different from that in a real gas turbine,making the sta-bility control devices developed in laboratory generally lose the effectiveness in practical applications.To overcome this limitation,we provide a novel theoretical framework to directly include the effect of non-trivial boundary conditions on the azimuthal combustion instability.A key step is to take the non-trivial boundary conditions as equivalent distributed sources so as to uniformly describe the physical characteristics of the inner surface in an annular enclosure along with different in-and outlet configurations.Meanwhile,a dispersion relation equation is established by the application of three-dimensional Green's function approach and generalized impedance con-cept.Results show that the effects of the generalized modal reflection coefficients on azimuthal unstable modes are extremely prominent,and even prompt the transition from stable to unstable mode,thus reasonably explaining why the thermoacoustic instability phenomena in a real gas tur-bine are difficult to observe in an isolated combustion chamber.Overall,this work provides an effective tool for analysis of the azimuthal combustion instability including various complicated boundary conditions.
查看更多>>摘要：Uncertainties in the aerodynamic performance of compressors,introduced by manufac-turing variations,have received more and more attentions in recent years.The deviation model plays a crucial role in evaluating this uncertainty and facilitating robust design.However,current deviation models with a few variables cannot simultaneously achieve a precise geometric approxi-mation of deviation and provide an accurate assessment of performance uncertainty.This paper introduces a novel deviation modeling method named Nested Principal Component Analysis(NPCA)to break this tradeoff.In this method,both geometry-based and performance-based modes are utilized to describe manufacturing variations.By considering aerodynamic sensitivity,surface deformations that significantly impact aerodynamic performance can be extracted for deviation modeling.To demonstrate the superiority of this newly proposed method,ninety-eight newly man-ufactured compressor rotor blades were measured using a coordinate measurement machine,and both NPCA and Principal Component Analysis(PCA)were employed to model the real manufac-turing variations.The results indicate that,in comparison to the PCA method,the NPCA method achieves an equivalent level of accuracy in geometric reconstruction and evaluation of mean perfor-mance.Furthermore,the same level of accuracy can be obtained with eight NPCA modes and fifty PCA modes when assessing the scatter in aerodynamic performance.Finally,the working mecha-nism of the NPCA method for accurate uncertainty quantification was further investigated.
查看更多>>摘要：The Blended Blade and Endwall(BBEW)technique has proven to be effective in control-ling the intersection of boundary layer in corner region of the compressor endwall.In this study,the experiment and analysis of two different BBEW designs are emphasized.First,based on a linear cas-cade with 0.7 Mach number inflow,two different configurations,BBEW 1 and BBEW 2,are well conducted.Then,according to the experimental result,control effects of these two BBEW configu-rations are validated and compared subsequently under various working conditions.The results demonstrate a reduction in total pressure loss of 12.8％and 29％at the design point for BBEW 1 and BBEW 2,respectively.Consequently,the BBEW technique proves effective in suppressing the development of the boundary layer and preventing corner separation.Followed by detailed numerical analysis,improvements around the corner region,especially for the boundary layer,are extracted to show the mechanisms and distinctions between the two configurations.The results indicate that BBEW 1 significantly restrains the development of boundary layer before separation occurs,while BBEW 2 directly controls the strength and scale of the corner separation.
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