Milling surface roughness for 7050 aluminum alloy cavity influenced by nozzle position of nanofluid minimum quantity lubrication

In nanofluid minimum quantity lubrication (NMQL) milling of aviation aluminum alloy, it is the bottleneck problem to adjust the position parameters (target distance, incidence angle, and elevation angle) of the nozzle to improve the surface roughness of milling, which has large and uncontrollable errors. In this paper, the influence law of milling cutter speed, helical angle, and cavity shape on the flow field around the milling cutter was studied, and the optimal nozzle profile parameters were obtained. Using 7050 aluminum alloy as the workpiece material, the milling experiment of the NMQL cavity was conducted by utilizing cottonseed oil-based Al₂O₃ nanofluid. Results show that the high velocity of the surrounding air flow field and the strong gas barrier could be attributed to high rotating velocities of the milling cutter. The incidence angle of the nozzle was consistent with the helical angle of the milling cutter, the target distance was appropriate at 25–30 mm, and the elevation angle was suitable at 60°–65°. The range and variance analyses of the signal-to-noise ratio of milling force and roughness were performed, and the chip morphology was observed and analyzed. The results show that the optimal combination of nozzle position parameters was the target distance of 30 mm, the incidence angle of 35°, and the elevation angle of 60°. Among these parameters, target distance had the largest impact on cutting performance with a contribution rate of more than 55%, followed by incidence angle and elevation contribution rate. Analysis by orthogonal experiment revealed that the nozzle position parameters were appropriate, and R_a (0.087 μm) was reduced by 30.4% from the maximum value (0.125 μm). Moreover, R_sm (0.05 mm) was minimum, which was 36% lower than that of the seventh group (R_sm = 0.078 mm).     

叶片型面精密振动电解加工工艺研究

采用电解加工工艺对叶片型面进行加工,可以有效提高发动机叶片加工效率,降低生产成本。针对GH4169G合金叶片型面,开展了精密振动电解加工试验研究。结果表明:高频脉冲电流和阴极机械振动具有改善极间流场特性、降低阳极钝化和阴极的产物吸附的作用,可以大幅改善加工效果;采用参数组加工电压15V、阴极振动频率25Hz、开通角度Ra 150°~195°、脉冲频率3000Hz时,获得最优的型面加工质量,型面轮廓度为-0.012~+0.013mm,表面粗糙度值为0.51μm,证明精密振动电解加工工艺满足叶片型面的加工要求。     

Effects of surface roughness on the aerodynamic performance of a high subsonic compressor airfoil at low Reynolds number

The aerodynamic performance of compressor airfoil is significantly affected by the surface roughness at low Reynolds number (Re). In the present study, numerical simulations have been conducted to investigate the impact of surface roughness on the profile loss of a high subsonic compressor airfoil at Re = 1.5 × 10⁵. Four roughness locations, covering 10%, 30%, 50% and 100% of the suction surface from the leading edge and seven roughness magnitudes (R_a) ranging from 52 to 525 μm were selected. Results showed that the surface roughness mainly determined the loss generation process by influencing the structure of the Laminar Separation Bubble (LSB) and the turbulence level near the wall. For all the roughness locations, the variation trend for the profile loss with the roughness magnitude was similar. In the transitionally rough region, the negative displacement effect of the LSB was suppressed with the increase of roughness magnitude, leading to a maximum decrease of 14.6%, 16.04%, 16.45% and 10.20% in the profile loss at R_a = 157 μm for the four roughness locations, respectively. However, with a further increase of the roughness magnitude in the fully rough region, the stronger turbulent dissipation enhanced the growth rate of the turbulent boundary layer and increased the profile loss instead. By comparison, the leading edge roughness played a dominant role in the boundary layer development and performance variation. To take fully advantage of the surface roughness reducing profile loss at low Re, the effects of roughness on suppressing LSB and inducing strong turbulent dissipation should be balanced effectively.     

适应较大叶型弯角范围的轴流压气机落后角模型

通过对多种落后角模型进行研究对比,选出其中一组,并对设计状态落后角模型重新修正,在此基础上结合S1流场计算发展了一种适用于轴流压气机落后角预测的模型.另对非设计状态落后角计算采用了修正模型.结果表明:建立的计算程序在一定的攻角范围内,对S1流场的预测结果是比较准确的,通过多组平面叶栅验证,在叶型弯角较大或者较小时,设计状态落后角模型预测精度均提高,误差范围控制在1°以内;建立的轴流压气机落后角预测模型,对多组轴流压气机设计状态落后角预测,误差都不超过2°,初步验证了模型的有效性.     

Optimization of flow field in electrochemical trepanning of integral cascades (Ti6Al4V)

Ti6Al4V is widely applied in the integral cascades of aero engines. As an effective machining method, electrochemical trepanning (ECTr) has unique advantages in processing surface parts made of hard-to-cut materials. In ECTr, the state of the flow field has a significant effect on processing stability and machining quality. To improve the uniformity of the flow field when ECTr is applied to Ti6Al4V, two different flow modes are designed, namely full-profile electrolyte supply (FPES) and edges electrolyte supply (EES). Different from the traditional forward flow mode, the flow directions of the electrolyte in the proposed modes are controlled by inlet channels. Simulations show that the flow field under EES is more uniform than that under FPES. To further enhance the uniformity of the flow field, the structure of EES is optimized by modifying the insulating sleeve. In the optimized configuration, the longitudinal distance between the center of the inlet hole and the center of the blade is 6.0 mm, the lateral distance between the centers of the inlet holes on both sides is 16.5 mm, the length to which the electrolyte enters the machining area is 1.5 mm, and the height of the insulating sleeve is 13.5 mm. A series of ECTr experiments are performed under the two flow modes. Compared with EES, the blade machined by FPES is less accurate and has poorer surface quality, with a surface roughness (R_a) of 3.346 μm. Under the optimized EES, the machining quality is effectively enhanced, with the surface quality improved from R_a = 2.621 μm to R_a = 1.815 μm, thus confirming the efficacy of the proposed methods.     

High-energy gamma-astronomy with large underground detectors

Large underground (underwater) detectors (such as ‘Baikal’ and DUMAND) are discussed for their possible use as gamma-ray telescopes. The signal is caused by high-energy muons (E _μ ? 30–100 TeV) produced by the primary gamma-radiation in the Earth's atmosphere. The production of gamma-rays in the source through the reaction p + p → π ⁰ + X is calculated for a low density target of arbitrary thickness taking the electromagnetic cascade into account. The muon production by gamma-rays in the Earth's atmosphere is calculated using three processes: (i) photoproduction of π- and K-mesons followed by decay to muons, (ii) the direct production of μ⁺ μ^?-pairs: γ + Z → Z + μ ⁺ + μ^?, and (iii) photoproduction of charmed particles. It is shown that for thin sources with a flat spectrum (integral exponent γ = 1.1) a large (S = 0.1 km²) underground detector can detect both neutrinos and gamma-quanta generated by the source. Finally we compare the performances of underground detectors with S = 0.1 km² for the search of gamma sources at E = 100 TeV with those of the previously proposed 1 km² EAS array.     

多级考虑冷气掺混流片变厚度的S_1流面研究

为减少气冷涡轮气动设计难度,提出一套基于多级气冷涡轮考虑冷气掺混及随流道翘曲、变厚度的S1流面计算思路,编制了带冷气的翘曲S1流面薄片计算的参数化方法程序及网格自动生成程序,改良了传统平面薄片,对比分析了改良后平面薄片、翘曲S1流面薄片以及三维计算间差异,对某高压涡轮进行了翘曲S1流面薄片气动优化.结果显示:与三维计算对比,改良后平面薄片最大流量差距为22.68%,翘曲S1流面薄片为3.58%,一维数据上翘曲S1流面薄片更逼近三维计算;型面压力分布及马赫数云图分布上翘曲面S1流面薄片较改良后平面薄片更贴近三维计算;采用翘曲S1流面薄片进行优化后,效率较原始方案提升0.41%,流量较原始方案仅增加0.21%.     

横向气流中液体圆柱射流的破碎特性和表面波现象

采用高速摄像仪对横向气流场中的圆形液体射流的圆柱破碎过程(低Weber数)进行了实验研究.实验采用直射式喷嘴,喷孔直径为0.3mm和0.5mm,喷嘴长径比均为40.实验工质采用水.Weber数为1.7~7,液/气动量通量比为3.4~83.实验观察了表面波现象及射流破碎形成的液滴的尺寸及其速度.观测发现,表面波波长随着气流Weber数的对数的增加而线性减小.破碎后形成的液滴直径 d_p/d₀与Weber数的对数成正比.液滴的初始x方向速度与y方向速度大小与液滴直径无关.在实验范围内,液滴y方向速度均不随Weber数和液/气动量通量比的变化,约为初始射流速度的0.94倍;而液滴x方向速度约为0.085倍的气流速度.对表面波和破碎后形成的液滴尺寸及速度的研究有助于构建更精确的初始雾化模型.      

Optimization of GTE blade milling parameters on NC machines

In this paper, the procedure of optimizing the milling conditions of GTE blade duct surfaces on NC machines with the use of minimal labor intensity criterion is presented. Depending on a degree of the blade surface curvature and assuming that the feed to the tooth S _z is constant, the control of the minute feed rate S _min is executed.     

多电极偶接对金属大气腐蚀影响的试验与仿真

搭建薄液膜厚度测量与控制装置,采用微距参比电极后置法组建三电极体系,测量了厚度为100 μm的3.5wt% NaCl液膜下2A12铝合金、TC18钛合金和30CrMnSiNi2A高强钢的极化曲线和耦合体系的电偶电流;建立了基于薄壳电流分布的Comsol腐蚀仿真模型,得到了100 μm液膜下电极电位分布和电流密度分布图,通过对电极表面进行局部电流面积分计算得到了其电偶电流,对不同电极进行了面积的参数化扫描,讨论分析了不同面积比对于电偶电流的影响。结果表明：利用仿真模型得到的电偶电流值与试验值吻合较好,在2A12/30CrMnSiNi2A/TC18多电极体系中2A12充当阳极,TC18/30CrMnSiNi2A充当阴极,且阴阳极极性不随面积比的变化而发生转变,电偶电流主要集中在30CrMnSiNi2A与2A12之间,电偶电流与TC18面积呈线性关系,其对数与2A12和30CrMnSiNi2A面积的对数之间呈线性关系。利用建立的仿真模型对模拟搭接件大气腐蚀进行了仿真研究,仿真发现垫圈、2A12与30CrMnSiNi2A偶接接缝处及2A12与TC18偶接铆钉处电流密度分布更为集中,易发生腐蚀,与暴晒试验结果相符,说明该仿真模型对于多电极偶接的腐蚀分布具有很好的预测作用。     

Dimension Accuracy and Surface Integrity of Creep Feed Ground Titanium Alloy with Monolayer Brazed CBN Shaped Wheels

Titanium alloy tenon is creep feed ground with monolayer brazed cubic boron nitride (CBN) shaped wheels. The dimension accuracy of the tenon is assessed and the results indicate that it completely meets the requirement of blade tenon of aero-engine. Residual stresses, surface roughness, microstructure and microhardness are measured on ground surfaces of the specimen, which are all compared with that ground with vitrified CBN wheels. Under all the circumstances, compressive residual stress is obtained and the depth of the machining affected zone is found to be less than 40 μm. No phase transformation is observed at depths of up to 100 μm below the surface, though plastic deformation is visible in the process of grain refinement. The residual stress and microhardness of specimens ground with brazed CBN wheels are observed to be lower than those ground with vitrified ones. The arithmetic mean roughness (R_a) values obtained are all below 0.8 μm.     

A plastic strain energy method exploration between machined surface integrity evolution and torsion fatigue behaviour of low alloy steel

To explore the evolution mechanism of multistage machining processes and torsional fatigue behaviour based on strain energy for the first time and provide process optimization of axis parts of low alloy steel for service performance, four multistage machining processes were applied to the 45Cr Ni Mo VA steel, including the Rough Turning process(RT), RT+ the Finish Turning process(FRT), FRT+ the Grinding process(GFRT) and RT+ the Finish Turning process on dry cutting condition(FRT0). The result s...     

Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets

The spins of ten stellar black holes have been measured using the continuum-fitting method. These black holes are located in two distinct classes of X-ray binary systems, one that is persistently X-ray bright and another that is transient. Both the persistent and transient black holes remain for long periods in a state where their spectra are dominated by a thermal accretion disk component. The spin of a black hole of known mass and distance can be measured by fitting this thermal continuum spectrum to the thin-disk model of Novikov and Thorne; the key fit parameter is the radius of the inner edge of the black hole’s accretion disk. Strong observational and theoretical evidence links the inner-disk radius to the radius of the innermost stable circular orbit, which is trivially related to the dimensionless spin parameter a _? of the black hole (|a _?|<1). The ten spins that have so far been measured by this continuum-fitting method range widely from a _?≈0 to a _?>0.95. The robustness of the method is demonstrated by the dozens or hundreds of independent and consistent measurements of spin that have been obtained for several black holes, and through careful consideration of many sources of systematic error. Among the results discussed is a dichotomy between the transient and persistent black holes; the latter have higher spins and larger masses. Also discussed is recently discovered evidence in the transient sources for a correlation between the power of ballistic jets and black hole spin.     

Quantification of parametric uncertainty in γ-Reθ model for typical flat plate and airfoil transitional flows

Owing to the lack of physical knowledge of boundary layer transition, the γ-Re_θ transition model introduces closure parameters, which increase the uncertainty of transition prediction. The objective of this work is to quantify the uncertainties of closure parameters in the quantities of interests and identify the key parameters. The six closure parameters in the uncertainty intervals are used as input variables, and the uncertainties of the output results are propagated by a stochastic expansion based on the point-collocation nonintrusive polynomial chaos method. The relative contribution of each parameter to uncertainty is evaluated by the Sobol index. The computational cases include natural and bypass transitional flows on zero-pressure-gradient flat plates, and subsonic and transonic flows around airfoils. For most cases, c_e2, c_a2, and c_a1 dominate the uncertainty, and the influence of σ_θt is also significant when the history effects of flow are evident. The contribution of parameters in airfoils is more complex than that in flat plates. The transonic airfoil case shows that flow separation dramatically changes the distribution of Sobol indices, which poses a challenge to the accurate prediction of transition. Generally, c_e2 and c_a2 are the key parameters of the γ-Re_θ model.     

Corrosion Inhibition of SiC_p/5A06 Aluminum Metal Matrix Composite by Cerium Conversion Treatment

This article studies the effects of the CeCl₃ concentrations in conversion solutions with and without addition of NaCl, pH-values of conversion solution, drying temperature, time and temperature of immersion on the Ce-conversion coatings for corrosion protection of the SiC_p/5A06 Al-MMC and 5A06 Al-alloy in the 3.5% NaCl aqueous solution at room temperature. Potentiodynamic polarization tests reveal that the Ce-conversion treatment could markedly improve the pitting corrosion resistance of the composite and the matrix alloy in chloride containing environment. The best corrosion resistance effects are obtained for the samples treatment in 1‰ CeCl₃·7H₂O/ 3.5% NaCl solution at 45 °C for 60 min, followed by drying at 100 °C for 30 min. Examinations by means of scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) indicate that this behavior is due to the precipitation of Ce-oxides/hydroxides on the cathodic intermetallics and the Al-oxide film on the rest of the metal matrix.     

Stress corrosion behavior of 2195-T8 Al-Li alloy with an artificial pit exposed to a 30vol% HNO3 solution

This paper experimentally studied the stress corrosion behavior of 2195-T8 Al-Li alloys with prefabricated pits in 30vol% HNO₃. The microstructure was observed and determined by the scanning electron microscopy and the transmission electron microscopy. The typical corrosion features, i.e., regular or irregular corrosion pits and sub/intergranular corrosion, were investigated, and the role of stress were analyzed. The statistical results of the number and area of corrosion pits in various sizes were studied using an improved image processing method. Experimental results demonstrate that stress affects the intergranular corrosion or sub-intergranular corrosion of the alloy most, and promotes them to evolve into cracks under stress corrosion. Stress also plays a role in accelerating corrosion severity of certain corrosion feature. The number of corrosion pits with an area of 0–50 μm² can be seen as an index to reflect the degree of corrosion. Besides, a corrosion phenomenon, i.e., the pit bottom in the site with the maximum stress locally suffering from no severe corrosion, was observed and discussed.     

RANS simulations on combustion and emission characteristics of a premixed NH3/H2 swirling flame with reduced chemical kinetic model

Ammonia (NH₃) is considered as a potential alternative carbon free fuel to reduce greenhouse gas emission to meet the increasingly stringent emission requirements. Co-burning NH₃ and H₂ is an effective way to overcome ammonia’s relative low burning velocity. In this work, 3D Reynolds Averaged Navier-Stokes (RANS) numerical simulations are conducted on a premixed NH₃/H₂ swirling flame with reduced chemical kinetic mechanism. The effects of (A) overall equivalence ratio Φ and (B) hydrogen blended molar fraction X_H2 on combustion and emission characteristics are examined. The present results show that when 100%NH₃-0%H₂-air are burnt, the NO emission and unburned NH₃ of at the swirling combustor outlet has the opposite varying trends. With the increase of Φ, NO emission is found to be decreased, while the unburnt ammonia emission is increased. NH₂ → HNO, NH → HNO and HNO → NO sub-paths are found to play a critical role in NO formation. Normalized reaction rate of all these three sub-paths is shown to be decreased with increased Φ. Hydrogen addition is shown to significantly increase the laminar burning velocity of the mixed fuel. However, adding H₂ does not affect the critical equivalence ratio corresponding to the maximum burning velocity. The emission trend of NO and unburnt NH₃ with increased Φ is unchanged by blending H₂. NO emission with increased X_H2 is increased slightly less at a larger Φ than that at a smaller Φ. In addition, reaction rates of NH₂ → HNO and HNO → NO sub-paths are decreased with increased X_H2, when Φ is larger. Under all tested cases, blending H₂ with NH₃ reduces the unburned NH₃ emission, especially for rich combustion conditions. In summary, the present work provides research finding on supporting applying ammonia with hydrogen blended in low-emission gas turbine engines.     

Effect of ultrasonic vibration on finished quality in ultrasonic vibration assisted micromilling of Inconel718

Inconel718 was machined with the traditional micromilling (TMM) and ultrasonic vibration assisted micromilling (UVAMM) with the different technology parameters, whose surface quality and burrs formation were studied. The results show that TMM often forms pits, bumps and gullies in the size effect range. UVAMM effectively improves the surface quality compared with TMM. The surface defects are significantly reduced with the increase of feed per tooth (ƒ_z). When ƒ_z exceeds 4 μm, the effect of ultrasonic vibration on the surface quality is no longer obvious. The minimum burr size on the down milling side and the up milling side are 50.23 μm and 36.57 μm, respectively. The feasibility of vibration cutting in improving surface quality and suppressing burr size was verified. UVAMM effectively suppresses the formation of built-up edge, which can significantly improve the micromilling process. The cutting force is obtained through simulation and experiment. They are agreement in the change trend. The finite element simulation can be used to predict the cutting force. Compared with TMM, feeding force (F_x), radial force (F_y) and axial force (F_z) of UVAMM decrease by 7.6%, 11.5% and 1.3%, respectively.     

Ages and Geologic Histories of Martian Meteorites

We review the radiometric ages of the 16 currently known Martian meteorites, classified as 11 shergottites (8 basaltic and 3 lherzolitic), 3 nakhlites (clinopyroxenites), Chassigny (a dunite), and the orthopyroxenite ALH84001. The basaltic shergottites represent surface lava flows, the others magmas that solidified at depth. Shock effects correlate with these compositional types, and, in each case, they can be attributed to a single shock event, most likely the meteorite's ejection from Mars. Peak pressures in the range 15 – 45 GPa appear to be a "launch window": shergottites experienced ～30 – 45 GPa, nakhlites ～20 ± 5 GPa, Chassigny ～35 GPa, and ALH84001 ～35 – 40 GPa. Two meteorites, lherzolitic shergottite Y-793605 and orthopyroxenite ALH84001, are monomict breccias, indicating a two-phase shock history in toto: monomict brecciation at depth in a first impact and later shock metamorphism in a second impact, probably the ejection event. Crystallization ages of shergottites show only two pronounced groups designated S₁ (～175 Myr), including 4 of 6 dated basalts and all 3 lherzolites, and S₂ (330 – 475 Myr), including two basaltic shergottites and probably a third according to preliminary data. Ejection ages of shergottites, defined as the sum of their cosmic ray exposure ages and their terrestrial residence ages, range from the oldest (～20 Myr) to the youngest (～0.7 Myr) values for Martian meteorites. Five groups are distinguished and designated S_Dho (one basalt, ～20 Myr), S_L (two lherzolites of overlapping ejection ages, 3.94 ± 0.40 Myr and 4.70 ± 0.50 Myr), S (four basalts and one lherzolite, ～2.7 – 3.1 Myr), S_DaG (two basalts, ～1.25 Myr), and S_E (the youngest basalt, 0.73 ± 0.15 Myr). Consequently, crystallization age group S₁ includes ejection age groups S_L, S_E and 4 of the 5 members of S, whereas S₂ includes the remaining member of S and one of the two members of S_DaG. Shock effects are different for basalts and lherzolites in group S/S₁. Similarities to the dated meteorite DaG476 suggest that the two shergottites that are not dated yet belong to group S₂. Whether or not S₂ is a single group is unclear at present. If crystallization age group S₁ represents a single ejection event, pre-exposure on the Martian surface is required to account for ejection ages of S_L that are greater than ejection ages of S, whereas secondary breakup in space is required to account for ejection ages of S_E less than those of S. Because one member of crystallization age group S₂ belongs to ejection group S, the maximum number of shergottite ejection events is 6, whereas the minimum number is 2. Crystallization ages of nakhlites and Chassigny are concordant at ～1.3 Gyr. These meteorites also have concordant ejection ages, i.e., they were ejected together in a single event (NC). Shock effects vary within group NC between the nakhlites and Chassigny. The orthopyroxenite ALH84001 is characterized by the oldest crystallization age of ～4.5 Gyr. Its secondary carbonates are ～3.9 Gyr old, an age corresponding to the time of Ar-outgassing from silicates. Carbonate formation appears to have coincided with impact metamorphism, either directly, or indirectly, perhaps via precipitation from a transient impact crater lake. The crystallization age and the ejection age of ALH84001, the second oldest ejection age at 15.0 ± 0.8 Myr, give evidence for another ejection event (O). Consequently, the total number of ejection events for the 16 Martian meteorites lies in the range 4 – 8. The Martian meteorites indicate that Martian magmatism has been active over most of Martian geologic history, in agreement with the inferred very young ages of flood basalt flows observed in Elysium and Amazonis Planitia with the Mars Orbital Camera (MOC) on the Mars Global Surveyor (MGS). The provenance of the youngest meteorites must be found among the youngest volcanic surfaces on Mars, i.e., in the Tharsis, Amazonis, and Elysium regions.     

纤维夹角和铣削参数对CFRP铣削力的影响

为探索CFRP铣削加工中出现的分层、崩边等表面缺陷形成机理,对CFRP进行铣削加工实验。基于单因素实验法获得了纤维夹角对CFRP铣削力的影响规律,基于中心复合曲面设计,获得了硬质合金刀具铣削CFRP过程中铣削速度、每齿进给量和铣削深度对铣削力的影响规律,并构建了铣削力的预报模型。实验结果表明:纤维夹角在0°～90°,铣削力随纤维夹角的增大而降低,而在90°～180°,铣削力随纤维夹角的增大而增大。f_z和a_e对三个方向铣削力影响都较为显著。v_c对y向和z向铣削力影响较为显著,而对x向铣削力影响不显著。铣削力随三个铣削参数的升高而增大,其中每齿进给量对铣削力影响最大。