共查询到19条相似文献,搜索用时 140 毫秒
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In order to improve the deposition rate and microstructure of pyrocarbon, nickel was introduced by electroplating on carbon fibers and used as a catalyst during the deposition of pyrocarbon at 1000 C using methane as a precursor gas. The distribution of nickel catalyst and the microstructure of pyrocarbon were characterized by scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and Raman micro-spectrometry. Results show that nano-sized nickel particles could be well distributed on carbon fibers and the pyrocarbon deposited catalytically had a smaller d002 value and a higher graphitization degree compared with that without catalyst. In addition, the deposition rate of pyrocarbon in each hour was measured.The deposition rate of pyrocarbon in the first hour was more than 10 times when carbon cloth substrates were doped with nickel catalysts as compared to the pure carbon cloths. The pyrocarbon gained by rapid deposition may include two parts, which are generation directly on the nickel catalyst and formation with the carbon nanofibers as crystal nucleus. 相似文献
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The flow and heat transfer characteristics were numerically investigated on a film cooling model under different rotating operating conditions.The computational model was originated from the mid-span section of a typical turbine rotor with two rows of 14 staggered injection holes angled 30° both on the suction surface and pressure surface,and the flow through the coolant plenum and all the hole-pipes were resolved as a part of the computational domain by specifying the coolant mass flux in the plenum.The computations primarily focus on under-standing the rotational effect on film cooling performance in mechanism research approach.In the present study,the Reynolds number(Re) based on mainstream velocity and injection hole diameter varied from 1835.5 to 5507.4,and the averaged blowing ratio(M) ranges of 0.5 to 1.5.Results show that the coolant will move on to the high-radius locations near the suction and pressure surfaces due to the strong centrifugal effect,which leads to the decrease in adiabatic effectiveness accordingly.The discharge coefficients(Cd),on the pressure surface,are much higher than that on the suction surface under a given operating condition.In addition,the critical values of angular speed which represent the equilibrium of centrifugal force and Coriolis force near the pressure surface are also presented. 相似文献
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《中国航空学报》2015,(4)
A three-part numerical investigation has been conducted in order to identify the flow separation behavior––the progression of the shock structure, the flow separation pattern with an increase in the nozzle pressure ratio(NPR), the prediction of the separation data on the nozzle wall,and the influence of the gas density effect on the flow separation behavior are included.The computational results reveal that the annular conical aerospike nozzle is dominated by shock/shock and shock/boundary layer interactions at all calculated NPRs, and the shock physics and associated flow separation behavior are quite complex.An abnormal flow separation behavior as well as a transition process from no flow separation at highly over-expanded conditions to a restricted shock separation and finally to a free shock separation even at the deign condition can be observed.The complex shock physics has further influence on the separation data on both the spike and cowl walls, and separation criteria suggested by literatures developed from separation data in conical or bell-type rocket nozzles fail at the prediction of flow separation behavior in the present asymmetric supersonic nozzle.Correlation of flow separation with the gas density is distinct for highly overexpanded conditions.Decreasing the gas density or reducing mass flow results in a smaller adverse pressure gradient across the separation shock or a weaker shock system, and this is strongly coupled with the flow separation behavior.The computational results agree well with the experimental data in both shock physics and static wall pressure distribution at the specific NPRs, indicating that the computational methodology here is advisable to accurately predict the flow physics. 相似文献
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To reveal the radical recombination process in the scramjet nozzle flow and study the effects of various factors of the recombination, weighted essentially non-oscillatory(WENO)schemes are applied to solve the decoupled two-dimensional Euler equations with chemical reactions to simulate the hydrocarbon-fueled scramjet nozzle flow. The accuracy of the numerical method is verified with the measurements obtained by a shock tunnel experiment. The overall model length is nearly 0.5 m, with inlet static temperatures ranging from 2000 K to 3000 K, inlet static pressures ranging from 75 k Pa to 175 k Pa, and inlet Mach numbers of 2.0 ± 0.4 are involved.The fraction Damkohler number is defined as functions of static temperature and pressure to analyze the radical recombination progresses. Preliminary results indicate that the energy releasing process depends on different chemical reaction processes and species group contributions. In hydrocarbon-fueled scramjet nozzle flow, reactions with H have the greatest contribution during the chemical equilibrium shift. The contrast and analysis of the simulation results show that the radical recombination processes influenced by inflow conditions and nozzle scales are consistent with Damkohler numbers and potential dissociation energy release. The increase of inlet static temperature improves both of them, thus making the chemical non-equilibrium effects on the nozzle performance more significant. While the increase of inlet static pressure improves the former one and reduces the latter, it exerts little influence on the chemical non-equilibrium effects. 相似文献
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Flow field design and process stability in electrochemical machining of diamond holes 总被引:2,自引:1,他引:1
《中国航空学报》2016,(6):1830-1839
The metal grille, commonly composed of an amount of diamond holes, has been grow-ingly used as a key structure on stealth aircraft. Electrochemical machining (ECM) promises to be increasingly applied in aircraft manufacturing on the condition that process stability is guaranteed. In this work, a flow field model was designed to improve the process stability. This model is endowed with a variety of flow channel features, together with vibrating feeding modes. The flow field distribution on the bottom surface of the diamond hole was discussed and evaluated as well. The numerical results show that a short arc flow channel could significantly enhance the uniformity of electrolyte velocity distribution and a vibrating feeding of the cathode enables to reduce both fluctuations of the electrolyte velocity and pressure on the bottom surface of the diamond hole. Consequently, the flow field mutations were eliminated. It is verified from the experimental results that a short arc flow channel, when combined with vibrating feeding, is capable of improving machining localization and process stability markedly. What is more, the side gap on the bottom surface of the diamond hole could also be reduced by the abovementioned approach. 相似文献
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Numerical simulations of flow and heat transfer to supercritical RP-3 through the inclined tubes have been performed using LS k–e model embedded in Fluent. The physical properties of RP-3 were obtained using the generalized corresponding state laws based on the fourcomponent surrogate model. Mass flow rate is 0.3 g/s, system pressure is 3 MPa, inlet temperature is 373 K. Inclination of the inclined pipe varied from -90° to 90°, with heat flux varied from 300 k W/m~2 to 400 kW/m~2. Comparison between the calculated result and the experimental data indicates the range of error reasonable. The results of ±45° show that temperature inhomogeneity in inclined pipe produce the secondary flow in its cross section due to the buoyancy force. Depending on the strength of the temperature inhomogeneity, there will be two different forms of secondary flow and both contribute to the convective heat transfer in the pipe. The secondary flow intensity decreases when the inhomogeneity alleviates and thermal acceleration will play a leading role. It will have a greater impact on the turbulent flow to affect the convective heat transfer in the pipe. When changing the inclination, it affects the magnitude of the buoyant component in flow direction. The angle increases, the buoyancy component decreases. And the peak temperature of wall dominated by the secondary flow will move forward and increase in height. 相似文献
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LI Huan-yong JIE Wan-qi ZHAO Hai-tao 《中国航空学报》2006,19(B12):91-95
With diethylamine as a solvent, ZnSe films were formed on the Si substrate directly from zinc and selenium through the modified solvothermal method. The effects of holding temperature, deposition time and substrate surface treatment on the quality and morphologies of the ZnSe films were investigated. The growth mechanism of ZnSe films was proved to be a layer-nucleation growth process, which was tied in with the Stranski-Krastanov (SK) model. ZnSe films were identified by the X-ray diffraction pattern (XRD), the scanning electron microscope (SEM), the X-ray photoelectron spectroscope (XPS) and the photoluminescence (PL) techniques. The results indicate that the modified solvothermal method with diethylamine as a solvent is suitable to prepare high quality ZnSe films. 相似文献
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LI Huan-yong* JIE Wan-qi ZHAO Hai-tao College of Materials Science Engineering Northwestern Polytechnical University Xi'an China 《中国航空学报》2006,19(Z1)
With diethylamine as a solvent, ZnSe films were formed on the Si substrate directly from zinc and selenium through the modified solvothermal method. The effects of holding temperature, deposition time and substrate surface treatment on the quality and morpholo-gies of the ZnSe films were investigated. The growth mechanism of ZnSe films was proved to be a layer-nucleation growth process, which was tied in with the Stranski-Krastanov (SK) model. ZnSe films were identified by the X-ray diffraction pattern (XRD), the scan-ning electron microscope (SEM), the X-ray photoelectron spectroscope (XPS) and the photoluminescence (PL) techniques. The results indicate that the modified solvothermal method with diethylamine as a solvent is suitable to prepare high quality ZnSe films. 相似文献
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Pressure sensing and schlieren imaging with high resolution and sensitivity are applied to the study of the interaction of single-pulse laser energy with bow shock at Mach 5. An Nd:YAG laser operated at 1.06 lm, 100 mJ pulse energy is used to break down the hypersonic flow in a shock tunnel. Three-dimensional Navier–Stokes equations are solved with an upwind scheme to simulate the interaction. The pressure at the stagnation point on the blunt body is measured and calculated to examine the pressure variation during the interaction. Schlieren imaging is used in conjunction with the calculated density gradients to examine the process of the interaction. The results show that the experimental pressure at the stagnation point on the blunt body and schlieren imaging fit well with the simulation. The pressure at the stagnation point on the blunt body will increase when the transmission shock approaches the blunt body and decrease with the formation of the rarefied wave. Bow shock is deformed during the interaction. Quasi-stationary waves are formed by high rate laser energy deposition to control the bow shock. The pressure and temperature at the stagnation point on the blunt body and the wave drag are reduced to 50%, 75% and 81% respectively according to the simulation. Schlieren imaging has provided important information for the investigation of the mechanism of the interaction. 相似文献
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利用化学气相浸渗法制备了 C/ Si C复合材料 ,研究了两种加热方式 (电阻加热和中频感应加热 )下 Si C沉积物形貌、沉积机制以及复合材料结构和性能。结果表明 :电阻加热时沉积单元为高温熔滴 ,Si C沉积物为卵石形貌 ;感应加热时沉积单元为 Si C固体粒子 ,Si C沉积物为粒状形貌。电阻加热时高温熔滴易于渗入纤维束内部 ,复合材料结构均匀 ,致密度高 ;而感应加热时 Si C固体粒子多以团聚体的形式沉积在纤维束表面 ,难于渗入纤维束内部 ,复合材料结构均匀性差 ,难以致密。沉积机制的差异导致两种复合材料的结构差异 ,使得复合材料的力学性能不同 ,电阻加热时复合材料弯曲强度、断裂韧性和断裂功较高 ;感应加热时复合材料性能较低 相似文献
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基体改性C/C复合材料在高温下的热膨胀规律 总被引:1,自引:0,他引:1
对基体改性前后C/ C 复合材料在高温下的热膨胀系数随温度的变化规律进行了研究。结果表明,基体改性前C/ C 复合材料在高温下的热膨胀系数随温度的变化完全符合碳素材料的一般线性变化规律,而基体改性后C/ C 复合材料在高温下热膨胀系数随温度的变化在900 ℃以前为线性关系,在900~1500 ℃之间为指数关系。通过数学推导与实验验证,证实了这种关系的合理性与可靠性,这对于改善C/ C 复合材料与其抗氧化涂层之间热膨胀系数的匹配程度,全面提高C/ C 复合材料的高温抗氧化性具有一定的指导意义。 相似文献
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采用"化学气相渗透+先驱体浸渍裂解"(CVI+PIP)混合工艺制备固体冲压发动机用C/C-SiC复合材料喷管内层,综合考查复合材料的微观结构、弯曲性能和抗烧蚀性能以及固冲发动机C/C-SiC喷管内层水压和点火实验。结果表明:复合材料的弯曲强度达到197 MPa,且断裂破坏行为呈现典型的韧性模式;复合材料具有优异的抗氧化烧蚀性能,氧化烧蚀200 s后线烧蚀率仅为0.0063 mm·s-1;研制的C/C-SiC复合材料构件的水压爆破压强为6.5 MPa,表明构件具有良好的整体承载能力;C/C-SiC复合材料喷管内层高温综合性能通过了固体冲压发动机点火实验考核。 相似文献
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俞继军%马志强%姜贵庆%童秉纲 《宇航材料工艺》2003,33(1):36-39
对C/C复合材料试件的表面细观烧蚀进行了常压下的亚、超声速和高压下的亚音速烧蚀形貌的测量;根据测量结果,分析了C/C复合材料在上述情况下的质量损失规律。结果表明:C/C复合材料在亚音速流场的条件下,z向纤维束首先发生剥蚀,当压力升高时,碳布会发生层间剥蚀的现象;而在超音速条件下,碳布更容易发生剥蚀的现象。 相似文献
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通过CVI+PIP 制备了准三维针刺C/ C-SiC 薄壁喉衬,预制体碳布铺层方式分别采用与喉衬内型
面形状相同的仿形铺层以及与喉衬入口端角度相同30°铺层。研究了两种铺层方式对最终构件层间弯曲性
能、整体承压性能以及抗烧蚀抗冲刷的影响。结果表明,构件的弯曲强度分别为205 和152 MPa;水压爆破压
力分别为6. 5 和4. 9 MPa。用与材料表面夹角为30°的氧乙炔气流考查材料的抗烧蚀及冲刷性能,同角度铺层
成型材料抗冲刷能力明显较好,200 s 其线烧蚀率为仿形铺层成型材料的70%。 相似文献