共查询到20条相似文献,搜索用时 171 毫秒
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《机械工程材料》2015,(8)
基于局域热力学平衡假设,建立等离子喷涂射流的三维非稳态湍流模型,运用计算流体力学软件ANSYS CFX模拟了氩/氢等离子喷涂过程中等离子特性分布以及喷枪内部场变化对射流形态的影响,并与高速摄像机的拍摄结果进行了对比。结果表明:模拟得到的射流波动明显,其形态与试验得到的结果吻合较好;喷枪内与射流域等离子体特性分布表现出明显的三维特征,其中速度分布的三维特征较之温度的更加明显;射流射入大气中后,温度和速度均沿轴向衰减,随着射流发展,与冷空气的卷吸作用愈明显,等离子体与冷空气之间能量和动量交换愈剧烈,大约距离喷枪出口27.4mm处其温度和速度的衰减加剧;射流域速度分布较之温度分布受空气影响更大。 相似文献
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通过对射流图像的采集和处理,研究了气体流量、工作电流对射流温度场分布的影响。根据射流与粉末动量传递和能量耦合关系,建立粉末飞行特性模型,研究不同粉末在射流中的飞行时间,分析粒子飞行的温度特性和速度特性对熔射成形质量的影响。利用双比色原理对粉末飞行模型进行的实验验证表明:模拟结果与实验结果基本吻合,建立的粉末飞行特性模型对单粒子在射流中的飞行特性和动量/能量耦合规律的研究具有重要的意义。 相似文献
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针对水气两相射流泵传能效率较低,吸气残压过大的问题,结合环形射流和自激振荡射流的优点,提出环形水气自激振荡脉冲射流的概念。以环形射流理论为基础,推导了混合相界面上的连续性方程和动量方程。采用Realizable k-ε紊流模型和欧拉多相流模型对环形水气自激振荡脉冲射流流场分别进行了定常和非定常数值模拟。计算了环形水气自激振荡射流泵的流量比q、压力比h和效率η等性能参数。对下喷嘴处的流体平均速度进行了非定常模拟计算。对下喷嘴处混合相瞬时速度脉冲进行了频率分析。与普通环形水气射流相比,环形自激振荡射流对气体的卷吸作用能力得到增强,且下喷嘴处的混合相瞬时速度值具有显著的脉冲主频。 相似文献
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大功率激光焊接光致等离子体的光谱分析 总被引:5,自引:0,他引:5
大功率激光焊接过程中,光致等离子体的粒子密度及温度对入射激光能量的传输效率及焊缝的熔深都有很大影响。采用光谱诊断、分析方法,利用谱线相对强度法对激光光致等离子体的温度及电子密度进行了测量与计算,给出了实验条件下光致等离子体电子密度与激光焊接能量及焊接熔深的量化关系。 相似文献
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为了更加真实地分析风机流场,并缩短数值计算时间,分别建立不同参数(尺寸、转速)的轴流风机的三维流场模型,基于RANS模型中的Realizable k-ε模型,分别采用速度边界、Fan边界、3D Fan zone 3种边界条件对风机内部流场、射流通风流场进行稳态计算,并将计算结果与文献中风机试验数据进行了对比验证。为了进一步验证风机内部流场模拟结果的准确性,对1台SF3-4轴流式风机进行性能测试,结果表明:采用3D Fan zone和Fan边界条件计算内部流场的气动性能数据与试验值最接近,平均误差分别为1.59%和4.42%,但要求的网格数较多,计算时间长,而采用速度边界条件虽平均误差为10.3%,要求的网格数较少且计算时间短。在模拟风机射流通风流场时,采用3D Fan zone与Fan边界条件能实现流场边缘处的微小尺度旋流及流场各处的温度变化,而采用速度边界条件虽能实现流场中心处的大尺度射流,但无法实现流场其他位置的流动、传热现象;3种边界条件的计算结果都与风机内部流场的实际性能参数吻合度高,研究结果可为风机流场研究提供参考。 相似文献
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射流形态是熔射过程中最直观的射流信息,它是熔射各工艺参数稳定与否的直接反映。本文提出基于CCD对氩氮等离子熔射射流进行图像采集,利用数字图像处理方法提取射流形态,以射流狭长度来描述射流形态特征的识别方法。实验研究结果表明:射流狭长度特征可以很好地反映不同工艺条件下射流的形态特点;通过实验分析主要工艺参数对该特征的影响规律,得到输入电压对该特征有主要影响的结果;结合相应工艺条件下粒子飞行行为检测实验结果,对该射流诊断系统进行验证,表明该系统可实际应用于RSTP的工艺分析中。 相似文献
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钛合金是一种典型的难加工材料,其热传导率低,切削过程温升大而易加剧刀具磨损。本文通过对TC4钛合金的车削试验,研究了在干切削和复合喷雾冷却条件下切削温度随切削速度、切削深度和进给量的变化情况。结果表明:切削温度随着切削速度、切削深度和进给量的增大而增大;采用复合喷雾冷却技术可在TC4钛合金车削过程中取得较好的冷却效果,切削温度明显低于干切削条件下的切削温度。 相似文献
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Mohammad Amin Baghchesara Hossein Abdizadeh 《Journal of Mechanical Science and Technology》2012,26(2):367-372
In this research, aluminum alloy (A356.1) matrix composites reinforced with 1.5, 2.5 and 5 Vol.% nanoscale MgO particles were
fabricated via powder metallurgy method. Pure atomized aluminum powder with an average particle size of 1μm and MgO particulate
with an average particle size between 60 to 80 nm were used. The specimens were pressed by Cold Isostatic Press machine (CIP),
and were subsequently sintered at various sintering temperatures, viz. 575, 600 and 625°C. Optimum amount of reinforcement
and sintering temperature were determined by evaluating the density, microstructure and mechanical properties of composites.
The composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Hardness and compression
tests were carried out in order to identify mechanical properties. Reinforcing the Al matrix alloy with MgO particles improved
the hardness and compressive strength of the alloy to a maximum value of 44 BHN and 288 MPa, respectively. The most improved
compressive strength was obtained with the specimen including 2.5% of MgO sintered at 625°C. According to the experiments,
a sintering temperature of 625°C showed better results than other temperatures. A good distribution of the dispersed MgO particulates
in the matrix alloy was achieved. 相似文献
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采用热压烧结法制备了三种不同成分的SiC颗粒增强镁-锌-锆基复合材料,使用LMR-1型低频力学弛豫谱测试系统研究了铸态镁-锌-锆合金及热压烧结SiCp/镁-锌-锆基复合材料的阻尼性能随频率和温度的变化关系.结果表明:SiC颗粒的加入使复合材料的阻尼性能比基体合金有显著提高;另外随着合金中锌含量的增加,复合材料的内耗值不断下降;在频率为3×10-3~7Hz范围内,基体合金及复合材料的内耗值均随着频率的增加先快速减小随后又逐渐增大;在本试验条件下SiCp/Mg-0.93%Zn-0.70%Zr基复合材料的内耗值最大,该复合材料在50~100℃的温度范围内出现弛豫内耗峰. 相似文献
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《Wear》1996,193(2):169-179
The influence of temperature on wear resistance was studied in a 2618 Al alloy reinforced with 15 vol% SiC particulates and the corresponding unreinforced alloy in the temperature range 20–200 °C. A transition from mild to severe wear (shown by an increase of two orders of magnitude in the wear rates) was observed in both materials beyond a critical temperature. The addition of the SiC particulates improved the wear resistance by a factor of two in the mild wear region, and the transition temperature, which was around 50 °C higher in the composite. This higher transition temperature was due to the retention of the mechanical properties in the composite at elevated temperature. Heat treatments (either natural or artificial aging) did not modify substantially the wear resistance of either the composite or the unreinforced alloy. 相似文献
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Tiwari N Sahasrabudhe SN Tak AK Barve DN Das AK 《The Review of scientific instruments》2012,83(2):025110
A high speed camera has been used to record and analyze the evolution as well as particle behavior in a single wire arc plasma spray torch. Commercially available systems (spray watch, DPV 2000, etc.) focus onto a small area in the spray jet. They are not designed for tracking a single particle from the torch to the substrate. Using high speed camera, individual particles were tracked and their velocities were measured at various distances from the spray torch. Particle velocity information at different distances from the nozzle of the torch is very important to decide correct substrate position for the good quality of coating. The analysis of the images has revealed the details of the process of arc attachment to wire, melting of the wire, and detachment of the molten mass from the tip. Images of the wire and the arc have been recorded for different wire feed rates, gas flow rates, and torch powers, to determine compatible wire feed rates. High speed imaging of particle trajectories has been used for particle velocity determination using time of flight method. It was observed that the ripple in the power supply of the torch leads to large variation of instantaneous power fed to the torch. This affects the velocity of the spray particles generated at different times within one cycle of the ripple. It is shown that the velocity of a spray particle depends on the instantaneous torch power at the time of its generation. This correlation was established by experimental evidence in this paper. Once the particles leave the plasma jet, their forward speeds were found to be more or less invariant beyond 40 mm up to 500 mm from the nozzle exit. 相似文献
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为使易熔合金引信可靠延期解除保险以保证弹道安全,需要根据弹丸速度确定在安全时间和距离内引信易熔合金的熔点。以瑞士厄利空2ZLa/353式35 mm 双管自行高射炮爆破燃烧榴弹 KZVD 引信为例,从工程的角度出发,简化了外弹道,在初始弹速为1175 m/s 和误差范围为±15 m/s 的条件下,采用气动加热理论对榴弹外弹道起始阶段弹头驻点的温度进行了理论建模计算和仿真验证,通过分析相应弹速下的弹头驻点温度确定出满足安全距离要求的易熔合金熔点温度。仿真结果表明,理论计算与仿真试验确定出1160-1190 m/s 初始弹速范围内的易熔合金熔点温度的结果一致,因此可以利用该热力学模型并根据弹道安全要求来设计相应熔点的易熔合金引信,所用方法可以为高速飞行弹体的热力学研究提供参考。 相似文献