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1.
Choking phenomena of sonic nozzles at low Reynolds numbers   总被引:3,自引:0,他引:3  
The choking phenomena of sonic nozzles were investigated for the Reynolds number range from 40 to 30 000 for nitrogen gas. The results showed that the critical back pressure ratio is a function of the Reynolds number only, with different characteristics for different nozzle shapes. In ISO-type toroidal-throat Venturi nozzles, the minimum Reynolds number satisfying the choking condition is about 40 and the critical back pressure ratio is only about 0.05 at this minimum Reynolds number. It was also found that the critical back pressure ratio has a local minimum value around Reth=4000 and that the local maximum value is around Reth=10 000 due to the change in characteristics of the boundary layer in the diffuser. On the other hand, the critical back pressure ratio in quadrant nozzles decreases monotonically with decreasing Reynolds number, unlike the former nozzle, and the minimum Reynolds number necessary for choking is estimated to be approximately the same as that in the Venturi nozzle.  相似文献
2.
一种气体流量的软测量系统研究   总被引:3,自引:1,他引:2  
流量信号是生产过程中一个重要参数。虚拟仪器技术是仪器仪表领域一个充满活力的发展方向。从光滑圆管的3种紊流流速分布模型出发,应用虚拟仪器技术,实现了使用管道截面上的最大流速来测量气体流量的软测量方法。详细阐述了该方法的测量原理、系统构成及特点,体现了在流量测量领域的先进技术和最新方法。实验数据表明了这种方法是准确、可靠的,能够实现在线、自动测量并具有节能的效果,具有较好的应用前景。  相似文献
3.
为研究FWS-9发动机作为高空无人飞行平台动力装置的可行性,在对发动机旋转部件(压气机、涡轮)雷诺数修正的基础上,研究了高空、低速、低雷诺数对发动机部件(风扇、压气机、主燃烧室和涡轮)和整机性能、稳定性的影响规律.  相似文献
4.
低雷诺数音速喷嘴临界背压比的实验研究   总被引:1,自引:1,他引:0  
音速喷嘴是气体流量标准装置中最常用的标准流量计,喷嘴临界背压比直接关系到装置的准确度,喉部雷诺数低于2×105的喷嘴需要进行临界背压比测试。建立了一套基于喷嘴串联方法的临界背压比测试系统,将不易准确测量的质量流量转换为较易准确测量的压力,实现了临界背压比的准确高效测量。研究表明,低喉部雷诺数喷嘴临界背压比小于其设计值,且喉部雷诺数越小,临界背压比越低;另外可能出现一种"非临界状态提前"现象,引起临界背压比的进一步降低,且降低程度与喷嘴加工水平有关,更加说明了临界背压比测试的必要性。  相似文献
5.
Spanwise flexibility is a key factor influencing propulsion performance of pectoral foils.Performances of bionic fish with oscillating pectoral foils can be enhanced by properly selecting the spanwise flexibility.The influence law of spanwise flexibility on thrust generation and propulsion efficiency of a rectangular hydro-foil is discussed.Series foils constructed by the two-component silicon rubber are developed.NACA0015 shape of chordwise cross-section is employed.The foils are strengthened by fin rays of different rigidity to realize variant spanwise rigidity and almost the same chordwise flexibility.Experiments on a towing platform developed are carried out at low Reynolds numbers of 10 000,15 000,and 20 000 and Strouhal numbers from 0.1 to 1.The following experimental results are achieved: (1) The average forward thrust increases with the St number increased;(2) Certain degree of spanwise flexibility is beneficial to the forward thrust generation,but the thrust gap is not large for the fins of different spanwise rigidity;(3) The fin of the maximal spanwise flexibility owns the highest propulsion efficiency;(4) Effect of the Reynolds number on the propulsion efficiency is significant.The experimental results can be utilized as a reference in deciding the spanwise flexibility of bionic pectoral fins in designing of robotic fish prototype propelled by flapping-wing.  相似文献
6.
雷诺数对风力机专用翼型气动性能影响的研究   总被引:1,自引:0,他引:1  
雷诺数是影响翼型气动特性的主要参数之一,当雷诺数在5×10~5~1×10~7范围内变化时,基于N-S控制方程,对S827翼型在攻角α为-14°~45°范围内变化时的气动特性进行数值计算,研究了雷诺数对该翼型的升力特性、阻力特性、最大升力系数、最大升阻比、流动分离特性、失速特性等气动特性的影响.  相似文献
7.
Analysis of low Reynolds number flow around a heated circular cylinder   总被引:1,自引:0,他引:1  
The objective of this study is to investigate the forced convection from and the flow around a heated cylinder. Experimental and computational results are presented for laminar flow around a heated circular cylinder with a diameter of 10 mm. The experiments were carried out using Particle Image Velocimetry (PIV) in a wind tunnel, and numerical simulations using an in-house code and a commercial software package, FLUENT. This paper presents comparisons for vorticity and temperature contours in the wake of the cylinder. Experimental and computational results are compared with those available in the literature for heated and unheated cylinders. An equation is suggested for a temperature-dependent coefficient defining a reference temperature to be used in place of the constant used in other studies. An attempt is also made to correct differences between average cylinder surface temperature and measured interior temperature of the cylinder. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. László Baranyi received his MEng degree from the Technical University for Heavy Industry, Hungary, in 1975 and his PhD in 1990. He worked as an associate professor at Nagaoka University of Technology, Japan, from 1995 to 1997. Dr. Baranyi is currently an associate professor at the University of Miskolc, Hungary. He serves as an editor of the Journal of Computational and Applied Mechanics. His research interests include bluff body aerodynamics and fluid-structure interaction. Szilárd Szabó, PhD (1995, University of Miskolc), professor, head of Department of Fluid and Heat Engineering University of Miskolc, Hungary. He earned his MSc degree in mechanical engineering in 1975 from the Technical University for Heavy Industry. He serves as an editor of the Journal of Computational and Applied Mechanics and a deputy editor-in-chief of the Hungarian journal GéP. Dr. Szabó’s research fields are supersonic gas ejectors, turbomachines, CFD, power engineering. Betti Bolló, assistant at the Department of Fluid and Heat Engineering, University of Miskolc, Hungary. She received her MSc degree from the University of Miskolc in Information Engineering (Systems of Power Engineering) in 2003. Ms Bolló’s research interests include CFD and internal combustion engines. Róbert Bordás, PhD student at the Laboratory of Fluid Dynamics and Technical Flows, University of Magdeburg “Ottovon-Guericke” in Germany. He received his MSc degree from the Budapest University of Tech-nology in Integrated Engineering (Faculty of Mechanical Engineering) in 2005. His research interests include optical measurements in engineering flows.  相似文献
8.
Computational fluid dynamics(CFD) simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 pm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.  相似文献
9.
圆盘止推静压气体轴承亚音速流场的简化计算   总被引:1,自引:1,他引:0  
雷诺气体润滑方程仅涉及轴承气膜内的静压分布,对静压气体轴承流道特性的准确刻画还需要研究轴承流道内的气流速度场。将忽略惯性力的纯粘性等温气膜和等熵流动的供气孔拼接,建立了单供气孔环面节流圆盘止推轴承的流道简化模型,给出流道各部分气流马赫数、雷诺数和压力分布的计算公式。结果表明,气膜中气流速度随矢径变化的性质,取决于速度梯度为零的矢径位置;气膜中的气流雷诺数随矢径的增加不断减小。实际的计算结果表明,只要气膜入口截面上的气流马赫数小于临界声速,整个轴承流道将工作在亚音速,供气压力或气膜高度的变化对气膜起始区域边界层发展段长度的影响很小,供气孔始末端截面上压力和温度的变化也很小,忽略惯性力的纯粘性等温雷诺模型基本能够适用轴承的整个亚音速工况。气膜起始区域边界层发展段的长度,可以用气膜中雷诺数大于临界雷诺数的区域长度来近似。  相似文献
10.
Influence of oil film inertia forces on thermo-elasto-hydrodynamic lubrication performances of a piston skirt is analyzed, based on a proposed Reynolds lubrication equation for the consideration of oil film inertia force effects. Further, a scheme to solve the inertia effects is given. The numerical results show that oil film inertia forces can result in increments in film pressure and temperature, hydrodynamic friction force and load capacity, deformation, and transverse displacements of the piston skirt. Moreover, the influences are obvious for a big reduced Reynolds number. Therefore, oil film inertia force effects on thermo-elasto-hydrodynamic lubrication performances of a piston skirt in a high speed internal combustion engine should be considered.  相似文献
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