Experimental determination of errors in piston manometers at high pressures

Conclusions The suggested method of comparing piston manometers of high pressures by means of a differential instrument is also applicable for determining experimentally the differences between the errors as functions of pressure. The experiments carried out up to pressures of 7000 kg/cm² confirmed the previously obtained formulas of corrections for strains in manometers with different piston systems.     

Influence of cylinder compression methods on the deformation of the piston pair of a high-pressure manometer

The influence of methods of compression of high-pressure cylinders on the deformation of a piston pair as well as the effect of pressure on the flanks of steel and hard-alloy cylinders are considered. The magnitudes of the deformation of the cylinder channels are preented and the influence of the pressure exerted on the cylinder flanks on the effective area of high-pressure piston pairs is given.     

Deviation of deformation of piston and cylinder of high-pressure piston pair from deformation as calculated with the use of a solution of the Lamé problem

The deviations of the deformation of a piston and cylinder from the deformation as calculated from formulas in the solution of the Lamé problem as well as the influence of the pressure distribution in the working channel of a piston pair on these deviations are considered. Conclusions regarding certain aspects of the design of high-pressure piston pairs are presented.     

Increasing the Accuracy of Reproduction of Pressure by Means of the Ukrainian Secondary Standard of the Unit of Pressure

The estimated components of the error in the determination of the effective area of a measuring piston-cylinder assembly of a piston manometer with a non-sealed piston are reported. Such manometers are incorporated into the secondary standard of the unit of pressure.     

Pneumatic-driven piston acceleration in a barrel

The regime of pneumatic acceleration of a piston in a barrel up to a transonic velocity has been studied. The results are obtained by numerical solution of a system of nonstationary equations for a narrow channel, which have been integrated to within the second order of accuracy with respect to temporal and spatial variables. Quantitative estimates are obtained for the influence of various factors on the piston velocity, including wave processes, friction, heat exchange, and pressure in front of the moving piston. Some aspects of the formation of a nonstationary turbulent boundary layer at the barrel wall behind the piston are considered.     

Active piston technique to optimize the chamber pressure in two-stage light-gas guns

We report a study in the field of gun design and optimization, paying particular attention to the issue of energy matching between the pump tube and the barrel. The objective was to set up a technique in order to obtain a nearly constant pressure at the projectile base, without using a high-pressure tapered section in which the piston extrusion occurs. In a first step, it was analyzed the opportunity of using two separate pistons inside the pump tube, in which the back piston sustains the stroke of the first one for a longer time. Then, to cope with technological problems, the same idea was implemented by developing a single piston characterized by an active core. In the following, after having presented a general overview on the proposed technique, we describe the numerical model used for performance evaluation and a numerical comparison of the performance achievable with a single piston and with the proposed method. Finally, we report some experimental results that were used for the model validation and also for demonstrating the technological feasibility of an active-core free-piston for two-stage light-gas guns.     

恒压式径向柱塞泵定子的位移振动特性分析

恒压式径向柱塞泵的工作状态可分为恒流状态和恒压状态,而定子在这两个工作状态下表现出不同的振动频率特性.首先建立了径向柱塞泵定子的动力学模型,然后对其在两个状态下的位移振动频率特性进行分析,并设计振动测试装置对JB32H型径向柱塞泵定子的进行振动试验研究.分析及试验结果表明:无论在恒流状态还是在恒压状态,定子振动具有周期性;由于恒压控制系统的作用,恒压状态下的位移振动频带要比恒流状态下的位移振动频带窄;在恒压状态的频带范围内,恒流状态下的幅值要小于恒压状态下的幅值.研究的结果有助于柱塞泵的振动噪声控制.     

一种活塞式压力计的数值研究方法

基于ANSYS流固耦合仿真技术,提出了一种活塞式压力计的数值研究方法,以0~250 MPa压力测量范围的简单型活塞式压力计为例,验证了该方法的可行性,并计算和分析了不同平衡工作压力下活塞间隙流体压力分布与活塞有效面积的变化规律。这种活塞式压力计数值研究方法,能有效搭建和模拟简单型活塞式压力计的三维模型,为活塞式压力计的理论研究提供新的思路。     

测量线性压缩机活塞位移和PV功的新方法

提出利用激光三角法测量压缩机的活塞位移,结合压力传感器测得的气体压力,计算得到压缩机的活塞PV功;忽略活塞间隙的漏气损失,可计算得压缩机的输送PV功。设计了适用于激光测量活塞位移的带可视化窗口的压缩机外壳。针对一台特定压缩机,理论计算活塞与气缸之间的漏气量并通过实验验证了漏气量为小量。不同工况下对压缩机活塞位移进行测量,计算得到相应的活塞PV功和输送PV功,并与热线测量的输送PV功进行相互验证。利用激光测活塞位移的方法,观察脉冲管制冷机降温过程中压缩机活塞位移、压力、PV功及相位角的变化,给出相关分析。     

A manometer with an effective piston area unchanged by pressure

Summary Conditions under which the effective area of an unpacked piston of a manometer is independent of pressure were analyzed. An arrangement of a piston system with a piston area unchanged by pressure is suggested.     

活塞二阶运动对非道路高压共轨柴油机振动及噪声影响分析

活塞敲击是柴油机主要的振动和噪声源,其主要原因是活塞在其与缸套的间隙中做横向和偏摆的二阶运动,因此研究活塞设计参数对活塞二阶运动的影响,优化活塞动力学特性,对于发动机减振降噪具有重要意义。以某非道路四缸高压共轨柴油机为研究对象,建立活塞动力学计算模型以及整机多体动力学计算模型,通过机体和曲轴的模态试验,验证了有限元模型的准确性;采用正交设计方法,研究了活塞销偏置量、活塞裙部中凸点位置、配缸间隙对活塞动力学、整机振动与噪声的影响。研究结果表明:活塞配缸间隙对活塞敲击能量、活塞敲击力、活塞所受力矩影响最大;对发动机振动噪声敏感性分析显示,活塞销偏置是影响发动机振动与噪声性能的关键因素。     

Self-similar piston problem in non-ideal gas

Self-similar flows of a non-ideal gas driven by an expanding piston are studied. The equation of state for such gases is taken in the best suitable form that is found to be fairly accurate at low density region. The shock is assumed to be strong and propagating in a uniform medium at rest. The total energy of the flow between the shock and piston is assumed to be varying with shock radius obeying a power law. Both approximate analytical and numerical solutions are obtained for various values of the parameter that characterises the non-ideal nature of the gas. The influence of this parameter on not only the flow field but also on the shock density ratio, drag coefficient and pressure distribution on the piston surface is studied.     

The study of a reference loader-spring piston barometer

Conclusions Owing to their high precision and insensitivity to knocks and vibrations during transportation the piston instruments should find wide application for comparing with each other high-precision absolute stationary mercury barometers.Moreover, these barometers can be used for precision measurements of atmospheric pressure in various metrological and scientific research studies. With very stiff springs these barometers can measure microfluctuations of atmospheric pressure. With low-pressure springs the barometers provide the mean value of the atmospheric pressure.     

无油线性压缩机的频率特性和活塞偏移特性研究

针对线性压缩机随工况和热负荷变化而引起共振频率和活塞中心位置偏移量改变的问题,建立了关于压缩机共振频率的线性等效模型和傅里叶变换计算模型。两种模型用来预测线性压缩机的共振频率,后者同时用来计算活塞中心位置偏移量,模型中考虑了不同行程、不同排气压力对共振频率的影响以及不同行程、不同排气压力和不同运行频率对活塞中心位置偏移量的影响。为了验证模型的有效性,搭建了用来测量线性压缩机共振频率和活塞中心位置偏移量的测试系统,并将测量结果与模型所计算结果进行对比,结果表明,线性等效模型相比于傅里叶变换计算模型能更加准确的预测线性压缩机的共振频率;线性压缩机的共振频率随着行程的增加而逐渐减小,随着排气压力的增加而逐渐增加。实验表明,线性压缩机活塞中心位置偏移量随行程的增加而几乎不变,随着排气压力的增加而逐渐增加。傅里叶变换计算模型针对不同行程下活塞中心位置偏移量预测值高于实际值;但在不同排气压力或不同行程下的活塞偏移量可用该模型计算压缩机在上止点位置的偏移量来进行预测,误差不大于10%。     

基于ANSYS的柱塞副间隙自动补偿技术研究

柱塞和缸孔配合间隙的大小直接影响水液压柱塞泵的容积效率.利用工程塑料PEEK具有良好弹塑性和密封性的优势,提出了一种新型柱塞副间隙自动补偿结构,用于柱塞与缸孔之间的密封．通过ANSYS仿真软件,分析了不同宽度的环形槽在周期性变化的压力下,对应的柱塞套变形量．结果表明,该结构不仅能有效降低柱塞/缸孔副的泄漏,而且材料的应力幅值大为降低,能够很好地延长柱塞副的使用寿命．     

A simplified calculation model for the sliding contact boundaries in a hydrostatic piston mechanism

The objective of this study was to discuss simplified calculation models for the piston/cylinder sliding mechanism in which boundary contact partly occurs invariably. An efficient prediction of the boundary leakage and friction is often needed, such as in a swash-plate axial piston machine whose lubrication test is hard to perform due to the mechanism complexity. In order to model this physically uncertain lubrication regime, two calculation models were compared to compute the lubrication behaviors: “rigid boundary model”, whose theoretical concept was previously reported in the literature, and “elastic boundary model”, newly proposed in this study. Developed numerical algorithms commonly facilitated the simultaneous calculation of body motion and fluid film pressure to observe piston motion, reaction forces, and power loss. The results showed that simulations using the elastic boundary model should be more helpful for the prediction in the earlier development stage than the previous model since the methodology provides much less simulation time than full-order calculation, higher accuracy than the rigid model, and useful engineering parameters such as surface stress. The proposed calculation model can be extended to various asymmetrically loaded reciprocating piston mechanisms for efficiently predicting the lubrication behavior.     

The new method of traceability of a force-balanced piston gauge used as primary vacuum standard

The force-balanced piston gauge is a primary vacuum standard developed in the 1990s. The general principle of the instrument was first presented in Ooiwa A (Metrologia 30 (1994) 607). Non-rotating piston is connected to an electronic dynamometer and centered by means of transient gas flow in a double tapered gap between piston and cylinder. More details about it can be found in Delajoud, Girard(NCSL International Workshop and Symposium 2002; Vakuum Forschung Praxis 15 (2003) 24) and Tesar, Prazak(Vacuum 67 (2002) 307).Czech Metrology Institute developed its own method of the primary traceability of this instrument through the determination of its effective area. In this paper, there will be described experimental setup of this comparison as well as the experimental results from the traceability calibrations of the effective area in gauge and absolute mode using experimental method of hydrostatic comparison with the classical rotating piston balances and a digital non-rotating piston balance. It will, of course, include the uncertainty budget of this way of traceability and the final uncertainty of the pressure generation of the instrument.     

极端工况下的高压柱塞马达密封环摩擦特性

为减少极端工况下因密封环摩擦磨损导致的疲劳断裂,保证马达的容积效率和可靠性。以法向正压力和剪切应力线性表示密封环摩擦力,并通过模态分析法和有限体积法分别研究系统多体动力学与缸孔内流体动力学,计算不同主轴转角、不同宽径比和弧面锥角下密封环的法向正压力和壁面剪切应力。研究结果表明:改变主轴转角引起的排量变化对摩擦力的影响较小;而密封环结构参数的变化影响明显,当宽径比小于0.3和弧面锥角小于1.8°时,摩擦力随宽径比和锥角增大而减小,在宽径比为0.3,弧面锥角为1.8°时摩擦力达到最小,最大缩减率分别为28%和25%;但当宽径比大于0.3和弧面锥角大于1.8°时,摩擦力随宽径比和锥角增大而增大;另剪切应力随着宽径比增大而增大;而受弧面锥角影响较小。研究结果为柱塞马达密封环减摩设计提供理论基础和依据。     

Velocity correlations between a vibrated granular gas and a piston on top

The stationary state eventually reached by a vibrated granular gas with a piston on the top, and in presence of gravity, is considered. The relationship between the second velocity moments of the piston and of the gas just below it is investigated by using event driven molecular dynamics simulations. It is concluded that velocity correlations between the piston and the gas play a crucial role in determining the velocity fluctuations of the piston, that can be much larger than estimated by energy equipartition.     

Influence of the piston displacement profile on the performance of a refrigerating cycle equipped with an axial piston compressor

An extended analysis aiming to investigate the influence of the piston displacement in an axial compressor on the thermodynamic cycle of a refrigeration system was carried out. Axial piston compressors are commonly equipped with a rotating disk plate that guides the pistons along a sinusoidal displacement. A proper shape of the rotating disk can lead to a piston displacement that optimizes the power consumption and then the refrigeration cycle efficiency. In this paper, a sensitivity analysis on the compressor cycle characteristics by varying the piston displacement profile and the compressor operating conditions is presented. The mechanical analysis of the forces exerted by the piston on the rotating disk was also carried out to estimate the mechanical stresses acting on the rotating disk.