轴对称体空化水动力脉动特性的实验研究

为了研究轴对称体非定常空化的脉动特性,采用高速全流场显示技术和动态测力系统实验研究了绕半球型和平头轴对称体的非定常空化流场及其动力特性。实验在闭式水洞中进行,采用高速摄影的方法观察了在不同空化数下绕半球型和平头轴对称体的空穴形态,总结了在不同空化数下空泡形态的脉动特性;测量了轴对称体受到的阻力,并对阻力信号进行了时频分析,得到了轴对称体阻力在非定常空化阶段的时频特征。结果表明:空泡形态及其对应的动力特征随着空化数的变化存在明显的非定常特性,空化流场形态与动力特征频率存在高度的相关性。并且不同头型轴对称体的脉动特性存在明显的差异,半球型轴对称体空泡流动的脉动主要是空泡尾部的高频小脱落引起的,而平头轴对称体的空泡流脉动成分主要是大尺度的漩涡空泡团的周期性脱落,空化流场的低频特征频率与空泡的大断裂相对应。     

Connection between average and pulsation characteristics in turbulent flow of polymer solutions in a round tube

Results are given for measurements of the average and pulsation characteristics of dynamically stable turbulent flows of polymer solutions in a round tube. Experimental dependences are presented which indicate the presence of a close and unique connection between the turbulent pressures and shear stresses at the wall of the tube.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 6, pp. 1016–1022, December, 1973.     

The distribution of the velocities of doubly dispersed particles in a downward turbulent flow of air in a pipe

Conclusion We have demonstrated the possibility of using laser Doppler anemometers to investigate the characteristics of turbulent heterogeneous flows which carry solid doubly dispersed particles. The distribution has been obtained for the first time of the averaged and pulsation velocities of doubly dispersed particles moving in a turbulent flow of air in a pipe.     

Influence of particle density and size on turbulence, friction, and heat exchange characteristics

Numerical simulation of turbulent flows of a gas suspension in the vicinity of the critical point and in a channel with permeable walls has been carried out. The influence of the concentration of the dispersed phase and the size of its particles on the distribution of mean and pulsation characteristics of the flow, as well as on the friction and heat transfer coefficients, is discussed.     

Distribution of velocity pulsations in a channel with mixing of oppositely swirled streams

The influence of swirling and of the degree of concurrent flow on the magnitude and distribution of turbulent pulsations in the mixing of oppositely swirled streams is investigated. The correspondence between the pulsation characteristics of the mixing layers of swirled flows and concurrent jets is established.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 47–53, July, 1984.     

Convective coherent structures in a Hele-Shaw cell

Convective processes related to the onset of chaotic flows in a Hele-Shaw cell have been theoretically and experimentally studied. The properties of various modifications of a specific pulsation regime, in which certain characteristics exhibit chaotization with increasing Rayleigh number while the flow pattern remains statistically reproducible and retains a regular character, have been determined for the cavities with various ratios of the dimensions of wide sides. An analogy is established that allows pulsating vortices in the flow to be treated as simple coherent structures of a convective nature.     

Application of radio frequency method to measurements in cryogenics

This paper reports the specific features of the radio frequency method used to measure characteristics of cryogenic flows. The techniques for determination of the void fraction and quality of two-phase flows and the mean integral thermodynamic characteristics of single-phase flows, e.g. temperature and density, are described. The design and basic parameters of sensors with channels of round and annular cross-section are discussed. Possible combinations of these sensors with other devices for the measurement of two-phase and single-phase medium flow rates are shown. Information about the measuring system as well as measurement results for helium and nitrogen are presented. The sensor characteristics for hydrogen and methane have been estimated theoretically.     

输流管道参数共振实验研究

运用非接触测振技术对两端固定输流管道在脉动流作用下的参数共振问题进行了实验研究。通过搭建的实验平台,在功能上实现对流速、脉动频率以及脉动幅值的有效控制,实验通过激光测振技术获取实验管道的振动信息,通过多组测试,利用实验结果拟合出管道第一振型1/2次谐波参数共振区域,与理论计算结果定性上一致。     

Effect of flow pulsation on fluidization degree of gas-solid fluidized beds by using coupled CFD-DEM

In this paper, the effect of inlet flow type on fluidization of a gas-solid fluidized bed was studied by using numerical simulations. Gas-solid fluidized beds are widely used in processes such as heating, cooling, drying, granulation, mixing, segregating and coating. To simulate the gas-particle flows, the unresolved surface CFD‐DEM was used considering Eulerian–Lagrangian approach. The fluid phase was modeled by computational fluid dynamics (CFD) while the solid phase was solved by discrete element method (DEM), and the coupling between gas and solid phases was considered to be four-way. The uniform and pulsed flows were injected through three nozzles located at the bottom of a rectangular bed. Three types of pulsed flow were considered: sinusoidal, rectangular and relocating. The fluidized bed behavior was discussed in terms of minimum fluidization velocity (MFV), pressure drop, bubble formation, bed expansion, particles velocity and, gas-solid interaction and particle contact forces. The results of different simulations indicated that the minimum fluidization velocity of the beds fluidized by pulsed flows was decreased by up to 33%. The influence of the pulsation amplitude on the minimum fluidization velocity was more significant than that of the pulsation frequency. The bed expansion and particles average velocity were increased by the pulsed flows, while the pressure drop and interaction force were decreased. As the pulsation frequency increased, the pressure drop and gas-solid interaction force increased, although size of the bubbles and bed expansion decreased. It was also observed that in large vibration frequencies, the bubbles became more regular. In the sinusoidal flow, the velocity and contact force between the particles were initially increased by frequency and in larger frequencies they were decreased.     

一种基于冯卡门尺度的湍流模式在模拟稳态和非稳态流动问题中的应用

采用尺度自适应模型(SAS)对稳态和非稳态流动进行了数值仿真。SAS模型有效解决了传统脱体涡数值模拟(DES)方法在网格加密过程中引发的“附面层速度型偏离对数率”的问题;同时,SAS模型的尺度自解效应也赋予了该方法类LES特征,可以在不出现非物理解的前提下有效地释放当地脉动。通过高雷诺数平板边界层模拟,SAS方法在附面层内模拟的速度型分布与理论值贴合得很好,说明该方法对于稳态流动的求解并未偏离RANS模型;同时,在串联双圆柱算例中,SAS方法对于圆柱表面压力分布的预测精度高于其他稳态和非稳态模型,Q云图也显示出该方法的类LES特征。算例结果证明了SAS方法有着一定的工程使用价值。     

Interference of separated flows behind backward-facing step in the presence of passive control

The interaction of turbulent separated flows behind a backward-facing step in the presence of a passive miniturbulizer has been experimentally studied using digital particle-tracking velocimetry techniques. It is established that an obstacle placed in front of the step modifies the profiles of velocity and turbulent pulsation and significantly changes the length of a recirculation zone.     

大型活塞式压缩机性能试验装置中缓冲器的应用研究

一般采用气体流量计前加装缓冲器消除压缩机性能试验装置中气流脉动对测量精度的影响。本文分析2种适用于大型活塞式压缩机性能试验装置的缓冲器容积的计算方法,认为针对压缩机性能试验装置中的微小脉动气流,德国BORSIG的计算方法更加适合。搭建大型活塞式压缩机性能试验装置,利用经理论计算设计的缓冲器进行试验,发现即使在最大测试流量的情况下,缓冲器仍然可以很好地削减气流脉动的影响,从而大大提高压缩机试验装置的试验精度。     

Two-phase cryogenic flow meters: Part I – Realization of the calorimetric method

While operating with multicomponent flows, one needs to determine such characteristics as temperature, pressure, mass flow rate and component composition – mass quality, and void fraction. The main attention is given to measurement of mass flow rate of the two-phase cryogenic flows which can be used for superconducting accelerators, refueling hydrogen system for space and liquid natural gas industry, in particular. On the one hand, a two-phase flow is one of the simplest cases of multi-component flows which can be observed in cryogenics. On the other hand, this is rather sophisticated problem in cryogenics to create two-phase flow meters and estimate their metrological characteristics. This problem is discussed. Two methods are suggested – calorimetric and pressure drop ones. Features of the calorimetric method are discussed in this part.     

转子径长比对凸轮泵性能影响的数值模拟与试验

为了揭示径长比对凸轮泵性能参数的影响规律,建立不同径长比与凸轮泵特性曲线之间的定量关系,并获得轴系径向载荷分布特性,从而为凸轮泵轴系强度计算提供依据。基于FLUENT动网格技术和RNG k-ε湍流模型对凸轮泵进行三维瞬态流场数值计算,比较了6种不同径长比凸轮泵的流量特性。结果表明:径长比对凸轮泵性能有显著的影响,随着转子径长比的逐渐增大,凸轮泵出口流量脉动呈逐渐下降的趋势,且出口流量值先增大后减小;转子所受径向力的大小和方向均随转子转动呈周期性变化,且大小随径长比的增大而减小,随泵出口压力的增大而增大。数值计算表明当转子径长比α取值为0.7~1.3时,泵出口平均流量达到峰值区,同时泵出口流量脉动幅值最低,转子受力较好。研究结论为凸轮泵转子径长比的选择提供了理论依据。     

Digital self-calibration method for MEMS sensors

This paper presents a digital self-calibration method for microelectromechanical systems (MEMS) using a relay-feedback loop and a set of discrete-time filters. This method is based on the measurement of limit-cycles at the comparator's output, which result from a synchronization phenomenon between the natural frequency of the MEMS and the clock frequency of the discrete-time components. We show how quantized information concerning the MEMS parameters may be extracted from the shape of the limit-cycle, which depends on the characteristics of the MEMS (pulsation, damping, etc.). This digital technique is amplitude-independent, relatively insensitive to noise, and not costly to implement. Details concerning its implementation are discussed, and some simulation and experimental results are given.     

永磁无刷直流电动机换相脉动转矩及抑制方法

通过分析永磁无刷直流电动机的换相过程,得到了电动机绕组电流换相产生的脉动转矩表达式。为了验证理论分析的正确性,首先对电流换相产生的脉动转矩及相关特性进行了仿真,然后采用永磁旋转角加速度传感器对电动机轴上的脉动转矩进行了实际测量,验证了电机输出转矩中的脉动转矩分量的客观存在性及相关特性。针对脉动转矩,提出了一种基于峰谷互补的抑制方法,并建立了对应的实验平台开展了实验研究,理论分析和实验测量取得了一致的结果,从而证明了该抑制方法的正确性。     

Correlations study in shock wave/turbulent boundary layer interaction

The shock waves/turbulent boundary layer interaction is a problem of critical importance that is frequently encountered in designing flying vehicles. Presently, the most topical issue is the investigation of nonstationary phenomena (in particular, low-frequency effects) involved in this interaction. We have experimentally studied separated flows in the zone of interaction between an obliquely incident shock wave and a turbulent boundary layer at a Mach number of M = 2. Correlation data in the separation zone and the upstream flow were obtained. It is established that low-frequency oscillations in the reflected shock are related to the pulsation in the inflow boundary layer.     

A Study of Measurement-Based Traffic Models for Network Diagnostics

In this paper, the measurement and analysis of network flows are taken into account as a methodology for characterization and diagnosis of network behavior. The accuracy of flow models will be discussed, reviewing the basic underlying assumptions. A modeling approach based on multidomain analysis will be proposed, where flow measurements can be complemented by a limited amount of protocol data gathered from packet headers. By the analysis of experimental data, we argue that, in several situations, traffic may be more appropriately modeled by the superposition of multiple flows with different characteristics, which results in better measurements and improved diagnostic possibilities.      

泵—马达液压传动系统中的压力拍振分析

在泵—马达液压传动系统中,由于泵和马达的周期性吸油排油,不可避免地存在流量脉动,当泵和马达脉动的频率相接近时,系统会发生压力拍振现象。建立泵-马达传动系统的压力脉动数学模型,从理论上分析压力拍振的周期和幅值特点。采用集中参数法建立泵-马达传动系统的仿真模型,并通过仿真和试验分析系统压力拍振的规律,结果表明当泵和马达脉动频率比较接近时会发生压力拍振且拍振幅值随频率接近程度增加而增加。在压力拍振机理分析的基础上,提出合理选取传动比和柱塞数目可以有效抑制系统压力拍振。