Three-dimensional channel flow of second grade fluid in rotating frame

An analysis is performed for the hydromagnetic second grade fluid flow between two horizontal plates in a rotating system in the presence of a magnetic field. The lower sheet is considered to be a stretching sheet, and the upper sheet is a porous solid plate. By suitable transformations, the equations of conservation of mass and momentum are reduced to a system of coupled non-linear ordinary differential equations. A series of solutions to this coupled non-linear system are obtained by a powerful analytic technique, i.e., the homotopy analysis method （HAM）. The results are presented with graphs. The effects of non-dimensional parameters R, A, M2, a, and K2 on the velocity field are discussed in detail.

Effect of mold and core preheating temperature on corrosion resistance of casting Al-12Si alloy U-shaped cooling channel

Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method.The effect of preheating temperature of the mold and the carbon fiber core on the roughness and corrosion resistance of U-shaped cooling channels made of Al-12Si alloy was examined in depth.The experimental results suggest that as the preheating temperature increased from 273 K to 573 K,the roughness of the inner wall of the cooling channel reduced from 96.6μm to 77.0μm.When the preheating temperature continued to increase to 723 K,the roughness increased to 85.3μm.The wetting between the Al melt and the carbon fiber will reduce micro bubbles and waves on the channel wall as the preheating temperature rises,thereby reducing the roughness.However,with the further increase of preheating temperature,it will increase the solidification time of the Al melt.At this time,the carbon fiber and Al melt will take more time to react,which increases the roughness of the channel wall to a certain extent.The results of exfoliation corrosion show that the larger roughness will aggravate exfoliation corrosion.The prolongation of high temperature reaction time between the carbon fiber and the Al melt will lead to the segregation of Si,which is easy to cause intergranular corrosion.Therefore,reasonable preheating temperature has an important impact on the roughness and corrosion resistance of U-shaped cooling channels.

Hall Current Effects on Unsteady MHD Flow in a Rotating Parallel Plate Channel Bound-ed by Porous Bed on the Lower Half—Darcy Lapwood Model

We discussed the unsteady flow of an incompressible viscous fluid in a rotating parallel plate channel bounded on one side by a porous bed under the influence of a uniform transverse magnetic field taking hall current into account. The perturbations are created by a constant pressure gradient along the plates in addition to the non-torsional oscillations of the upper plate. The flow in the clean fluid region is governed by Navier-Stoke’s equations while in the porous bed the equations are based on Darcy-Lapwood model. The exact solutions of velocity in the clean fluid and the porous medium consist of steady state and transient state. The time required for the transient state to decay is evaluated in detail and ultimate quasi-steady state solution has been derived analytically and also its behaviour is computationally discussed with reference to different flow parameters. The shear stresses on the boundaries and the mass flux are also obtained analytically and their behaviour is computationally discussed.

Robust Quantum Secure Direct Communication over Collective Rotating Channel

A quantum secure direct communication protocol over a collective rotating channel is proposed. The protocol encodes logical bits in noiseless subspaces, and so it can function over a quantum channel subjected to an arbitrary degree of collective rotating noise. Although entangled states are used, both the sender and receiver are only required to perform single-particle product measurement or Pauli operations. The protocol is feasible with present-day technique.

Discussion on Standardization and Automatic Flow Measurement of U-shaped Channel Water

In human life,water resources are inseparable.In recent years,China’s population growth has accelerated,and the industrial level has been continuously improved,resulting in the rapid use and waste of water resources.The protection and rational distribution of water resources are the most pressing issue in China’s water resources.At present,the water measuring facilities of the U-shaped channel mainly include a straight wall measuring pool,a parabolic throat measuring pool,and a long throat measuring pool.In view of the problems in irrigation measurement,the empirical water measurement of basic open-channel and automatic flow measurement system in irrigation district is summarized to improve the accuracy,fairness,and rationality of water measurement,and promote irrigation district management to a higher level.

Hall Effects on Unsteady MHD Three Dimensional Flow through a Porous Medium in a Rotating Parallel Plate Channel with Effect of Inclined Magnetic Field

In this paper, we make an initial value investigation of the unsteady flow of incompressible viscous fluid between two rigid non-conducting rotating parallel plates bounded by a porous medium under the influence of a uniform magnetic field of strength H0 inclined at an angle of inclination α with normal to the boundaries taking hall current into account. The perturbations are created by a constant pressure gradient along the plates in addition to the non-torsional oscillations of the upper plate while the lower plate is at rest. The flow in the porous medium is governed by the Brinkman’s equations. The exact solution of the velocity in the porous medium consists of steady state and transient state. The time required for the transient state to decay is evaluated in detail and the ultimate quasi-steady state solution has been derived analytically. Its behaviour is computationally discussed with reference to the various governing parameters. The shear stresses on the boundaries are also obtained analytically and their behaviour is computationally discussed.

Rotating electroosmotic flow of an Eyring fluid

A perturbation analysis is presented in this paper for the electroosmotic (EO) flow of an Eyring fluid through a wide rectangular microchannel that rotates about an axis perpendicular to its own. Mildly shear-thinning rheology is assumed such that at the leading order the problem reduces to that of Newtonian EO flow in a rotating channel, while the shear thinning effect shows up in a higher-order problem. Using the relaxation time as the small ordering parameter, analytical solutions are deduced for the leading- as well as first-order problems in terms of the dimensionless Debye and rotation parameters. The velocity profiles of the Ekman-electric double layer (EDL) layer, which is the boundary layer that arises when the Ekman layer and the EDL are comparably thin, are also deduced for an Eyring fluid. It is shown that the present perturbation model can yield results that are close to the exact solutions even when the ordering parameter is as large as order unity. By this order of the relaxation time parameter, the enhancing effect on the rotating EO flow due to shear-thinning Eyring rheology can be significant.

Research and development of advanced structured packing in a rotating packed bed

As the core component of the rotating packing bed,packing is a place for efficient gas–liquid mixing and mass transfer.In this paper,a 3D structured packing composed of a mesh structure and a support structure was designed.The mesh structure is a ring-shaped mesh surrounded by triangular meshes,which is stable in structure and can achieve a high degree of dispersion and aggregation of the liquid phase.The support structure is composed of ring-shaped structural units arranged at a certain angle along the axial direction,which can enhance the turbulence of the airflow while constructing regular gas-phase channels.Circumferential steel meshes of different diameters and supporting structures are alternately combined to form 3D packing,which is loaded in a layered cross-flow rotating packing bed.The results show that under the same operating conditions,the mass transfer performance of 3D packing and wire mesh packing are equivalent,and both are better than pall ring packing.Moreover,the pressure drop of 3D packing is significantly lower than that of pall ring packing and wire mesh packing.The design and implementation of packing the development presented in this paper can be used to develop special structured packing for rotating bed,which can further improve the performance of rotating packed bed(RPB).

REYNOLDS-STRESS MODELLING OF TURBULENT ROTATING FLOWS

The present analysis shows that the EVM can not reflect the turbulence physics in non-inertial frame. The effects of Coriolis force on turbulence is embodied naturally in the Reynolds-stress transport equation. It is observed that the existing second-moment closure model with appropriate near-wall treatment can adequately predict flows in rotating channel and in axially rotating pipe for moderate rotation rate.

Vertical rotation effect on turbulence characteristics in an open channel flow

This paper solves the three-dimensional Navier-Stokes equation by a fractional-step method with the Reynolds number Reτ=194 and the rotation number Nτ=0-0.12. When Nτ is less than 0.06, the turbulence statistics relevant to the spanwise velocity fluctuation are enhanced, but other statistics are suppressed. When Nτ is larger than 0.06, all the turbulence statistics decrease significantly. Reynolds stress budgets elucidate that turbulence kinetic energy in the vertical direction is transferred into the streamwise and spanwise directions. The flow structures exhibit that the bursting processes near the bottom wall are ejected toward the free surface. Evident change of near-surface streak structures of the velocity fluctuations are revealed.

De-emulsification of 2-ethyl-1-hexanol/water emulsion using oil-wet narrow channel combined with low-speed rotation

Low-speed rotation of disc in an internal circulation of a novel de-emulsification with rotation-dise horizental contactor(RHC-D) realized de-emulsification for O/W emulsions due to repeated coalescence in oil-wet narrow channels at a low rotation speed. For three emulsions included ethanol/water/2-ethyl-1-hexanol, ethanol/water/2-ethyl-1-hexanol/SDS(Sodium Dodecyl Sulfonate) and 2-ethyl-1-hexanol/water/SDS emulsion, deemulsification ratios of oil phase could reach 1, 1 and 0.67 respectively at 170 r·min-1, and de-emulsification ratios increased obviously after agitating 10 min. De-emulsification experiment in the seam indicated that oil droplet sizes in O/W emulsion became larger after de-emulsification. The main de-emulsification mechanism in RHCD was the coalescence of oil droplets in oil-wet narrow channels. With increase of the rotation speed, oil droplets dispersed better in the aqueous phase. However, de-emulsification effect enhanced due to the increase of the coalescence rate at a bit higher rotation speed. In addition, internal circulation made those O/W emulsions to be broken repeatedly, consequently de-emulsification ratio increased. Repeated de-emulsification through internal circulation might make continuous extraction of ethanol come true at a low rotation speed.

Network Based Real Time Condition Monitoring of Rotating Machinery

This paper presents the development of a network based real time condition monitoring system of rotating machinery. The system is built up in a double net structure consisting of local net (including client and server) and intranet. The client serves as a field data collector and processor that samples the vibration signals and process parameters of a machine monitored in the net and processes the sampled data. The data collected by the client are transmitted to the server that processes the data further and provides the results of the diagnosis of each machine to any distant terminals through intranet or internet. Such a structure of the monitoring system is advantageous in safety, reliability and reasonably shares the existing net resources. In order to ensure real time transmission of the data, two procedures of data transmission, virtual channel and data pool, are developed and applied in the monitoring system. The experimental results show that the monitoring system works well and is suitable to monitor a large group of rotating machines.

Application of novel super-exponential iteration algorithm in underwater acoustic channel

A novel variable step-size modified super-exponential iteration(MSEI)decision feedback blind equalization(DFE)algorithm with second-order digital phase-locked loop is put forward to improve the convergence performance of super-exponential iteration DFE algorithm.Based on the MSEI-DFE algorithm,it is first proposed to develop an error function as an improvement to the error function of MSEI,which effectively achieves faster convergence speed of the algorithm.Subsequently,a hyperbolic tangent function variable step-size algorithm is developed considering the high variation rate of the hyperbolic tangent function around zero,so as to further improve the convergence speed of the algorithm.In the end,a second-order digital phase-locked loop is introduced into the decision feedback equalizer to track and compensate for the phase rotation of equalizer input signals.For the multipath underwater acoustic channel with mixed phase and phase rotation,quadrature phase shift keying(QPSK)and 16 quadrature amplitude modulation(16QAM)modulated signals are used in the computer simulation of the algorithm in terms of convergence and carrier recovery performance.The results show that the proposed algorithm can considerably improve convergence speed and steady-state error,make effective compensation for phase rotation,and efficiently facilitate carrier recovery.

High-speed railway channel measurements and characterizations: a review

Wireless communication for high-speed railways （HSRs） that provides reliable and high data rate communi- cation between the train and trackside networks is a challenging task. It is estimated that the wireless communication traffic could be as high as 65 Mbps per high-speed train. The development of such HSR communications systems and standards requires, in turn, accurate models for the HSR propagation channel. This article provides an overview of ex- isting HSR channel measurement campaigns in recent years. Particularly, some important measurement and modeling results in various HSR scenarios, such as viaduct and U-shaped groove （USG）, are briefly described and analyzed. In addition, we review a novel channel sounding method, which can highly improve the measurement efficiency in HSR environment.

Effect of Brownian Diffusion on Squeezing Elastico-Viscous Nanofluid Flow with Cattaneo-Christov Heat Flux Model in a Channel with Double Slip Effect

The present study deals with the analysis of heat transfer of the unsteady Maxwell nanofluid flow in a squeezed rotating channel of a porous extensile surface subject to the velocity and thermal slip effects incorporating the theory of heat flow intensity of Cattaneo-Christov model for the expression of the energy distribution in preference to the classical Fourier’s law. A set of transformations is occupied to renovate the current model in a system of nonlinear ordinary differential equations that are numerically decoded with the help of MATLAB integrated function bvp4c. The effects of various flow control parameters are investigated for the momentum, temperature and diffusion profiles, as well as for the wall shearing stress and the heat and mass transfer. The results are finally described from the material point of view. A comparison of heat flux models of Cattaneo-Christov and Fourier is also performed. An important result from the present work is that the squeezing parameter is strong enough in the middle of the channel to retard the fluid flow.

Turbulent characteristics and rotation correction of wall function in rotating channel with high local rotation parameter

The turbulent fluctuation and the rotation correction of wall function law are investigated in the entrance section of a rotating channel. The one-dimensional hot wire probe and the X-type probe are utilized to measure the boundary layer at four streamwise stations. Through the analysis on the boundary layer near the leading side and trailing side, it is found that the turbulent fluctuation is promoted in the trailing side whereas suppressed in the leading side. This difference is attributed to the Coriolis instability near the trailing side. In addition, considering the local rotation parameter Rc, whose maximum absolute value is 0.014, is larger than that in previous research, whose maximum value is 0.007, the whole process of the relaminarization is captured. To understand this phenomenon better, the effects of the generation term and the Coriolis term in the transport equation of the Reynolds stress are discussed. In addition, the rotation correction of the viscous-Coriolis region and the Coriolis region are discussed, a new revising method for the wall function is proposed.

荷电颗粒在旋转环形通道内分离性能研究

为研究带电旋转环形通道内荷电颗粒的运动和沉积特性,本文使用计算流体力学两相流离散颗粒法对带电旋转环形通道内的荷电颗粒的运动过程进行了模拟。根据模拟结果分析了不同粒径、电压、入口雷诺数和通道长径比等参数对荷电颗粒运动和沉积的影响,研究了荷电颗粒在旋转通道内离心力与电场力之间的竞争关系,探索了离心力和电场力导致的荷电颗粒运动和沉积变化的规律。结果表明,单个不同粒径颗粒具有不同的颗粒逃逸电压区间,区间的大小随着颗粒粒径的增大而增大,且区间的宽度随着通道长径比的增大将会明显变小;多个颗粒的逃逸率曲线,不同粒径的颗粒将会有不同程度的交叉,随着长径比的增大,颗粒逃逸率曲线的高度与交叉会有明显的减小,而随着转速的增大,颗粒逃逸率曲线的交叉会有一定程度的减小,且高度不会有明显变化。

DIRECT NUMERICAL SIMULATION OF TURBULENT HEAT TRANSFER IN A WALL-NORMAL ROTATING CHANNEL FLOW

Direct Nmerical Simulation （DNS） of turbulent heat transfer in a wall-normal rotating channel flow has been carried out for the rotation number Nr from 0 to 0.1, the Reynolds number 194 based on the friction velocity of non ro taring case and the half-height of the channel, and the Prandtl number 1. The objective of this study is to reveal the effects of rotation on the characteristics of turbulent flow and heat transfer. Based on the present calculated results, two typical rotation regimes are identified. When 0 〈 Nr 〈 0.06, turbu lence and thermal statistics correlated with the spanwise veloc ity fluctuation are enhanced since the shear rate of spanwise mean flow induced by Coriolis force increases; however, the other statistics are suppressed. When Nr 〉 0.06, turbulence and thermal statistics are suppressed significantly because the Coriolis force effect plays as a dominated role in the rotating flow. Remarkable change of the direction of near wall streak structures based on the velocity and temperature fluctuations is identified.

发动机旋转部件温度实时无线测试系统设计

为了在航空发动机试验时,对旋转部件的温度状态进行实时监测,利用铂(Pt)薄膜热电阻温度传感器和STM32,设计了多通道温度实时无线测试系统。该系统以STM32控制多路选择开关和放大器等元器件,并使用其片内模/数转换器(ADC)对多路电信号进行转换,通过无线技术将温度数据发送到上位机。在涡桨发动机试验台完成了对桨叶的温度实时无线测量,解决了旋转部件无法引出信号线进行实时温度监测问题。实验结果表明,该系统的测量精度优于0.1℃,分辨率达到0.01℃。

基于轮采时间矩阵修正的单通道阵列系统设计与应用

针对常规多通道阵列工程实现所面临的多通道间幅相校准、同步采样等实际需求,以及由此产生的设备体积、重量、功耗、成本等急剧增大的难题,提出一种基于轮采时间矩阵修正的单通道阵列系统设计与应用方法。首先,射频轮采切换开关对各个阵元接收信号进行轮流采样,并通过单通道射频接收机完成射频到中频的信号转换。然后,单通道数字接收机接收单路中频信号进行数字信号处理,其关键步骤采用所提方法构建轮采时间矩阵对单通道阵列数据进行修正,确保修正后各阵元间数据相位关系满足阵列信号处理条件。最后,将单通道阵列数据应用于单通道阵列数字波束形成(Digital Beam Forming,DBF)和单通道超分辨测向等无源探测领域,使所提单通道阵列系统设计方法的工程应用成为可能,计算机仿真验证了该方法的有效性。