基于磁流体的新颖惯性引力传感器

利用磁流体及其复合物独特的电磁属性和机械流变的磁流体惯性引力新颖传感器具有低成本、高线性、高灵敏度的特征．特别在准静态和低频惯性引力变化场合中。具有高的线性度和灵敏度响应。具体以磁流体低频加速度计、角速度测量和磁流体复合物重力梯度传感器为例来说明磁流体及其复合物惯性引力传感器的工作原理。并简单介绍了它们的试验结构模型和试验结果．这种新型传感器具有重要的理论研究和应用推广价值。     

新型磁流体复合物惯性引力传感器

利用磁流体复合物独特的电磁属性和机械流变的新颖磁流体惯性引力传感器具有低成本、高线性、高灵敏度的特征，特别在准静态和低频惯性引力变化场合中，具有高线性度和灵敏度响应。具体以磁流体复合物加速度计、角速度测量和磁流体复合物重力梯度传感器为例来说明磁流体复合物惯性引力传感器的工作原理，并简单介绍了它们的试验结构模型和试验结果。这种新型传感器具有重要的理论研究和应用推广价值。     

磁流体动力学角速度传感器的温度特性分析北大核心CSCD

磁流体动力学角速度传感器基于磁流体动力学效应工作,导电流体置于旋转的磁场环境,切割磁感线产生感应电势。环境温度变化,会影响导电流体的黏度、电导率及磁通密度进而改变导电流体的响应状态,从而影响传感器的输出。文中从理论上分析了温度对传感器关键部件的影响,并利用MAXWELL及FLUENT进行耦合仿真,通过温度实验加以验证。结果表明:低频时导电流体的正温度效应小于永磁回路的负温度效应;中高频时,影响MHD角速度传感器表头温度稳定性的主导因素为永磁回路的负温度效应,为减小传感器温度漂移并进行结构优化设计提供依据。     

采用PWM静电伺服技术的微型角速度传感器

本文介绍了采用ＰＷＭ静电伺服技术的微型角速度传感器的结构组成，分析了其工作机理，提出了其基本的检测原理。采用ＰＷＭ检测技术，使微弱、低频信号的高精度检测成为现实。     

多通道施肥机水力特性及其结构优化研究

针对水肥一体化施肥机精量施肥与应用的要求,开展了多通道施肥机水力特性、结构优化及试验研究。利用FloEFD流体仿真分析软件,对单个射流泵及并联多个射流泵组成的吸肥器进行了流体仿真,通过研究通道数与吸肥量及水力特性对比关系,结合实际应用需求,优选了具有合适吸肥量和较优水力性能的三通道吸肥器并联组合对结构;对三通道并联结构参数进行了优化设计,确定了主管道和3个射流泵之间的合适长度,实现了每通道吸肥量趋于相同,并且吸肥量高于优化前;最后制作样机进行了试验验证。研究结果表明:三通道实验吸肥量相对误差最大为2.57%,吸肥量实验数据与数值模拟数据的误差小于5%,在合理范围内;样机长时间运行具有很好的稳定性。     

基于分区测速原理的工业两相流体流量测量方法研究

通过对工业流体流速分布规律的分析,提出了基于分区测速原理的两相流体流量测量方法.该方法把整个流体的流通截面划分为若干个信息窗区域,根据超声波多普勒测速原理,采用一个换能器发射信号,多个换能器接收信号的方式测量各信息窗区域内流体的流速值,然后利用"加权积分法"得到流体的流量.侧重论述了工业流体的流速分布规律,分区流速测量原理,以及加权积分法流量计算方程.试验证明,该方法有效减小了因流体流速分布不均而产生的测量误差,提高了多普勒流量计的测量精度.     

基于转动支承梁式的光纤光栅低频加速度传感器

为了实现低频振动的高灵敏度测量,设计了一种基于转动支撑梁的新型光纤布拉格光栅加速度计。 通过分析其振动 模型和 MATLAB 数值计算,优化了传感器的结构参数,设计传感器理论灵敏度为 1 725 pm / g,固有频率为 68. 4 Hz。 同时通 过 COMSOL 模拟分析传感器的动态特性,其模拟结果与理论分析吻合。 频响特性和幅值特性实验结果表明光纤光栅加速度 计在加速度 0 ~ 2 g、工作频率 0. 5 ~ 20 Hz 的范围内,传感器加速度特性曲线呈现良好线性关系,灵敏度高达 1 495. 2 pm / g,重 复性良好。 该传感器结构简单紧凑,轴承结构有效减少悬臂梁振动过程中的弹性能耗,可显著提高其灵敏度,能够实现低频 振动信号的探测。     

Lamb波压差式微流量传感器

为提高微流体系统中的流量检测灵敏度,增大动态检测范围,实现温度补偿,提出了一种基于Lamb波的压差式微流量传感系统.该传感系统主要由两个Lamb波压力传感器和微通道组成,它利用Lamb波薄膜内应力的敏感特性,以频率计量的方式间接测量微通道两端的压力差;并采用双Lamb波压力传感器构成差动式测量结构进行温度补偿.对长20 mm,宽1 mm,高50 μm的微通道进行了流量测试实验,结果表明:在流量测试范围内,微通道两端的频率差与流量基本呈线性变化,其线性相关系数为0.999 9;在微流量传感器未进行优化的前提下,最小检测量为0.627 μL/s.     

带凹穴渐缩型微通道传热与流动性能分析

针对电子器件的散热问题，设计了6种渐缩型微通道，并通过合理布置圆形凹穴来削减截面几何尺寸突变导致的压力损失。旨在借助凹穴结构促进微通道冷却液混合提升换热性能，以及通过优化通道几何尺寸来改善微通道的流体流速分布，从而进一步提升微通道换热性能。在高热流密度条件下，对6种带凹穴渐缩微通道和普通矩形微通道的流动换热特性进行了对比数值分析，并以泵功和热阻为评价指标来评价通道综合传热性能。结果表明：通过设置渐缩微通道凹槽及通道截面的合理分布，改善了流速的分布，使温度分布更加均匀，并且增强了其散热能力。在实验组的最优结构下，渐缩微通道热阻比普通矩形微通道降低了18.4%，综合传热性能最高提升了15.2%。     

磁流体动力学陀螺磁场均匀性分析及优化设计

为了改善磁流体动力学陀螺的低频响应,提出了将磁流体动力泵技术应用于磁流体动力学陀螺研制的方法,并用ANSYS对其磁路结构进行三维仿真。仿真结果表明,磁感应强度不均匀度远大于10%,严重影响传感器的精度。通过有限元仿真方法分析不同永磁体对工作间隙磁场的不同影响,并在结构设计中去除对磁场不均匀度影响较大的永磁体,最后通过合理的磁路设计方法,在实现工作间隙所需磁场的同时降低磁场的不均匀度。仿真结果表明:磁感应强度不均匀度小于10%。     

气体对磁流体动力学传感器影响机理的探讨

由于气体和导电流体性质上的差异,导电流体中气体的存在将对磁流体动力学(MHD)传感器的输出特性产生影响。基于电磁感应理论和两相流理论,文章推导并建立了导电流体中含气体的MHD传感器VOF模型。通过ANSYS Fluent对含气体的MHD传感器输出特性进行仿真分析,同时搭建试验平台对不同气体含量MHD传感器进行试验验证。结果表明,导电流体中的气泡在低频时容易被拉伸撕裂成小气泡并随着角振动分散,同时使得流体环流场和电场产生偏移和畸变,角振动频率越低,此现象越明显;当导电流体中不含气体时角振动频率和幅值、重力加速度及偏心等外部因素对MHD传感器的输出特性无影响;当导电流体中含有气体时,MHD传感器的输出特性畸变等随气体含量、重力加速度和偏心的增大而增大,随角振动频率和幅值的增大而减小。文章研究成果能够为MHD传感器导电流体灌装工艺控制提供指导,有助于MHD传感器精度和稳定性的提升。     

基于熵产的侧流道泵流动损失特性研究

侧流道泵是一种介于容积式泵和离心泵之间的径向式叶片泵。泵内流体以螺旋轨迹方式在叶轮和侧流道中反复运动,整个运动是一种典型的全三维、高湍流强度、空间非对称的湍流流动,因此不可避免地产生较大的流动损失。利用热力学第二定律,基于熵产的流动损失分析方法对一种单级侧流道泵模型湍流流动损失进行研究,主要通过理论和数值计算求解湍流流动过程中增加的熵产,定性分析侧流道泵流动损失出现的位置及分布特点。结果表明,侧流道泵内部流动损失主要与湍流流动增加的熵产有关,而热量交换产生的熵产相对较小,在侧流道泵的损失研究中可以忽略;叶轮流道和侧流道内的湍动耗散率均远远大于直接耗散率;叶轮流道内的损失主要出现在叶轮内缘至0.4 r处,在侧流道内,流动损失主要出现在流道进口、流道中间靠近内缘部分以及出口附近。     

基于损失计算的水泵性能综合预测及分析

以降低叶轮进口冲击混合损失为目标,对进口边为径向和轴向两种情况下的叶轮进口条件进行了优化,得到了相应的进口直径计算公式。基于流体力学理论,充分利用水泵进出口速度分布等宏观物理参量描述流体在叶轮流道内的流动,借助速度三角形分析计算离心泵内的各种损失,很好地揭示了几何参数对水泵性能的影响趋势,对水泵进行了综合性能预测。基于损失计算的水泵性能综合预测及分析方法可预测设计工况和非设计工况下的水泵性能,它集性能分析与设计于一体,为水泵新产品设计和现有产品改进提供了切实有效的工程实用方法。     

Numerical simulation and analysis of flow characteristics in the front chamber of a centrifugal pump

We performed numerical simulations to study the flow characteristic in a centrifugal pump based on the RANS equations and the RNG k-ε turbulent model. The flow field, including the front and back pump chambers, the impeller wear-ring, the impeller passage, the volute casing, the inlet section and outlet section was calculated to obtain accurate numerical results of fluid flow in a centrifugal pump. The flow characteristic was studied from the internal flow structure in pump chambers, the radial velocity at impeller outlet as well as the pressure inside of the pump, the circumferential velocity and the radial velocity in front pump chamber. The variation of flow parameters in internal flow versus flow rate in the centrifugal pump was analyzed. The results show that the overall performance of the pump is in good agreement with the experimental data. The simulation results show that the distribution of flow field in the front pump chamber is axial asymmetry. The energy dissipation at the impeller outlet is larger than other areas. The distribution of the circumferential velocity and that of radial velocity are similar along the axial direction in the front pump chamber, but the distribution of flow is different along the circumferential and the radial directions. It was also found that the vorticity is large at the impeller inlet compared with other areas.     

Performance study based on inner flow field numerical simulation of magnetic drive pumps with different rotate speeds

Magnetic drive pump has gotten great achievement and has been widely used in some special fields.Currently,the researches on magnetic drive pump have focused on hydraulic design,bearing,axial force in China,and a new magnetic drive pump with low flow and high head have been developed overseas.However,low efficiency and large size are the common disadvantages for the magnetic drive pump.In order to study the performance of high-speed magnetic drive pump,FLUENT was used to simulate the inner flow field of magnetic drive pumps with different rotate speeds,and get velocity and pressure distributions of inner flow field.According to analysis the changes of velocity and pressure to ensure the stable operation of pump and avoid cavitation.Based on the analysis of velocity and pressure,this paper presents the pump efficiency of magnetic drive pumps with different rotated speeds by calculating the power loss in impeller and volute,hydraulic loss,volumetric loss,mechanical loss and discussing the different reasons of power loss between the magnetic drive pumps with different rotated speeds.In addition,the magnetic drive pumps were tested in a closed testing system.Pressure sensors were set in inlet and outlet of magnetic drive pumps to get the pressure and the head,while the pump efficiency could be got by calculating the power loss between the input power and the outlet power.The results of simulation and test were similar,which shows that the method of simulation is feasible.The proposed research provides the instruction to design high-speed magnetic drive pump.     

Multi-Field Analysis and Experimental Verification on Piezoelectric Valve-Less Pumps Actuated by Centrifugal Force

A piezoelectric centrifugal pump was developed previously to overcome the low frequency responses of piezoelectric pumps with check valves and liquid reflux of conventional valveless piezoelectric pumps. However, the electro-mechanical-fluidic analysis on this pump has not been done. Therefore, multi-field analysis and experimental verification on piezoelectrically actuated centrifugal valveless pumps are conducted for liquid transport applications. The valveless pump consists of two piezoelectric sheets and a metal tube with piezoelectric elements pushing the metal tube to swing at the first bending resonant frequency. The centrifugal force generated by the swinging motion will force the liquid out of the metal tube. The governing equations for the solid and fluid domains are established, and the coupling relations of the mechanical,electrical and fluid fields are described. The bending resonant frequency and bending mode in solid domain are discussed, and the liquid flow rate, velocity profile, and gauge pressure are investigated in fluid domain. The working frequency and flow rate concerning different components sizes are analyzed and verified through experiments to guide the pump design. A fabricated prototype with an outer diameter of 2.2 mm and a length of80 mm produced the largest flow rate of 13.8 m L/min at backpressure of 0.8 k Pa with driving voltage of 80 Vpp. Bysolving the electro-mechanical-fluidic coupling problem,the model developed can provide theoretical guidance on the optimization of centrifugal valveless pump characters.     

Numerical and experimental investigations on the hydrodynamic radial force of single-channel pumps

In order to clarify the generation mechanism and characteristics of hydrodynamic radial force in single-channel pumps, the transient flow in three single-channel pumps was analyzed by computational fluid dynamics (CFD). The three pumps had the identical impeller but with a spiral volute (model 1), a circular volute (model 2), and a torus (model 3). Experiments on pump performance were performed and high frequency pressure sensors were mounted in the spiral volute to measure pressure distribution in the volute of model 1. It indicates that the numerical results are approximately consistent with the experimental results. The radial force is mainly caused by the pressure acting on the blade. The impeller radial force in model 1 was the largest while the model 3 was the smallest, as it is not affected by rotor stator interaction, and rotor stator interaction plays a vital role in the shock load of pumps. The radial forces of different rotational speed were analyzed and indicated that Reynolds number has little influence on the radial force coefficient C_F. The dominant frequency of the radial force on the impeller is the rotational frequency of impeller for all rotational speeds. Moreover, the amplitude of the radial force fluctuations increased with increasing flow rate in model 2, but the change was not obvious with the increasing of flow rate in model 3, while at lower flow rate the largest amplitude of the radial force fluctuations was presented in models 1.     

Experimental study on the impulsion port of a trochoidal wheeled pump

All positive displacement pumps produce a pulsating flow. The present paper reports the experimental measurement of steady flow pulsations in the outlet of the internal wheeled pump. In the measured flow, the manufacturing tolerance are responsible of part of the spectra of the whole pulsation. Time-Resolved Particle Image Velocimetry technique has been used for this purpose. The flow pulsation measurement from a direct visualization of the velocity profile was carried out. The flow rate signal is derived from ad-hoc integration algorithm of the radial velocity profile, where the area discretization is a constant parameter that is relevant to minimize PIV errors by velocity gradients regions near the wall. Spectrographic analysis on the experimental data reveled low frequency components related with manufacturing tolerances. Measurements of this non-invasive procedure are compared with detailed CFD numerical results obtained from an improved gerotor model where manufacturing tolerances have been included. To be compared, cross-power spectral density analysis has been applied. The results reported in the paper show a method to provide a fast non-invasive flow pulsation measurement not only for pumps but also could be extended to compare aging effects of other kind of fluid power devices.     

双吸双流道泵流动特性研究

为探讨双吸双流道泵的内部流动规律,本文基于CFD性能预测方法,计算泵在不同时刻和不同工况下的速度-压力分布,探讨其蜗壳喉部的速度分布和蜗壳内部的压力脉动。研究结果表明:叶轮进口处的流动状态与普通叶轮相差较大,在流道的工作面上存在脱流和旋涡。叶轮流道旋转至隔舌左侧靠近蜗壳出口时,叶轮流道以及蜗壳喉部的速度-压力分布均匀。各监测点为低频振动。此项研究可为进一步优化此类泵提供一定的参考。     

乳化液泵站变频恒压控制系统的研究

针对目前采用的由多台小流量乳化液泵组成的泵站,提出变频的控制方式,并进行变频控制系统硬件和软件设计。通过压力传感器检测泵站出口压力,采用变频技术调整乳化液泵电机的转速,达到控制泵站出口压力相对恒定的目的。