Unsteady air flow measurement method based on adaptive tracking differentiator for pneumatic system

When using a flowmeter to measure unsteady air flow in the pneumatic control system, problems such as high cost and pressure loss are often encountered. It is an available method to measure the unsteady flow rate using isothermal chamber through direct differentiation of pressure signal with a traditional fixed parameter differentiator, but the adaptability of this method is insufficient due to its narrow dynamic range. To this end, an improved adaptive tracking differentiator which can adaptively adjust the control parameters according to the changes of pressure signal and pressure tracking error was proposed for unsteady air flow measurement. The algorithm structure of the adaptive tracking differentiator was designed. Moreover, theoretical simulation and flow measurement experiments under multiple working conditions were carried out. The simulation and experiment results showed that the flow measurement method based on improved adaptive tracking differentiator effectively measured the unsteady flow in a wide dynamic range, and had the advantages of more simplified process and lower cost than traditional method.     

Unsteady flowmeter

An original method is presented to measure time resolved unsteady flow rate. From the kinetic energy theorem, the balance equation of the kinetic energy is integrated on a conical control volume (Venturi type). A non-linear ODE is obtained, simple enough to be resolved in real-time (that is to say in less than one time step). The two coefficients of the ODE depend only on the geometry of the device and are hence known by construction, it is therefore not necessary to calibrate the device. Experimental measurements at the intake of a combustion engine show that the device provides unsteady flow rate. By temporal integration, the unsteady measurements give a mean flow rate close to the reference flowmeter.The same analysis is then applied to a cylindrical control volume with a singular pressure drop (induce by a grid for example). In this case, one of the two coefficients of the ODE must be determined experimentally. Experimental measurements carried out with this device at the intake of a combustion engine show that this second method follows the flow fluctuations. A good agreement is found between unsteady measurements integrated over a whole number of periods and reference mass flowmeter. The inversions of direction of the flow are taken into account by the prototype. This device, more compact than the conical version (Venturi type), allows real-time measurements of the unsteady flow rate.     

An isothermal temperature source with a large surface area using the metal-etched microwick-inserted vapor chamber heat spreader

For use of the thermal cycle of the biochemical fluid sample, the isothermal temperature source with a large surface area was designed, fabricated and its thermal characterization was experimentally evaluated. The comprehensive overview of the technology trend on the temperature control devices was detailed. The large surface area isothermal temperature source was realized by using the vapor chamber heat spreader. The cost-effectiveness and simple manufacturing process were achieved by using the metal-etched wick structure. The temperature distribution was quantitatively investigated by using IR temperature imaging system at equivalent temperatures to the PCR thermal cycle. The standard deviation was measured to be within 0.7°C for each temperature cycle. This concludes that the presented isothermal temperature source enables no temperature gradient inside bio-sample fluid. Furthormore it can be applied to the cooling of the electronic devices due to its slimness and low thermal spreading resistance.     

混流式水轮机的非定常流动分析

通过混流式水轮机定常和非定常流动计算,研究混流式水轮机在不同开度下的流动特点,阐述非定常流动分析结果。非定常流动计算结果表明:开度a12时,转轮出口靠近上冠处压力脉动不显著,中间流线和下环处脉动较为强烈;尾水管中涡带主要集中于直锥段,呈螺旋型,在肘管处逐渐变小消失。尾水管内部压力脉动主要集中在直锥段和肘管,频率为低频,是转频的0.233倍;其中直锥段脉动幅值较大,内外两侧压力脉动频率基本一致。开度a24时,转轮出口靠近上冠处没有回流,脉动小,中间流线和下环处压力脉动更为剧烈,脉动频率为转轮频率与叶片数乘积的倍数;尾水管涡带在直锥段水流形成的呈柱状涡,在肘管变成较小的螺旋型涡带,其结果是长的涡带在尾部形成像钻机式的切削作用,对水轮机效率和稳定性产生严重的影响,涡带的长度为研究混流式水轮机尾水管深度和优化设计提供理论依据。     

绕水翼空化非定常的动力特性

采用试验的方法研究绕水翼空化流动的非定常流体动力特性。试验在一闭式空化水洞针对一Clark-y型水翼进行。采用高速摄像技术观测不同空化阶段的空穴形态;应用自开发软件分析空穴形态随时间的变化;测量翼型所受的升阻力和升力方向的加速度;对上述的数据进行频谱分析。试验结果表明,绕水翼空化流动中,空穴形态及其对应的动力特性随时间的变化过程存在两种不同的模式。当4σ/2α6时,空穴平均相对长度为l/c0.7,由空穴形态和升力系数得到的功率谱峰值对应的斯特劳哈尔数大于0.3;当σ/2α4,空穴平均相对长度为0.7l/c1.0,绕水翼空化流动呈现明显的非定常性,翼型吸力面出现了大量空泡团周期性的脱落,升力系数功率谱峰值对应的斯特劳哈尔数在0.18左右,空泡团脱落频率不随空化数的变化而改变。     

A humidity generator with a test chamber system

For the calibration of relative humidity hygrometers and dew-point hygrometers with an open sensor, a test chamber system was constructed and connected to a dew-point generator. The system includes several small chambers connected in series. By reversing the flow direction, humidity and temperature gradients in the test chamber system are monitored during calibration measurements. This paper reports the construction of the test chamber system and the improvements in the construction and the analysis of the dew-point generator. A full uncertainty analysis is presented. The expanded uncertainty of the dew-point temperature and the relative humidity with the coverage factor k=2 are from ±0.05°C to ±0.08°C and from ±0.1%rh to ±1.0%rh, respectively. Although the dew-point temperature range is from −40°C to +77°C, the limits for the temperature range of the test chamber system are −20°C and +60°C. The system was not tested with relative humidity values lower than 10% or higher than 95%.     

Optimization of transition curve of casing cavity of profiled chamber flow sensor

Profiled chamber flow sensor is a newly-designed rotary displacement flow sensor. Its stator has an inner chamber with two circular arc surfaces and two noncircular arc surfaces. The shape curve of the noncircular arc surfaces is defined as transition curve, which directly affects the performance characteristics of the sensor. This paper deals with an optimization method for determining the transition curves. At first, design considerations on the transition curves including their geometric features and requirements of kinematics and dynamics are discussed, and a set of derivation constraints are formulated. Next, based on the constraints, the goal functions in polynomial forms with 3, 5, 7, 9°, are deduced. Finally, by comparing velocity, acceleration and jerk of the derived functions, optimal results for the transition curves are provided.     

Unsteady viscous flows past blunt bodies at moderate Reynolds numbers

Unsteady viscous flows past blunt bodies are simulated at the Reynolds numbers of 100, 200, 300, and 400. This research focuses on understanding the effects of the Reynolds numbers and blunt body shapes on the unsteady lift and drag forces. The incompressible Navier-Stokes flow solver, which employs the SIMPLER method in the two-dimensional body-intrinsic orthogonal curvilinear coordinate system, is verified by comparing the present numerical results with currently available experimental and numerical data. In conclusion, it is observed that the body shapes and the Reynolds numbers affect significantly the frequencies of the force oscillations as well as the mean values and the amplitudes of the drag and lift force oscillations. This paper was recommended for publication in revised form by Associate Editor Kyung-Soo Yang Moon-Sang Kim received his B.S. degree from Seoul National University Bachelor, M.S. in KAIST, and Ph.D. in Uni-versity of Illinois at Urbana-Champaign. He served at an engineer at Korea Power En-gineering Inc., and a Senior En-gineer at the Agency for Defense Development. He is currently a professor of Korea Aerospace University.     

Data-based estimation and simulation of compressible pulsating flow with reverse-flow through an orifice

Highly compressible pulsating flows are often encountered in devices where knowledge of the flow rate is required but elimination of pulsations is not an option. The current work is a continuation of a previous investigation that characterized the orifice discharge coefficient C_d as a function of dimensionless groups based on pulsation characteristics. The experimental apparatus has been rebuilt in the current work to mitigate temperature and vibration problems, allowing pressure and ΔP measurements to be made very close to the test section with 159-mm of nylon tubing. Data was acquired for 77 operating conditions spanning a range of pulsation frequencies, mass flow rates and system pressures. They confirm previously reported low C_d's in 0.20 range (calculated from time-averaged pressures) at some high-pressure low-flow operating conditions. Computational Fluid Dynamics (CFD) simulations of 12 of these data points suggest that the low C_d's result from reverse flow. Flow direction changed several times during each pulsation cycle closely tracking the orifice ΔP. A ‘core-and-sheath’ phenomena was observed for reverse-flow operating conditions: a positive core flow surrounded by a sheath of negative flow transitioned to a negative core and positive sheath several times during each pulsation cycle. The simulations also suggested that velocity profiles at the orifice stay stable and similar to steady-state profiles except for periods of rapid transitions. Based on these results a data-based quasi-steady method of estimating pulsating flow has been proposed. A pair of forward and reverse flow C_d's chosen by the data are used to predict instantaneous forward and reverse flows using the steady-state orifice discharge equation for compressible flow. The instantaneous values are then summed up over the pulsation cycle to estimate average mass flow rate. Average prediction errors were within 6%. A previously proposed method where regression was used to model C_d as a function of dimensionless groupings was shown to produce similar results. Both methods are designed to extract information from experimental data in order to overcome theoretical limitations and experimental error. The data is available upon request for further understanding of the flow physics.     

基于Ansys workbench的双馈发电机滑环室通风系统分析

针对双馈发电机在风电机组运行过程中多次出现的滑环故障问题,将计算流体力学(CFD)技术应用到双馈发电机滑环系统分析中。开展了双馈发电机滑环室风路分析,建立了滑环室进出风口与通风情况的关系,提出了使用ANSYS workbench进行滑环室风路流体分析的方法;在获得最佳风路的基础上,使用ANSYS CFX软件对其滑环散热效果进行了评价,并将出口风速、温度仿真分析结果与实际情况进行了对比。研究结果表明,出口风速仿真值与测试值间最大偏差别为4.1%,温度仿真值与测试值间最大偏差别为4.67%,离心风扇式滑环系统较轴流风扇式滑环系统相比在滑环室碳粉清除与滑环散热效果更好。     

A rapid-flow perfusion chamber for high-resolution microscopy

Perfusion chambers employing laminar flow have dead volumes and unstirred layers which limit the minimum time required to effect a change in the local chemical environment of the sample. We have fabricated and tested a chamber capable of developing turbulent flow at reasonable flow rates of aqueous solutions. Transition to turbulence occurred at ≈1 mL s⁻¹. To minimize dead space, a dual-exit cross-flow pattern was employed. The chamber was designed to mount on optical microscope stages for visual sample observation supplemented by a variety of techniques, such as fluorescence, light scattering and electrochemical monitoring. As indicated by fluorescence from a fluorescein-labelled protein film adherent to the chamber wall, local pH changes were produced within 200 ms. Use of the chamber is illustrated by measurements of stopped-flow kinetics in both calcium-triggered cortical granule exocytosis and influenza virus haemagglutinin-mediated cell–cell fusion.     

定常及非定常射流泵性能及管道摩阻试验研究

探讨非恒定条件下射流泵性能及与频率有关的管道摩阻损失,并与恒定流进行对比试验。试验结果表明,在相同的条件下,非恒定流射流效率比恒定流效率高。在频率f=1～2Hz范围内,频率越高,管道摩阻损失越大。     

Calibration of weirs using unsteady flow

This paper presents a method for unsteady calibration of rectangular and triangular weirs using height measurement instead of another flow measurement device as a standard. The theoretical equation of the dependence of the flow with the head for that weir, as long as the covered area, must be known. The method is theoretically developed and applied to a rectangular and to a triangular type of weir obtaining very good results when compared to other studies. In both cases the coefficients of discharge values were 0.617 and 0.587, respectively, which is very well within the values obtained by other researchers. In those analysis, the coefficient of determination of was as high as 0.998.     

双流道泵内非定常流动数值模拟及粒子图像测速测量

为探讨双流道泵内部的非定常流动机理,采用Fluent软件,基于滑移网格技术、 湍流模型计算了一双流道泵在不同工况下的内部流动,并将计算结果与粒子图像测速仪(Particle image velocimeter, PIV)实测结果进行比较。结果表明：计算所得双流道泵内部流场符合叶轮机械内部流动的一般规律,且与PIV实测结果总体变化趋势一致;由于双流道泵结构特殊,其进口处的流动状态与普通叶轮相差较大,出口处的流动状态与普通叶轮类似;叶轮进口处,流体基本沿流道吸力面流动,流道工作面上的相对速度很小,存在严重的脱流和旋涡;叶轮出口处,压力面和吸力面的速度趋于相等,射流—尾迹现象并不明显;由于叶轮—蜗壳动静干涉,两个叶轮流道内的静压分布有所不同;同一流道内,静压随着半径的增加而逐步增大,压力面侧静压大于吸力面侧;蜗壳流道内静压随半径增大,最大静压值在隔舌处。此项研究不仅加深了人们对双流道泵内非定常流动图画的理解,从而进一步完善双流道泵设计方法,同时也可为其他类型泵的内流研究提供借鉴。     

Unsteady viscous flow over elliptic cylinders at various thickness with different reynolds numbers

Two-dimensional incompressible Navier-Stokes equations are solved using SIMPLER method in the intrinsic curvilinear coordinates system to study the unsteady viscous flow physics over two-dimensional ellipses Unsteady viscous flows over various thickness-to-chord ratios of 06, 08, 10, and 1 2 elliptic cylinders are simulated at different Reynolds numbers of 200, 400, and 1,000 This study is focused on the understanding the effects of Reynolds number and elliptic cylinder thickness on the drag and lift forces The present numerical solutions are compared with available experimental and numerical results and show a good agicement Through this study, it is observed that the Reynolds number and the cylinder thickness affect significantly the frequencies of the force oscillations as well as the mean values and the amplitudes of the drag and lift forces     

Numerical simulation of turbulent flow in the suction chamber of a gearpump using deforming mesh and mesh replacement

The flow in the suction chamber of an external gearpump is numerically analysed. The evolution of the boundaries of the domain is very complex, and an arbitrary Lagrangian-Eulerian (ALE) formulation is used with mesh deformation and local remeshing. Nevertheless, a mesh replacement strategy is also adopted in order to avoid skewed meshes and allow for simulation of solid contact between gears. This process approximates a more realistic flow behaviour when the working pressure is larger than 10 bar, which is an important in fluid power systems where the pressure is usually greater than 100 bar.Aside from the laminar model, which fails as a result of the vortex configuration in the suction chamber, Standard k-ε, RNG k-ε, Realizable k-ε and Reynolds Stress Models (RSM) are tested. The numerical flow is compared with experimental data obtained with Time Resolved Particle Image Velocimetry. Although all of the models failed in some respect, the RSM and RNG k-ε were the best choice provided its behaviour close to the gearing zone and general shape of the vortex distribution.     

Measurement of horizontal flow in a large scale furnace using acoustic vector tomography

Acoustic pyrometry is one of only a few techniques that can give information about temperature and flue gas velocity in a large scale furnace of a coal fired power station. The time of flight of acoustic signals through the furnace is influenced by both temperature and gas velocity. Here, the reconstruction of the velocity of gas from acoustic measurements via vector tomography is considered. A reconstruction algorithm based on a stable series expansion method for vorticity and a finite difference method for the nonrotational part of the vector field is presented. It is applied to realistic synthetic data and data measured at a large scale furnace.     

轴流式水泵非定常湍流数值模拟的若干关键问题

为准确捕捉轴流式水泵不稳定流场特征,采用雷诺时均法和大涡模拟方法对轴流泵非定常湍流进行数值模拟,并就相关问题进行深入研究。研究发现,与其他湍流分析方法相比较,大涡模拟方法在轴流泵非定常流场分析中具有更高的计算精度;同时将轴流泵进水流道与泵段一起进行流场计算后,发现叶轮进口的流动是极不均匀的,靠近弯肘形流道内侧的速度明显大于其他部位,这一现象与通常假定的轴流泵进口流动是均匀的设计与分析理论有很大区别。研究还发现,为了获得轴流泵流场内不同压力脉动频率成份,脉动计算的采用样时间应不少于8个旋转周期;轴流泵内部的水压力脉动幅值在叶轮附近区域沿半径逐渐增大,而在导叶出口之后沿半径逐渐减小。     

Flow structure in critical flow Venturi nozzle and its effect on the flow rate

The flow fields in toroidal Venturi-nozzles, shaped according to the ISO-9300 Standard, have been investigated using numerical flow simulation. The present study was aimed at clarifying some of the phenomena associated with unchoking the flow in the throat. To this end, the shock structure has been studied for different Reynolds numbers and exit pressure ratios. The flow simulations were carried out in two and three dimensions. The flow fields were always unsteady, displaying a complex shock–boundary layer interaction.