纵轴流风筛式清选装置多因素试验研究

为了改善纵轴流水稻收获机清选装置的清选性能,在自行研制了纵轴流风筛式清选装置试验台的基础上进行正交旋转试验研究,分析了清选装置的曲柄转速、离心风机转速、离心风机倾角三个参数对功耗、含杂率、损失率的影响.利用各性能指标的回归方程,采用主目标函数法,用MATLAB进行优化求解,综合评定后得到优化参数为:曲柄转速为235r/min,离心风机转速为764r/min,风机倾角为28°,通过验证试验后,所得到的性能指标均满足要求.通过研究,可为清选装置的设计、制造和使用提供可借鉴的依据.     

叶轮结构对离心风机流动特性及性能影响的研究现状

通过回顾近年来国内外对叶轮性能的研究现状,结合叶轮结构形式及参数对离心风机不同方面的影响,得出离心风机叶轮内的损失主要是叶道内沿程摩擦损失,叶片上边界层分离,叶轮径向出口速度分布不均匀引起的尾迹流,轴向涡流,叶道进口冲击损失等。并指出今后的研究应以试验研究与采用CFD相结合的方法,在风机设计时考虑上述影响因素,从而降低叶轮内损失,提高离心风机性能。     

Performance of a cross-flow fan with various shapes of a rearguider and an exit duct

A cross-flow fan having forward curved blades relatively produces higher dynamic pressure at low rotating speed because a working fluid passes through an impeller blade twice. Most of this dynamic pressure is transferred to the static pressure in a rearguider and a stabilizer as a scroll in the centrifugal fan. The effect of a rearguider and a stabilizer on the performance of a cross-flow fan is higher than that of the impeller. Therefore, it should be considered how the shape of a rearguider and an exit duct affects on the performance and the flow fields. The purpose of this study is to investigate the reciprocal relation to the flow field and performance among the design parameters. Two-dimensional, unsteady governing equations are solved using FVM algorithm, sliding grid system and standard k - ɛ turbulence model. Verlocity profiles with various parameters are depicted. Furthermore, the meridional velocity profiles around the impeller are plotted at fixed rotating speed and design flow rate. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Behavior of rotating stall cell in a high specific-speed diagonal flow fan

An experimental investigation was carried out to clarify unsteady flow fields with rotating stall cell, especially behavior of stall cell, in a high specific-speed diagonal flow fan. As its specific-speed is very high for a diagonal flow fan, its pressure-flow rate curve tends to indicate unstable characteristics caused by rotating stall similar to axial flow fan. Although for an axial flow fan many researchers have investigated such the flow field, for a diagonal flow fan little study has been done. In this study, velocity fields at rotor inlet in a high specific-speed diagonal flow fan were measured by use of a single slant hot-wire probe. These data were processed by using the ““Double Phase-Locked Averaging“ (DPLA) technique, i. e. phases of both the rotor blade and the stall cell were taken into account. The behaviors of stall cell at rotor inlet were visualized for the meridional, tangential and radial velocity.     

Experimental study on the mean flow characteristics of forward-curved centrifugal fans

Measurements have been made in an automotive HVAC blower for two different centrifugal fans. This work is directed at improving the performance of a conventional forward-curved centrifugal fan for a given small blower casing. Mean velocities and pressure have been measured using a miniature five-hole probe and a pressure scanning unit connected to an online data acquisition system. First, we obtained the fan performance curves versus flow rates showing a significant attenuation of unstable nature achieved with the new fan rotor in the surging operation range. Second, aerodynamic characterizations were carried out by investigating the velocity and pressure fields in the casing flow passage for different fan operating conditions. The measurements showed that performance coefficients are strongly influenced by flow characteristics at the throat region. The main flow features were common in both fans, but improved performance is achieved with the new fan rotor, particularly in lower flow rate regions. Based on the measured results, design improvements were carried out in an acceptable operation range, which gave considerable insight into what features of flow behavior were most important.     

Numerical analysis for prediction of flow rate of the motor cooling fan

In this study, we analyzed the three dimensional unsteady flow around a motor cooling fan using the vortex panel method. For a popular type of motor cooling fan that has thin blades, we predicted the flow rate through numerical analysis without experimental data, such as the free stream velocity, which is a boundary condition of the flow field. We also calculated the flow rate for various cooling fan geometries and rotating speeds. For these fans, the numerical results showed flow rates within 3% of the experimental results. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

一种新型结构风机设计及其性能测试

为满足工业领域对高压比、低流量风机的需求,设计了一种新型结构的小尺寸、高压比、低流量风机。该风机在结构上不同于轴向进风、轴向出风的轴流风机,也不同于轴向进风、径向出风的离心风机,而是采用了径向进风、径向出风的结构。文章对该风机的结构特点、工作原理进行了详细介绍,并对风机的流量和压力进行了初步测试。测试结果表明:该新型结构风机在叶轮直径为110 mm,电机转速为6000 r/min的工况下,极限压力可高达7.4 kPa,极限流量可高达226.69 L/min。     

低速电驱离心压气机特定工况下内部流场的数值模拟

以压气机的三维流场作为主要研究对象,离心式径流风机为基础模型,确定车用增压器压气机蜗壳和叶轮大致尺寸参数,在此基础上,建立三维整体装配模型,对其进行了数值模拟,对各种离心压气机模型的性能进行预测,分析不同数量、形态叶片的叶轮对效率性能和内部流场压力速度分布的影响。通过计算结果的校核以确定离心压气机叶轮的合理配置方案,了解该离心压气机特定工况下的内部流动情况,以达到设计目标的要求,并为实现快速设计提供依据。     

Study of flow instability in a centrifugal fan based on energy gradient theory

Flow instability in a centrifugal fan was studied using energy gradient theory. Numerical simulation was performed for the threedimensional turbulent flow field in a centrifugal fan. The flow is governed by the three-dimensional incompressible Navier-Stokes equations coupled with the RNG k-ε turbulent model. The finite volume method was used to discretize the governing equations and the Semi-implicit method for pressure linked equation (SIMPLE) algorithm is employed to iterate the system of the equations. The interior flow field in the centrifugal fan and the distribution of the energy gradient function K are obtained at different flow rates. According to the energy gradient method, the area with larger value of K is the place where the flow loses stability easier. The results show that instability is easier to generate in the regions of impeller outlet and volute tongue. The air flow near the hub is more stable than that near the shroud. That is due to the influences of variations of the velocity and the inlet angle along the axial direction. With the decrease of the flow rate, instability zone in a blade channel moves to the impeller inlet from the outlet and the unstable regions in different channels develop in opposite direction to the rotation of impeller.     

A numerical study on the unsteady flow behavior and the performance of an automotive sirocco fan

An automotive sirocco fan has been widely used in air-conditioning devices. It is essential to understand the flow characteristics of an automotive sirocco fan to satisfy the trends for more efficient and less noise. In this study, numerical calculations were conducted to explain the three-dimensional unsteady, incompressible flow characteristics and performance of the sirocco fan using FLUENT. Reynolds-averaged Navier-Stokes equations with the standard k - ɛ turbulence model were used for the numerical analysis. The sliding mesh was used to simulate the relative transient motion of impeller against scroll. It was found that the inactive zone and the secondary flow reduce efficiency because they cause internal losses. A parametric study was performed to improve efficiency of the sirocco fan, using two geometric variables. Reducing the width of impeller could decrease the relative size of inactive zone and secondary flow. Changing the position of cut-off had little influence on the efficiency. Thus an improvement of efficiency could be achieved by reducing the width of impeller. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Numerical and experimental investigation of the bell-mouth inlet design of a centrifugal fan for higher internal flow rate

The energy efficiency of a household refrigerator is one of the most critical characteristics considered by manufacturers and consumers. Numerous studies in various fields have been conducted to increase energy efficiency. One of the most efficient methods to reduce the energy consumption of a refrigerator is by improving the performance of fans inside the refrigerator. A number of studies reported various ways to enhance fan performance. However, the majority of these studies focused solely on the fan and did not consider the working environment of the fan, such as the inlet and outlet flow characteristics. The expected performance of fans developed without consideration of these characteristics cannot be determined because complex inlet and outlet flow passage could adversely affect performance. This study investigates the effects of the design of the bell-mouth inlet on the performance of a centrifugal fan in a household refrigerator. In preliminary numerical studies, significant flow loss is identified through the bell-mouth inlet in the target fan system. Several design factors such as tip clearance, inner fence, motor-box struts, and guide vane are proposed to resolve these flow losses. The effects of these factors on fan performance are investigated using computational fluid dynamics techniques to solve incompressible Reynolds-averaged Navier-Stokes equations for predicting the circulating flow of the fan. Experiments are then performed to validate the numerical predictions. Results indicate that four design factors positively affect fan performance in terms of flow rate. The guide vane is the most effective design factor to consider for improving fan performance. Further studies are conducted to investigate the detailed effects of the guide vane by varying its install angle, install location, height, and length. These studies determine the optimum design of the guide vane to achieve the highest performance of the fan and the related flow characteristics around the bell mouth.     

Method of internal 3D flow field numerical simulation for hydrodynamic torque converter

To enhance the performance of a hydrodynamic torque converter and thoroughly understand the trait of inside flow, a numerical simulation method of internal 3D flow for the three-element centrifugal hydrodynamic torque converter was systematically researched and expatiated in this paper. First, the internal flow field of each impeller was calculated. The curves that illustrate the relationships between the pressure differences of the inlet and outlet versus flux were drawn. Second, the concurrent working point of each impeller was approximately estimated. Finally, a calculation was performed considering the influence on each impeller. The flow field of a working point was solved by multiple calculations and the actual working condition was gradually determined. The pressure and velocity distributions of the flow field were proposed. The performance parameters of the hydrodynamic torque converter were predicted. The calculation method, and the proposed pressure and velocity distribution of the flow field, have practical significance for the design and improvement of a hydrodynamic torque converter. __________ Translated from Journal of Jilin University (Engineering and Technology Edition), 2006, 36(2): 199–203[译自: 吉林大学学报(工学版)]     

Design of axial fan using inverse design method

The axial fans for cooling condensers were designed by inverse design code TURBOdesign-1. The parameters of the inverse design were set by DOE (design of experiments). By changing the design parameters, such as the distribution of the blade loading, spanwise circulation distribution and stacking, 32 different fan designs were created for the screening of parameters. The overall performance and the local flow field of these fans were computed using a commercial CFD code. The results of the CFD computations were analyzed by DOE. The pressure rise and efficiency were selected as the main responses, and the main effects of the design parameters on the responses were discussed. The main design parameters for the optimum design of the fan were decided from the results of the screening procedure. We designed the optimum axial fan by RSM (response surface method). The design center fan was made by RP (rapid prototype) and the performance was tested using a fan tester based on AMCA standards. These procedures ensured proper screening of parameters and optimum design of the axial fan. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Aeroacoustic computation of cavity flow in self-sustained oscillations

A computational aero-acoustic (CAA) method is used to predict the tonal noise generated from a cavity of automobile door seals or gaps at low flow Mach numbers (M_∞=0.077 and 0.147). In the present method, the acoustically perturbed Euler equations are solved with the acoustic source term obtained from the unsteady incompressible Navier-Stokes calculations of the cavity flow in self-sustained oscillations. The aerodynamic and acoustic fields are computed for the Reynolds numbers based on the displacement thickness, Re_δ*=850 and 1620 and their fundamental mode characteristics are investigated. The present method is also verified with the experimentally measured sound pressure level (SPL) spectra.     

A study on the flow with nonequilibrium condensation in a minimum length nozzle

As recognized previously, a minimum-length nozzle has the smallest possible throat-to-exit length that is still capable of maintaining uniform supersonic flow at the nozzle exit. In the present study, for the flow of moist air through a nearly minimum-length nozzle designed by the method of characteristics, the effects of nonequilibrium condensation on the uniformity of flow properties, the momentum efflux, and the flow distortion at the nozzle exit plane are discussed by experiment and numerical analysis of a third-order Total Variation Diminishing (TVD) finite difference scheme. The onset and zone of nonequilibrium condensation in a minimum-length nozzle are quite different from those of a general convergent-divergent supersonic nozzle. We know that the uniformity of flow properties at the nozzle exit with regard to the flow with nonequilibrium condensation in a minimum-length nozzle cannot be guaranteed. On the other hand, owing to the positions of the onset of condensation at the incident region of expansion waves from the sharp corner just downstream of the nozzle throat, the deceleration gradient and magnitude of heat released from the process of nonequilibrium condensation to the surrounding of ϕ₀=60% are greater than those of ϕ₀=70% in the case of T₀=290K. Furthermore, it has been determined that the decrease in efflux of momentum from the nozzle exit for the stagnation relative humidity of ϕ₀=70%(T₀=290K), which corresponds to the case with nonequilibrium condensation shock, is 6.8% smaller than that of isentropic expansion. This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee Soon-Bum Kwon received his B.S. and M.S. degrees in Mechanical Engineering from Kyungpook National University in 1974 and 1980, respectively, and his Ph.D. degree from Kyushu University in 1987. He is a Professor at the School of Mechanical Engineering at Kyungpook National University. His research interests are compressible gas dynamics and nonequilibrium condensation.     

Numerical study on the effect of the tip clearance of a 100 HP axial fan on the aerodynamic performance and unsteady stall characteristics

In this study, a numerical analysis was conducted to investigate the effect of the tip clearance on the aerodynamic performance, internal flow characteristics, and stall region characteristics of an axial fan. Three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) calculations were conducted with a shear stress transport (SST) turbulence model. Tip clearance ratios of 0, 0.01, and 0.02 were applied to the impeller. As the tip clearance ratio increased, the aerodynamic performance of the axial fan decreased at both the design and the off-design conditions. The correlation between the tip leakage vortex (TLV) and the flow angle of the velocity triangle was presented for the difference in the tip clearance and flow rate. As the flow rate increased, the differences in the aerodynamic performance induced by the tip clearance ratio decreased. As the tip clearance ratio increased, the size of the TLV increased and gradually moved in the circumferential direction to interfere with the main flow at the low flow rate. Meanwhile, the size of the TLV was similar and gradually moved in the axial direction even if the tip clearance ratio increased at the high flow rate. The pressure fluctuations were observed by the fast Fourier transformation (FFT) analysis to compare and analyze internal flow characteristics at the stall region and design point. The static pressure was converted to the appropriate magnitude. The locations of the highest magnitude were shown to be different at the stall region and the design point, respectively.

     

前向多翼式离心风机蜗舌附近流场的PIV试验研究

对前向多翼式离心风机建立了性能及流场测试台位,性能试验重复性良好。用粒子图像速度场仪(Particleimage velocimetry,PIV)技术对蜗舌附近速度矢量场做了详细的变工况测量及分析。结果表明,蜗舌附近的主要流动特征由冲向蜗舌的速度矢量方向及蜗舌周围滞止区的影响范围所决定。小流量时,滞止区影响范围主要在蜗舌间隙流道内,造成速度矢量向叶轮内偏斜,蜗舌下游易形成分离旋涡而恶化;大流量时,滞止区影响范围偏向蜗壳出口流道,蜗舌间隙流动较好。此外,在蜗舌间隙沿轴向不同位置返回蜗壳的流量也不同,这主要与叶片不同段做功能力不同有关。     

离心通风机蜗壳内的流动特征及节能改造试验研究

利用FLUENT软件对G4-73No.8D型离心式风机以及分别加装圆筒型、圆锥筒型防涡圈后的风机内部三维流场进行数值模拟,结果表明,加装防涡圈后的风机蜗壳内部流场流动明显得以改善。对风机在加装防涡圈前后进行的性能试验表明,风机加装圆筒型和圆锥筒型防涡圈后,当相对流量 时,效率平均提高了3.1%和3.48%,验证数值模拟的正确性。理论和试验研究还表明圆锥筒型防涡圈节能效果优于圆筒型防涡圈。     

叶顶间隙变化对轴流风扇性能影响的数值研究

运用三维粘性流动计算软件,对某含叶顶间隙的直叶片轴流风扇进行数值模拟。叶顶间隙按相对间隙进行取值,其大小分别为0、0.5%、1.0%、1.5%和2.0%,其它计算参数不变。通过对计算结果的对比分析,研究叶顶间隙变化对总体性能的影响。结果表明,叶顶间隙变化对轴流风扇性能有较大影响,随着叶顶间隙的增大,其效率、全压减小。     

基于FLUENT数值模拟的离心泵内冰浆两相流流动特性分析

针对冰浆两相流在离心泵的流动特性问题,基于欧拉法建立冰浆Mixture两相流模型,通过FLUENT软件对冰浆流动特性进行数值模拟,得到了在不同流量工况下的离心泵内部压力场、速度场以及冰晶颗粒分布特性.多次数值计算,获得离心泵在输送含冰率为10％的冰浆时的性能特性曲线,并与该离心泵在输送清水时的性能曲线进行了对比分析.研...