压缩空气涡管在工程中的应用

介绍一种新的冷却装置“压缩空气涡管”.分析了压缩空气进入装置后,如何将其分离成冷、热气流的全过程和机理.通过例举几种利用该装置产生的冷气流,在工程中的应用典范,从而说明,在一些特定的加工环境中,这种被降温的冷气可完成加工中需要散热、冷却,而又不能或不允许使用液体介质的工作.

基于单片机的涡卷式空压机电控系统设计

涡卷式空气压缩机是一种新型空气压缩机,具有噪声低、体积小、可靠性好等特点。本文提出了一种基于ATMEL89C52单片机的涡卷式空气压缩机电气控制系统的实现方案,详细说明了总体方案设计、硬件设计与软件设计,并给出了关键元器件的选型。实际结果表明:该系统具有可靠性好、控制精度高、操作简便、配置灵活、直观的故障指示及完善的自保护等特点,完全满足了涡卷式空气压缩机现场控制的要求,是涡卷式空气压缩机的理想配套产品。

离心式喷嘴雾化特性实验研究与数值模拟

为研究气液两相流体在离心喷嘴中的流动机理和雾化特性,设计制作了6种可视化的双旋流槽离心喷嘴,采用高速摄像系统,研究喷嘴内部及外部的流动情况。建立了离心式喷嘴内部流动的VOF(Volume of Fluid)模型,基于Fluent软件进行数值模拟,获得了喷嘴内部流动的密度场以及喷口处速度特性。结果表明,进口为纯水时喷嘴内部存在稳定的圆柱状空气核,且喷雾为空心雾锥;当进口为气液两相时喷嘴内部存在圆锥状气液混合区,且喷雾为实心雾锥;模拟结果与实验结果吻合较好。

一种变几何特性离心喷嘴的结构设计与流场分析

为适应植保作业变量喷雾需求,设计了一种变几何特性离心喷嘴.通过Fluent软件的VOF模型对喷嘴内外流场进行三维全尺寸数值模拟,研究了喷嘴稳定喷雾时内流场径向分布特性及轴向变化规律,分析了喷嘴内部形成空气涡的喷口旋流条件;通过对外流场模拟和试验数据采用数字图像处理求取喷雾角,并结合经验公式比较分析了计算结果的准确性.该研究为优化喷嘴构型和连续变量喷雾装置的研发提供了理论基础.

核援救舰船救生通道的防核污染方法研究

为了对开展核援救活动的涉核舰船进行保护,需要研究救生通道的核防护问题。分别分析了防护区、救生通道的现状、存在的问题,估算了隔离门、空气幕以及长通道空气涡塞系统等三种方法在人通过通道时所附加的新风需求量,分析了上述三种方法的防护能力,并通过数值仿真、实物试验验证长通道空气涡塞系统不妨碍交通,对空气污染的阻隔能力强,是一种有前途的隔离核污染方法。

基于VOF方法的多孔陶瓷快速成型喷嘴流场数值分析

为改善多孔陶瓷坯体中泥料开裂、分层现象,利用VOF方法和层流模型,以等效的二维网格模型对多孔陶瓷快速成型喷嘴流场进行数值分析,分析泥料进口速度对速度分布、压力分布和泥料体积分数的影响。结果表明：泥料进口速度为0.001 m/s时,喷嘴内速度分布均匀,没有出现空气涡;进口速度为0.002 m/s时,喷嘴内部存在压力差,在喷嘴轴线1/5处出现约占喷嘴总面积0.5%的空气涡;进口速度为0.003 m/s时,空气涡约占喷嘴总面积6%;数值分析和实验结果基本吻合,误差在12.5%以内,在用快速成型技术制备多孔陶瓷时,泥料进口速度需控制在临界值0.002 m/s以下。

Study on Calculations of Humidification Tower with Humid Air Turbine Cycle at High Temperature and Pressure

Humidification is an important step in humid air turbine system. The calculation on humidification is carried out at 423.15—573.15K, 5—15MPa. The results suggest that to produce high-enthalpy moist air, high water temperature and large water flow are needed. The water temperature is the most sensitive parameter to the humidification tower. And it is better for the humidification tower to work at temperature higher than 523 K when the system pressure is higher than 5 MPa. The comparison between the model used in this paper and ideal model shows that the ideal model can be used in simulation to simply the calculation when the temperature is lower than 473 K and pressure is lower than 5 MPa.

A Numerical Study of Mesoscale Vortex Formation in the Midlatitudes:The Role of Moist Processes

In this study, a three-dimensional mesoscale model was used to numerically simulate the well-known "98.7" heavy rainfall event that affected the Yangtze Valley in July 1998. Two experiments were conducted to analyze the impact of moist processes on the development of meso-β scale vortices(MβV) and their triggering by mesoscale wind perturbation(MWP). In the experiment in which the latent heat feedback(LHF) scheme was switched off, a stable low-level col field(i.e., saddle field—a region between two lows and two highs in the isobaric surface) formed, and the MWP triggered a weak MβV. However, when the LHF scheme was switched on as the MWP was introduced into the model, the MβV developed quickly and intense rainfall and a mesoscale low-level jet(mLLJ) were generated. The thickness of the air column and average temperature between 400 and 700 hPa decreased without the feedback of latent heat, whereas they increased quickly when the LHF scheme was switched on, with the air pressure falling at low levels but rising at upper levels. A schematic representation of the positive feedbacks among the mesoscale vortex, rainfall, and mLLJ shows that in the initial stage of the MβV, the MWP triggers light rainfall and the latent heat occurs at low levels, which leads to weak convergence and ageostrophic winds. In the mature stage of the MβV, convection extends to the middle-to-upper levels, resulting in an increase in the average temperature and a stretching of the air column. A low-level cyclonic circulation forms under the effect of Coriolis torque, and the m LLJ forms to the southeast of the MβV.

Numerical Investigations on the Aerodynamic Performance of Wind Turbine： Downwind Versus Upwind Configuration

Although the upwind configuration is more popular in the field of wind energy, the downwind one is a promising type for the offshore wind energy due to its special advantages. Different configurations have different aerodynamic performance and it is important to predict the performance of both downwind and upwind configurations accurately for designing and developing more reliable wind turbines. In this paper, a numerical investigation on the aerodynamic performance of National Renewable Energy Laboratory （NREL） phase V1 wind turbine in downwind and upwind configurations is presented. The open source toolbox OpenFOAM coupled with arbitrary mesh interface （AMI） method is applied to tackle rotating problems of wind turbines. Two 3D numerical models of NREL phase VI wind turbine with downwind and upwind configurations under four typical working conditions of incoming wind velocities are set up for the study of different unsteady characteristics of the downwind and upwind configurations, respectively. Numerical results of wake vortex structure, time histories of thrust, pressure distribution on the blade and limiting streamlines which can be used to identify points of separation in a 3D flow are presented. It can be concluded that thrust reduction due to blade-tower interaction is small for upwind wind turbines but relatively large for downwind wind turbines and attention should be paid to the vibration at a certain frequency induced by the cyclic reduction for both configurations. The results and conclusions are helpful to analyze the different aerodynamic performance of wind turbines between downwind and upwind configurations, providing useful references for practical design of wind turbine.

PRELIMINARY STUDY ON RELATIONSHIP BETWEEN DOUBLE VORTICES SELF-ORGANIZATION AND TYPHOON FORMATION IN BAROCLINIC ENVIRONMENT

The relationship between the self-organization of double vortices （SODVs） and the formation of typhoons was discussed based on six numerical experiments with the Fifth-Generation National Center for Atmospheric Research/Penn State Mesoscale Model （MM5） and further discussion was made with a real typhoon case. The results showed that there is a critical distance dc for SODVs in baroclinic atmosphere. When the distance between separated vortices is smaller than or equal to d~, the double vortices self-organize into a typhoon-like vortex with two spiral bands. But the double vortices cannot have such organization if the distance between them is larger than de. The value of dc is about 380 km in the context of ideal conditions in this paper, larger than that achieved in a barotropic model. A typical typhoon case in 2005 （Haitang） was selected to verify the above-mentioned conclusions. It was found that the SODV is one of the important and typical ways for the formation of typhoons.

Three-Dimensional Numerical Investigation of the Separation Process in a Vortex Tube at Different Operating Conditions

Air separators provide safe, clean, and appropriate air flow to engines and are widely used in vehicles with large engines such as ships and submarines. In this operational study, the separation process in a Ranque-Hilsch vortex tube cleaning （cooling） system is investigated to analyze the impact of the operating gas type on the vortex tube performance; the operating gases used are air, nitrogen, oxygen, carbon dioxide and nitrogen dioxide. The computational fluid dynamic model used is equipped with a three-dimensional structure, and the steady-state condition is applied during computations. The standard k-c turbulence model is employed to resolve nonlinear flow equations, and various key parameters, such as hot and cold exhaust thermal drops, and power separation rates, are described numerically. The results show that nitrogen dioxide creates the greatest separation power out of all gases tested, and the numerical results are validated by good agreement with available experimental data. In addition, a comparison is made between the use of two different boundary conditions, the pressure-far-field and the pressure-outlet, when analyzing complex turbulent flows in the air separators. Results present a comprehensive and practical solution for use in future numerical studies.

Functional design of wind turbine airfoils based on roughness sensitivity characteristics

To improve aerodynamic performance of wind turbine airfoils,the shape profile characteristic of the airfoil is investigated.Application of conformal transformation,one functional and integrated expression of wind turbine airfoils is presented.Using the boundary layer theory,the aerodynamic model with roughness of wind turbine airfoils is introduced by studying flow separation around the airfoil.Based on the shape expression and aerodynamic performance of airfoils,the function design of wind turbine airfoils is carried out that the maximum lift-drag ratio and low roughness sensitivity are designed objects.Three wind turbines airfoils with different thickness are gained which are used at tip part of blades.As an example,the aerodynamic performance of one designed airfoil with relative thickness of 15%is simulated in different conditions of clean surface,rough surface,laminar flow and turbulent flow.The comparison of aerodynamic performance between the designed airfoil and one popular NACA airfoil is completed which can verify the better performance of the designed airfoil and reliability of the designed method.

Large-eddy Simulation of Ethanol Spray-Air Combustion and Its Experimental Validation

Large-eddy simulation of spray combustion is under its rapid development.Different combustion models were used by different investigators.However,these models are less validated by detailed experimental data.In this paper,large-eddy simulation(LES)of ethanol spray-air combustion was made using an Eulerian-Lagrangian approach,a subgrid-scale kinetic energy stress model,and a filtered finite-rate combustion model,neglecting the sub-grid scale reaction rate.The simulation results are compared with experimental dada in the literature and validated in detail.The LES obtained statistically averaged gas temperature is in much better agreement with the experimental results than Reynolds averaged(RANS)modeling using the most complex probability density function(PDF)equation combustion model.The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map,indicating that the droplets are concentrated in this shear region.The instantaneous temperature,oxygen and carbon dioxide concentration maps show the close interaction between the coherent structures and the combustion reaction.

Investigation of the Aerodynamic Character in Turbine Cascades with Aft-loaded Profile

For evaluate the aerodynamic character of the turbine cascades which have the aft-loaded profile, the experimental investigation was carried out on the low speed annular wind tunnel. And the detailed measurements of the aerodynamic parameters were made from upstream to downstream of the two type turbine cascades, the one is the conventional straight blades cascade, the other is the curved blades cascades. The static pressure distributions on the endwall and the blade surface were also carried out. The influence of the aft-loaded profile and the curved blade on the development of loss and the pressure distribution was discussed, and analyses the different flow phenomena and mechanism in two type turbine cascades.

Experimental Investigation on Turbulent Convection in Solar Air Heater Channel Fitted with Delta Winglet Vortex Generator

The paper presents an experimental study on the heat transfer and flow friction characteristics in a solar air heater channel fitted with delta-winglet type vortex generators （DWs）. The experiments are conducted by varying the airflow rate for Reynolds number in the range of 5000 to 24000 in the test section with a uniform heat-flux applied on the upper channel wall. Firstly, the DW pairs are mounted only at the entrance of the lower wall of the test channel （called DW-E） to create multiple vortex flows at the entry. The effect of two transverse pitches （Re= Pt/H= 1 and 2） at three attack angles （a= 30°, 45° and 60°） of the DW-E with its relative height, b/H= 0.5 （half height of channel） is examined. Secondly, the 30° DWs with three different relative heights （blH = 0.3, 0.4 and 0.5） are placed on the upper wall only （absorber plate, called DW-A） of the test channel. The experimental result reveals that in the first case, the 60° DW-E at Rp = 1 provides the highest heat transfer and friction factor while the 30° DW-E at Rp = 1 performs overall better than the others. In the second case, the 30° DW-A at b/H= 0.5 yields the highest heat transfer and friction factor but the best thermal performance is found at b/H = 0.4.

Effect of blade pitch angle on aerodynamic performance of straight-bladed vertical axis wind turbine

Wind energy is one of the most promising renewable energy sources, straight-bladed vertical axis wind turbine(S-VAWT) appears to be particularly promising for the shortage of fossil fuel reserves owing to its distinct advantages, but suffers from poor self-starting and low power coefficient. Variable-pitch method was recognized as an attractive solution to performance improvement, thus majority efforts had been devoted into blade pitch angle effect on aerodynamic performance. Taken into account the local flow field of S-VAWT, mathematical model was built to analyze the relationship between power outputs and pitch angle. Numerical simulations on static and dynamic performances of blade were carried out and optimized pitch angle along the rotor were presented. Comparative analyses of fixed pitch and variable-pitch S-VAWT were conducted, and a considerable improvement of the performance was obtained by the optimized blade pitch angle, in particular, a relative increase of the power coefficient by more than 19.3%. It is further demonstrated that the self-starting is greatly improved with the optimized blade pitch angle.

Impeller modeling and analysis based on UG NX/KF and Fluent

Parametric modeling of the impeller which drove a small wind device was built by knowledge fusion technology.NACA2410 airfoil blade was created by KF language.Using technology of UG/KF secondary development for the automatic modeling of wind turbine blade,the program can read in the airfoil data files automatically and the impeller model entity can be generated automatically.In order to modify the model,the aerodynamic characteristics of the impeller were analyzed for getting aerodynamic parameters by Fluent.The maximum force torch and best parameters of impeller were calculated.A physical prototype impeller was manufactured and the correctness of the design was verified,and the error of force torch between simulation and experimental results is about 10%.Parameterization design of the impeller model greatly improves the efficiency of modeling and flexibility of the CAD system.

Numerical simulation of 3D viscous flow field of air cooled turbine blades with coolant mixing

To improve thrust and reduce oil consumption of aero-engines, the temperature at turbine inlet is becoming higher and higher, which leads to heavy thermal load of vanes. To efficiently cool the vanes, the mass of coolant with its maximum gas mass flow exceeding to 20% of main stream, has to be increased. In the pres- ent paper, a two-stage turbine with and without coolant mixing was simulated by CFX-TASCflow. Simulation resuits indicate that the flow field structure with coolant is obviously different from that without coolant, and the former has characteristics of lower-speed main flow, reduced mach number, weaker shock intensity and decreased stage efficiency.

Parametric geometry representations for wind turbine blade shapes

Based on the Joukowsky transformation and Theodorsen method, a novel parametric function （shape function） for wind turbine airfoils has been developed. The airfoil design space and shape control equations also have been studied. Results of the analysis of a typical wind turbine airfoil are shown to illustrate the evaluation process and to demonstrate the rate of convergence of the geometric characteristics. The coordinates and aerodynamic performance of approximate airfoils is rapidly close to the baseline airfoil corresponding to increasing orders of polynomial. Comparison of the RFOIL prediction and experimental results for the baseline airfoil generally show good agreement. A universal method for three-dimensional blade integration-＂ Shape function/Distribution function＂ is presented. By changing the parameters of shape function and distribution functions, a three dimensional blade can be designed and then transformed into the physical space in which the actual geometry is defined. Application of this method to a wind turbine blade is presented and the differences of power performance between the represented blade and original one are less than 0. 5%. This method is particularly simple and convenient for bodies of streamline forms.

A New Unsteady Fluid Network Approach to Simulate the Characteristics of the Air System of a Gas Turbine System

In this paper, a novel unsteady fluid network simulation method to compute the air system of jet engine was coded to predict the characteristics of pressure, temperature and mass flow rate of the flow and the temperature of the solid in the gas turbine engine. The fluid and solid areas are divided into the network comprised of branches and nodes, and the method solves transient mass, energy conservation equations at each node and momentum conservation equation at each branch by a newly deduced numerical method. With this method, to simulate complicated fluid and solid system in short time becomes possible. To verify the code developed, it has been applied to simulate a gas turbine model against the widely used commercial software Flowmaster. And the comparisons show that the two are in good agreement. Then the verified program is applied to the prediction of the characteristics of a designed turbine disk and air-cooling system associated to it, and useful information is obtained.