Study on Airflow Field of Condensing Zone in Compact Spinning System with Perforated Drum

Negative pressure plays a very important role in compact spinning system.To know airflow field and its distribution is helpful to look into the condensing principle of fiber bundle.Therefore,computational fluid dynamics(CFD)software was used to simulate airflow field in this paper.Airflow velocity distributions both in different fiber layers and under different negative pressures were discussed.The results indicate that airflow velocity in upper layer of the fiber bundle is greater than that in lower layer.Airflow velocities in both X and Y axis directions have a positive correlation with negative pressure.It can provide a theoretical base to make high quality compact yarns in productive practice.

Model of Airflow Field on the Deck for Shipborne Helicopter Flight Dynamics Analysis

For the research of helicopter/ship dynamic interface,the method of combining steady flow and stochastic flow is adopted to establish a flow field model applied to the flight dynamics analysis of shipborne helicopter.The steady flow is calculated by computational fluid dynamics(CFD)method,while the stochastic flow is composed of the compensation velocity derived from ship motion and turbulence above the deck.The accuracy of the proposed flow field model is verified by comparing the helicopter response in the proposed flow field with the results calculated by US Army′s Military Specifications(MIL)model which is commonly used in engineering.Meanwhile,it also shows the proposed flow field model is more appliable to flight dynamics analysis of shipborne helicopter.On that the basis,ship deck flow field is simulated at different sea conditions by adjusting the wind speed on the deck,mother ship movement and shipboard turbulence,etc.And helicopter angular rate response is calculated.The results show that the difference of dynamic stability between helicopter′s roll and pitch leads to the facts that the influence of above factors on the helicopter′s roll angular rate response is greater than that of pitch angular rate,that the frequency and amplitude of mother ship roll motion are much greater than those of pitch motion,and that the disturbance caused by roll motion on the air has greater influence on the helicopter response.The shipboard turbulence is the main disturbance factor that influences helicopter flight stability and its intensity determines the amplitudes of angular rate response.

Numerical Simulation of Airflow Field and Structure Improvement in Engine Compartment of Armored Vehicles with Electric Transmission

When the mechanical drive is changed into the electric transmission,the cooling system of the engine compartment should be altered to meet the new requirement for the increasing in equipment such as electric apparatus.In order to predict and analyze the rationality of cooling system in the virtual engine compartment,the numerical simulation of airflow fields in the engine compartment by using computational fluid dynamics(CFD) technique is necessary.An armored vehicle with electric transmission in the research is taken as the research object.The physical model and mathematical model for the computation of 3D air flow and heat transfer in the engine compartment of an armored vehicle with electric transmission is established.Turbulent flow in the compartment is described by using the standard k-ε two-equation turbulence model.The temperature and velocity fields of 3D air flow in the engine compartment are numerically simulated and analyzed based on different fan's flux.A theoretical basis for determination of the fan's flux is given by the simulation results.The positions of the air-vent shutter are analyzed.The simulation results show that the different positions of the air-vent shutter can lead to different cooling efficiencies.

Influence of the inner tilt angle on downwash airflow field of multi-rotor UAV based on wireless wind speed acquisition system

The downwash airflow field is an important factor influencing the spraying performance of plant protection UAV,and the structural design of rotors directly affects the characteristics of the downwash airflow field.Therefore,in this study,three-dimensional models of a six-rotor UAV with various inner tilt angles were established to simulate and analyze the influence of the inner tilt angle on the downwash airflow field based on the Reynolds average NS equation,RNG k-εturbulence model,etc..On this basis,a wireless wind speed acquisition system using the TCP server was developed to carry out the test through the marked points with real-time detection.The simulation results show that,the variation of inner tilt angles of the six-rotor UAV did not cause significant difference in the time dimension of the downwash airflow field,and with the change of the inner tilt angle from 0°to 8°,the distribution of downwash airflow field tended to obliquely shrink towards the central axis direction,and the amplitude of linear attenuation of airflow speed was also increased,which the difference of attenuation amplitude was 1 m/s.Besides,under the different inner tilt angle,the airflow velocity in“lead in area”was significantly greater than that in the“lead out area”,and the difference of air velocity distribution in space would affect the uniformity of droplet deposition.Through the calibration test,the measurement accuracy error of the developed system was lower than 0.3 m/s,and the adjusted R2 of the calibration fitting equation was higher than 0.99.The test and simulation values at test points from 0.2-2.3 m below the rotors exhibit the same variation trend,and the average relative error at the height of 1.1-2.3 m below the rotors and 0.2-0.8 m near the ground was within 10%and 20%,respectively.The simulation and test results were highly reliable,which could provide basis and reference for the design and optimization of plant protection drones.

Airflow field simulation model building and application for aerobic compost using CFD

Composting is a suitable low-cost strategy to transform animal waste into a stabilized end product,and the airflow field in the pile affects the fermentation states.For piles in the aeration weak zone,anaerobic fermentation may happen as the lack of oxygen.While in practice,due to the extremely low speed and harsh condition,the airflow field was scarcely researched.This study adopted Computational Fluid Dynamics(CFD)to investigate the airflow field in the compost pile.A three-dimensional CFD model was built;the compost pile in this model was simplified as porous media;unstructured mesh was adopted to discretize the geometric model;standard k-εmodel and SIMPLE scheme were employed for numerical methods.The CFD model was validated with the field experiment in the cooling period.Then the model was applied to research the airflow field in the pile with increased pipe diameter.Results showed that it was feasible to investigate the airflow field in the pile with CFD.For boundary conditions in the CFD model,treating the compost pile as a homogeneous porous media is reasonable.The CFD model was successfully validated by the field measurement(the average relative difference between the simulated and measured air speed was within 10%).Airflow in the existing compost pile showed nonuniform distribution with stagnation and vortex zones;the turbulence intensities were 3.57 and 1.43 for the airflow in the pile and the reactor,respectively.When pipe diameter increased,the airflow distribution uniformity in the pile was improved significantly.With diameter raising to 0.04 m,the turbulence intensity decreased to 1.54 and 0.42 for the airflow in the pile and the reactor,respectively.The CFD model developed in this research can provide qualitative and quantitative analyses of the airflow field in compost piles,and can be a theoretical basis for the aeration system design.

Airflow characteristics by air curtain jets in full-scale room

A new air distribution pattern,air curtain jet ventilation was presented.The ventilation or airflow patterns and the air velocity produced by air curtain jet were investigated in detail.To identify the airflow characteristics of this novel air curtain jet ventilation system,a full-scale room was used to measure the jet velocity with a slot-ventilated supply device,with regards to the airflow fields along the vertical wall as well as on the horizontal floor zones.The airflow fields under three supply air velocities,1.0,1.5 and 2.0 m/s,were carried out in the full-scale room.The experimental results show the velocity profiles of air distribution,the airflow fields along the attached vertical wall and the air lake zones on the floor,respectively.The current experimental research is helpful for heating,ventilation and air conditioning(HVAC) engineers to design better air distribution in rooms.

Study on application and numerical simulation of the airflow temperature distribution rule in drifting tunnel

According to the law of conservation in the state of turbulent flow, the differential equation describing the airflow temperature distribution in drifting tunnel is derived, By theoretical analysis and field measurement of the airflow and thermal process in mine, theoretical analysis and systematic flow are developed. By PHONENICS program, the numerical simulation is processed, and the changing rule of airflow temperature with various parameters in drifting tunnel is derived. The airflow temperature in drifting tunnel decreases as the airflow velocity increases in a way of negative power exponent, and elevates linearly as the temperature of the incoming airflow elevates.

基于机器学习方法的三维气流组织温度场重构

从局部离散流场数据点重构全局流场信息对数据中心机房的节能节碳具备重要的研究意义。基于局部散点对数据中心进行气流组织温度场快速重构,可有效降低数据中心总能耗。主要通过发展一种基于多特征输入的三维U形神经网络架构(U-net),利用布设在数据中心机房的温度传感器数据值进行气流组织温度场重构。并研究了在不同学习率与数据集大小的设置下,该机器学习模型的训练预测能力。对比结果表明:不同学习率对于模型训练的结果有较大影响,应通过预实验选取最佳学习率。在同等条件下,应优先选取较大的数据集进行训练,便于提取高维物理特征。

烟草喷雾机气流场数值仿真及试验验证

为了探究烟草喷雾机风送系统气流分布情况,利用数值仿真与试验验证相结合的方法分析气流场分布规律。结果表明:1)该喷雾机气流场中气流在喷筒内导流柱两侧分布均匀,喷筒出风口截面处气流分布的仿真结果与实测结果之间相对误差较小且分布趋势一致,证明了仿真模型的合理性和有效性;2)风速与测量位置到出风口截面距离的线性回归方程为y=13.29-9.49x,相关系数为0.721。仿真及试验结果为后续风送系统的优化设计提供了参考。

Experimental and numerical simulation study on forced ventilation and dust removal of coal mine heading surface

In order to study the problems of unreasonable airflow distribution and serious dust pollution in a heading surface,an experimental platform for forced ventilation and dust removal was built based on the similar principles.Through the similar experiment and numerical simulation,the distribution of airflow field in the roadway and the spatial and temporal evolution of dust pollution under the conditions of forced ventilation were determined.The airflow field in the roadway can be divided into three zones:jet zone,vortex zone and reflux zone.The dust concentration gradually decreases from the head to the rear of the roadway.Under the forced ventilation conditions,there is a unilateral accumulation of dust,with higher dust concentrations away from the ducts.The position of the equipment has an interception effect on the dust.The maximum error between the test value and the simulation result is 12.9%,which verifies the accuracy of the experimental results.The research results can provide theoretical guidance for the application of dust removal technology in coal mine.

果蔬隧道式气流冲击干燥流场模拟及其设备结构优化

为解决隧道式气流冲击干燥设备中风速流场不均匀的问题,利用计算流体动力学对气流冲击干燥过程的流场进行模拟分析,提出2种改进方案,并且每种方案选择9组模型,通过对比分析每组模型的速度均匀性和流场分布情况,以速度不均匀性为指标,得到结构参数为高度H=630 mm、半径R=60 mm圆柱扰流装置,并在此基础上,进行气流分配口大小调整,将上层和下层气流分配口调整为25 mm,中层气流分配口调整为20 mm的模型为最优结构。最优结构气流分配口速度不均匀系数减小到20.4%,物料层截面速度不均匀系数减小到16.89%,极大地改善气流冲击干燥的均匀性。对改进的模型进行试验验证,模拟值与试验测量值的相对误差均在11%以内。研究为相关干燥设备的结构优化提供参考。

低气压直流转换开关开断能力研究

直流转换开关被广泛应用于特高压直流输电工程,用于系统运行方式的切换。其多采用无源自激振荡的技术路线,具有结构简单、性能可靠等优点。该文以直流转换开关为研究对象,通过SF6气体低气压特性分析,结合直流转换开关开断过程灭弧室的气流场仿真分析结果,优化气流通道,设计出适用于低气压环境的大容量开断装置。采用了低频振荡电流法等效直流电源进行直流转换开关的电流转换能力验证,分别在不同电流、不同气体压力时进行电流转换试验。由试验结果可知,随着开断装置充气压力的降低,电流转换的能力下降率达到10%~25%,且燃弧时间较长。通过仿真和试验研究,为低气压条件下直流转换开关的设计和电流转换能力评估奠定了基础。

外场气流场前端测量误差统计方法探讨

外场测试的随机性和有效性需要适用的统计方法进行观察,外场气流场测试通常用于舰船等平台稳定运行时的气流场特性研究,为明确每个测试工况的初始条件,需要对平台的前端流场进行测量,作为对应工况的参考性输入。首先,对测量误差典型方法进行对比,然后利用超声波风速仪作为测试工具,借鉴气象计量的相关标准,提出了外场气流场前端测量误差参数统计的方法,模拟了舰船外场气流场测试的3个典型工况并进行数据采集,对测量数据误差进行处理分析,置信概率大于50%,初步验证了该方法的有效性。

短棒黑木耳负压采收机内部流场模拟与设备优化

为分析箱体结构对短棒黑木耳负压采摘机内部流场的流速变化、采摘头吸风口处的压力、箱体内部涡旋情况、进出风口风压压差的影响,建立不同吸风口位置及采摘管直径的3D模型,基于Fluent软件对短棒黑木耳负压采摘机内部流场进行流场模拟。根据迹线图分析收集箱出风口处于不同位置时,箱体内涡旋情况;研究设备内部流场压力云图与矢量图,分析不同采摘管直径下管道内流速变化、箱体内平均流速值与采摘口所受风压情况。为验证数据可靠性,设置标准吸力试验。试验结论与流场模拟结果相符,验证流场数值模拟的可靠性。数值仿真结果表明,螺纹管直径和出风口高度对负压采摘机内部流场影响显著。螺纹管直径越大,气流场压降越大。且随着螺纹管的内径增大,管道内的气流速度衰减越快,箱体内气流涡旋现象越严重。吸风口位置会影响箱体内涡旋情况。出风口离收集箱顶部越近,涡旋现象越弱。综合考虑,较优的螺纹管直径为58 mm,较合适的吸风口位置为出风口圆心距离箱体顶部60 mm。

一器三行小青菜精量排种器设计与优化

为改善我国传统的单行和双行播种模式所面临的播种效率低下的问题,以“上海矮箕”小青菜种子为研究对象,设计一种新型的一器三行精量排种器,并对排种器的工作原理进行分析。通过相关数学理论计算出所设计排种器关键部件的相关参数。利用FLUENT软件对排种器内部气流场进行分析,确定最佳的吸孔数目。将负压、排种盘角速度以及吸孔锥角作为试验因素,以排种器进行排种时的合格率以及漏播率作为性能指标,开展CCD二次旋转正交组合试验。当负压为-2.16 kPa,排种盘角速度为29.43 r/min,吸孔锥角为61.51°时,内圈合格率为95.12%,漏播率为3.67%,中圈合格率为94.68%,漏播率为3.12%,外圈合格率为94.24%,漏播率为2.58%。进行台架试验和田间试验验证所得最佳组合参数的合理性。

基于Ω漩涡识别方法探究转杯凝聚槽漩涡对纺纱质量的影响

为了更为准确地识别与分析转杯纺转杯内复杂多变流场中的涡流情况,提出了一种结合Ω漩涡识别方法和图像处理的漩涡识别技术。文章对Fluent仿真得到的转杯流场进行了分析,得到了凝聚槽平面的漩涡数量与面积,并进一步探究了凝聚槽内漩涡分布对纱线质量的影响。结果表明:Ω漩涡识别方法对凝聚槽漩涡有较好的捕捉效果,经过图像处理后可以定量化分析转杯内部气流流场的涡流情况;凝聚槽内漩涡主要分布在输纤通道出口处以及背后气流交汇处;随着转速的提升,转杯凝聚槽内细小漩涡面积增加,不利于纱线聚合;较大直径转杯凝聚槽部位漩涡面积更小,有利于纤维聚合。文章通过图像识别的方式探究转杯内流场的漩涡分布特征,为优化转杯纺结构提供了一定理论支持。

转杯纺分梳排杂区气流场的多维数值模拟对比

为探讨转杯纺分梳排杂区二维与三维模型气流场数值模拟结果的准确度与差异性,采用COMSOL仿真模拟软件建立分梳排杂区的二维与三维几何模型,对气流场进行数值模拟并进行比较。结果表明:与二维模型模拟结果相比,三维模型输纤通道出口处速度高,分梳腔速度、压强与湍动能分布更均匀,且排杂区的气流与湍动能分布结果更加准确;引入杂质颗粒后的运动结果也证明,三维模型中大部分杂质颗粒随气流运动及时排除,仅有少部分杂质进入输纤通道内,对流场细节和颗粒分布情况的模拟展现得更加准确直观,适合指导实际生产与优化转杯纺机构的设计。

船舶机舱气流组织及温度场优化设计

为解决原方案机舱空气流动存在死角和局部过热区的问题,综合考虑进风量、甲板开口、机舱设备和管路布置、风管开口位置和开口数的影响,对某大型散货船机舱通风方案进行优化,并进行有限元仿真。结果表明:在相同通风配置条件下,优化方案的机舱整体区域温度为48℃,相较原方案降低21%,其气流组织流通情况也得到显著提升。研究成果可为船舶机舱通风方案设计提供一定参考。

5XZ-10型比重式种子分选机中离心风机流场研究

利用空气动力学原理进行种子分选,空气流场的分布至关重要。针对农业机械装置中气流均匀性问题,以5XZ-10型比重式种子分选机中离心风机为原型,利用Solidworks软件建立离心风机几何模型,运用Fluent软件对离心风机内部流场及出口流场进行数值模拟计算。通过仿真试验得到离心风机流场分布,对风机出口速度分布云图及矢量图结果进行分析,发现风机内部流场受到机械结构的干扰,气流在风机出口界面分布较不均匀,提出了离心风机流场优化措施,包括双叶轮双入口单出口离心风机入口增设集流器、对固定盘与叶轮的连接进行密封、风机出口采用钢板网对出口气流进行均匀性改善。在距离风机出口上方0.13 m处安装钢板网,增设钢板网后风机出口气流均匀性指数由0.88提升至0.90,提升率2.27%,解决了风机提供的气流流经5XZ-10型比重式种子分选机筛面时的均匀性问题。

喷射成形中的下级雾化器参数优化

针对喷射成形锭坯的孔隙较大问题,研究了下级雾化器参数优化策略。基于下级雾化器参数对气流场的影响规律控制熔滴的状态变化,以此来减小锭坯的孔隙。针对不同的下级雾化器的顶角、喷嘴直径和雾化气体压力,分析气流场的变化,得到这3个参数对气流场的影响规律,进行喷射成形实验。结果表明:在下级雾化器参数优化后,熔滴的雾化效果明显提高,且采用优化后的下级雾化器参数制备的铝合金锭坯孔隙更小。