Aerodynamic drag reduction of heavy vehicles using append devices by CFD analysis

Improving vehicle fuel consumption,performance and aerodynamic efficiency by drag reduction especially in heavy vehicles is one of the indispensable issues of automotive industry.In this work,the effects of adding append devices like deflector and cab vane corner on heavy commercial vehicle drag reduction were investigated.For this purpose,the vehicle body structure was modeled with various supplementary parts at the first stage.Then,computational fluid dynamic(CFD) analysis was utilized for each case to enhance the optimal aerodynamic structure at different longitudinal speeds for heavy commercial vehicles.The results show that the most effective supplementary part is deflector,and by adding this part,the drag coefficient is decreased considerably at an optimum angle.By adding two cab vane corners at both frontal edges of cab,a significant drag reduction is noticed.Back vanes and base flaps are simple plates which can be added at the top and side end of container and at the bottom with specific angle respectively to direct the flow and prevent the turbulence.Through the analysis of airflow and pressure distribution,the results reveal that the cab vane reduces fuel consumption and drag coefficient by up to 20 % receptively using proper deflector angle.Finally,by adding all supplementary parts at their optimized positions,41% drag reduction is obtained compared to the simple model.

New endoscopes and add-on devices to improve colonoscopy performance

Colonoscopy is the gold standard for colorectal cancer prevention; however, it is still an imperfect modality. Precancerous lesions can be lost during screening examinations, thus increasing the risk of interval cancer. A variety of factors either patient-, or endoscopist dependent or even the procedure itself may contribute to loss of lesions. Sophisticated modalities including advanced technology endoscopes and add-on devices have been developed in an effort to eliminate colonoscopy's drawbacks and maximize its ability to detect potentially culprit polyps. Novel colonoscopes aim to widen the field of view. They incorporate more than one cameras enabling simultaneous image transmission. In that way the field of view can expand up to 330°. On the other hand a plethora of add-on devices attachable on the standard colonoscope promise to detect lesions in the proximal aspect of colonic folds either by offering a retrograde view of the lumen or by straightening the haustral folds during withdrawal. In this minireview we discuss how these recent advances affect colonoscopy performance by improving its quality indicators(cecal intubation rate, adenoma detection rate) and other metrics(polyp detection rate, adenomas per colonoscopy, polyp/adenoma miss rate) associated with examination's outcomes.

新型高速列车风阻制动装置气动特性及制动性能研究

为实现高速列车风阻制动系统在高速运行或紧急制动阶段,满足双向多模式多级选择制动,同时具备优良的空气动力学特性,以设计速度为400 km/h的高速动车组为参考,提出“窗形”风阻制动装置及其改进型设计方案,并进行气动分析与制动性能研究。以改进型“窗形”风阻制动装置前后两排风阻制动板纵向中间补偿板有效长度为变量,建立计算流体动力学模型,研究发现:当中间补偿板有效长度增加至1.75 m制动工作时,双排风阻制动板整体产生的气动阻力约为4.37 kN,气动阻力系数为1.08,附加气动升力约为0 kN,阻力贡献与单排风阻制动板产生的制动力基本相当,前排对后排的直接干涉系数为临界值1;当中间补偿板有效长度为2 m时,计算风阻制动板纵向对称面内距离外围轮廓100 mm处空间范围的声压级达102.20 dBA,对应声功率为2.82×10^(-2)W/m^(3);当每节车辆均布1组改进型“窗形”风阻制动装置时,其所能提供的有效风阻制动力为28.7 kN,风阻瞬时减速度为0.0674 m/s^(2),为列车紧急制动减速度的13%,同时大于1级常用制动减速度,阻力贡献明显。

Aerodynamic performance enhancement of co-flow jet airfoil with simple high-lift device

The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing.Computations have been accomplished by an in-house-programmed Reynoldsaveraged Navier-Stokes solver enclosed by k-ωshear stress transport turbulence model.Three crucial geometric parameters,viz.,injection slot location,suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift,drag,power consumption and equivalent lift-to-drag ratio.Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack.The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle.The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio.Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain,meanwhile,carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.

Aerodynamic optimization using passive control devices near the bogie cabin of high-speed trains

Bogies are responsible for a significant amount of aerodynamic resistance and noise,both of which negatively affect high-speed train performance and passenger comfort.In the present study,the passive control method is applied in designing the bogie cabins of a high-speed train to improve its aerodynamic characteristics.Two passive control measures are introduced,namely,adding a spoiler and creating diversion grooves near the bogie cabins.Furthermore,the aerodynamic and aeroacoustic characteristics of a high-speed train operating at 350 km/h under different control strategies are numerically investigated using the improved-delayed-detached-eddy simulation(IDDES)and the acoustic finite element method(FEM).The impacts of passive control devices on drag reduction,slipstream,and aerodynamic noise are presented and discussed.Numerical results reveal that the passive control devices have a major effect on the slipstream around the train.The amplitude of the fluctuating pressure is higher in the first half of the train than in the second half.The first bogie has the maximum amplitude of the acoustic pressure for both the train with and without passive devices.In the far field,the spoiler installation and placement of the diversion grooves in the front of the bogie cabin can significantly reduce aerodynamic drag and noise.Hence,as shown in this study,using passive control methods to improve the aerodynamic and aeroacoustic properties of high-speed trains can be a viable option.

A novel hybrid method for aerodynamic noise prediction of high-lift devices

Aerodynamic noise of High-Lift Devices(HLDs)is one of the main sources of airframe noise,and has immediate impacts on the airworthiness certification,environmental protection and security of commercial aircraft.In this study,a novel hybrid method is proposed for the aerodynamic noise prediction of HLD.A negative Spalart-Allmaras(S-A)turbulence model based Improved Delayed Detached Eddy Simulation(IDDES)method coupling with AFT-2017b transition model is developed,in order to elaborately simulate the complex flow field around the HLD and thus obtain the information of acoustic sources.A Farassat-Kirchhoff hybrid method is developed to filter the spurious noise sources caused by the vortex motions in solving the Ffowcs Williams-Hawkings(FW-H)equation with permeable integral surfaces,and accurately predict the far-field noise radiation of the HLD.The results of the 30P30N HLD indicate that,the computational Sound Pressure Levels(SPLs)obtained by the Farassat-Kirchhoff hybrid method conform well with the experimental ones in the spectrum for the given observation point,and are more accurate than those obtained by the Farassat 1A method.Based on the hybrid method,the acoustic directivity of the HLD of a commercial aircraft is obtained,and the variation of the SPLs in the spectrum with the deflection angle of the slat is analyzed.

露天试车台侧风装置气动特性数值模拟

为了探究露天试车台侧风装置的气动流场特性,采用商用软件构建了侧风装置的全3维数值模型,完成了侧风装置气动特性的数值模拟。结果表明:安装在靠近侧风装置壁面附近的风机对风场边界产生影响,最中间1台风机排出的气流直接影响速度核心区中心风场,临近最中间水平方向两侧的2台风机排出的气流对关注截面偏离z中心轴线±0.25D位置产生影响;气流从侧风装置排出后可发现核心流速区、掺混区和低速扰动区3个区域,核心流速区内的气流变化平稳,未见大的波动;在以发动机进气轴线为中心d=0.8D直径范围内,随着风速的增大,最大流速差逐渐增大,速度不均匀度逐渐减小。研究结果可为发动机开展侧风试验提供理论和技术基础。

二级活塞式弹射机构动态仿真与分析

运用经典内弹道和气体动力学理论 ,建立了二级活塞式抛放弹弹射机构的数值计算模型 ,对某型号二级活塞式弹射机构工作的全过程进行了模拟计算 ,分析了不同参数对其弹射效果的影响 .计算结果与实验结果相符 .

新型气力精密排种器的空气动力学原理

提出一种具有控制充种室种子群结构的新型气力精密排种器的空气动力学原理。采用Ｋ－ε湍流模型和ＳＩＭＰＬＥ算法，预测了充种室的流场，数值计算结果和实验相附。数值预测出在充种室的不对称射流产生了一个有利于改善充种和清种的回流区。这种排种器已成功地用于精密播种机上。

高速列车车体气动载荷疲劳强度试验装置研究

研制车体交变气动载荷试验装置,利用该装置对新造车体进行疲劳强度试验,讨论车体交变气动载荷疲劳试验加载方法、压力、压力波形与周期、加载次数等参数,并完成车体交变气动载荷疲劳试验装置方案及数据采集系统方案设计;将合武铁路现场测得的CRH2型动车组以250 km/h速度过隧道时车内外压力差曲线与该试验装置测得的压力曲线进行比较。研究结果表明:车内外压力差曲线与该试验装置测得的压力曲线基本吻合,该试验装置可真实模拟列车高速通过隧道时车体承受的交变气动载荷,为研究新造高速列车车体在交变气动载荷作用下的疲劳强度特性提供了重要的试验手段,建议我国新造车体按其实际运行过程中承受的交变气动载荷加载进行疲劳强度试验。

导气与枪管浮动混合式自动机动力学特性研究

为了研究导气与枪管浮动混合式自动机在高初速榴弹发射器上应用的可行性及通过调节导气装置结构参数匹配枪管组件与枪机框组件后坐能量达到降低武器系统后坐力的目的,基于气体动力学理论和热力学理论,推导考虑热量散失及枪管浮动作用的内弹道和导气装置气流问题的基本方程组。利用该计算模型对高初速榴弹发射器发射动力学进行仿真,得出武器系统自动机运动特性曲线及后坐力随时间变化的曲线。将仿真结果与实验结果进行对比,验证模型的正确性。探讨导气装置导气孔直径、导气孔开孔位置、导气室初始容积结构参数对导气室气体压力变化的影响规律,并分析其对自动机速度曲线及后坐力的影响。在完成自动机自动循环的前提下,采用导气与枪管浮动混合式自动机可将武器的最大后坐力控制在1 100 N内,实现武器低后坐发射。

厢式货车减阻研究

为了减少厢式货车在行驶过程中所受到的气动阻力,从而达到节能减排的目的,本文设计适于厢式货车使用的新型空气动力学附加装置并基于商业软件FLUENT中的RNGκ-ε紊流模型进行数值计算。结果表明:该新型空气动力学装置明显地改变了厢式货车周围流场特性;同时分析速度场和货车表面压力场,获得了该新型附加装置的理论减阻率及其减阻机理。

扰流装置对轿车气动特性的影响研究

以简化的轿车模型为研究对象,以计算流体力学软件ANSYS-FLUENT为研究工具对轿车的气动特性进行了研究。计算了加装扰流装置前和加装扰流装置后的车身阻力系数和升力系数。分析了三种造型的扰流装置对轿车气动特性的影响。计算结果表明:扰流装置的加装可以改善轿车尾部流场结构,轿车尾部区域涡流现象和倒流现象均明显减弱;加装不同扰流板均会不同程度地增加轿车的阻力系数,但同时可以减小轿车升力系数,进而一定程度改善汽车的空气动力学特性。

赛车空气动力学套件设计与气动特性研究

FSAE赛车的空气动力学特性对其动力性、燃油经济性、操纵稳定性及制动性有重要影响。文中依据大赛规则设计了FSAE赛车空气动力学套件,基于CFD方法对比分析了3种不同参数的尾翼组合方案的气动特性,确定了最优的尾翼组合方案,根据最优方案的尾翼参数对前翼的参数进行了匹配;研究了有、无空气动力学套件的赛车的空气动力学特性,安装空气动力学套件后,赛车的气动升力系数由0.28下降到-1.19,气动阻力系数由0.44变为0.68,下压力显著增加;基于MATLAB对有、无空气动力学套件的赛车在特征赛道上的性能进行了计算,结果表明:赛车加装空气动力学套件后有效提高了过弯速度,推迟了刹车点,提高了圈速,有效提高了赛车的操纵稳定性和动力性。

气动附加装置降低厢式货车后体阻力

在风洞中通过天平测力和静态压力传感器测压实验,研究了简易厢式货车模型安装背部隔栅气动附加装置后阻力特性和背部压力分布的变化。结果表明采用高度适当、布置合理的背部隔栅,可以使厢式货车后体侧缘的分离剪切层再附于隔板上并在隔板后缘再次分离。从而使厢式货车下游的分离尾涡区变窄,提高其背部压力,最终减小了厢式货车模型因后体分离引起的压差阻力。实验发现减阻效果最好的是采用的3横3竖形式、高度为50mm、距离厢式货车后体边缘30mm的隔栅,最大可以将模型的阻力减小7.19%。

厢式货车尾部打孔装置减阻特性研究

对厢式货车周围流场进行了CFD数值模拟,分析了产生气动阻力的主要原因,在此基础上,设计了一种可以消除尾部漩涡场的新型打孔式空气动力学附加装置,并将装置进一步改进得到其优化模型。基于RNGk-ε紊流模型进行数值计算,分析货车周围速度场及其表面压力场,获得该新型附加装置的理论减阻率及其减阻机理。结果表明该空气动力学装置改善了厢式货车尾部湍流场,在前端加装导流罩的基础上进一步获得了6.04%的减阻率。研究结果为厢式货车的减阻节能研究提供了理论依据和有价值的参考。

气力轮式排种器动压充种机理及试验研究

试验研究发现气力轮式排种器的充种室内存在３种典型气固两相流态：沉降搅渗流态；带动渗流流态；惯性回流流态。全面分析了气力轮式排种器的动压充种机理。

高速磁悬浮列车纵向及垂向气动力数值分析

采用数值分析的方法研究高速磁悬浮列车在纵向风作用下所受气动力和力矩。利用三维粘性定常不可压缩Navier Stokes方程,k～ε两方程紊流模型,采用有限体积法计算高速磁悬浮列车在不同运行速度条件下20个工况点的气动阻力,升力和俯仰力矩;分析了车下空气隙尺寸对上述气动力的影响,并与轮轨型列车的气动力特征作了比较。计算结果表明,车下空气隙的大小对列车运行的空气阻力只有微小的影响,但对气动升力的影响较大;随着车速的提高,气动阻力、升力和俯仰力矩均有较大幅度提高,不同的计算模型其提高幅度是不一样的。

先进翼尖装置流体动力特性数值模拟与分析研究

对民用客机上使用较多的两种翼尖装置(融合式翼梢小翼和翼尖涡扩散器)进行了对比分析与研究。在基本机翼参数相同的基础上,利用ICEM软件对基本机翼及分别加装两种不同翼尖装置的机翼生成点对点对接的高质量多块结构化计算网格,采用Roe三阶迎风偏置通量差分裂方法和隐式近似因子分解法求解耦合SA湍流模型的雷诺平均Navier-Stokes方程。通过计算得知:在巡航状态下分别加装融合式小翼和翼尖涡扩散器后,两种机翼的升阻比分别提高了10.945%和4.993%,俯仰力矩系数分别增加了9.410%和5.116%,翼根弯矩系数分别增加了7.380%和1.013%。分析结果表明:相比于翼尖涡扩散器,融合式翼梢小翼能更显著地提高机翼的升阻比,但同时也较为明显地增加了机翼的俯仰力矩和翼根弯矩,从而导致飞机配平阻力和翼根结构重量的增加。

突风口环境下的高速列车周围流场数值模拟

基于三维、非定常、可压缩雷诺时均N-S方程和标准κ-ε双方程湍流模型,利用滑移网格方法模拟突风口高速列车气动性能,分析得到流场随时间的变化以及车体在各个时刻承受的气动力。研究结果表明:未进入风区时,车体周围流场基本对称分布,迎风侧和背风侧两侧的压力分布没有明显差异;在列车车尾进入风区至列车车头驶出风区这段时间,车体整体处于横风区域内,运行过程中,迎风侧压力和背风侧压力有明显不同;受来流风速的影响,车体迎风侧压力呈现正压分布,车体背风侧压力呈现负压状态,列车车尾驶出横风区域,与列车未整体进入横风区域类似,列车驶出风区后,列车车体周围流场又恢复对称性质。与风洞试验结果对比,数值计算误差在5%以内。