基于CFD的具有首翼的新型飞翔形式AUV升力和阻力估计:对阻力极曲线和推力估计的见解

To achieve hydrodynamic design excellence in Autonomous Underwater Vehicles(AUVs)largely depends on the accurate prediction of lift and drag forces.The study presents Computational Fluid Dynamics(CFD)-based lift and drag estimations of a novel torpedo-shaped flight-style AUV with bow-wings.The horizontal bow-wings are provided to accommodate the electromagnetic arrays used to perform the cable detection and tracking operations near the seabed.The hydrodynamic performance of the AUV due to addition of these horizontal bow-wings is required to be investigated,particularly at the initial design stage.Hence,CFD techniques are employed to compute the lift and drag forces observed by the flight-style AUV,maneuvering underwater at different angles of attack and varying speeds.The Reynolds-Averaged Navier-Stokes Equations(RANSE)closure is achieved by employing the modified k-ϵ model and Two-Scale Wall Function(2-SWF)approach is used for boundary layer treatment.Further,the study also highlights the unique mesh refinement and solution-adaptive meshing techniques to perform the CFD simulations in Solidworks Flow Simulation(SWFS)environment.The drag polar curve for flight-style AUV with and without bow-wings is generated using the computed lift and drag coefficients.The curve provided essential insights for achieving hydrodynamically efficient and optimized AUV design.From the drag polar curve,it is revealed that due to horizontal bow-wings,the flight-style AUV is capable to generate higher lift with less drag and thus,it gives better lift-to-drag ratio compared to the AUV without bow-wings.Moreover,simulated results of axial drag observed by the AUV have also been compared with free-running experimental results and are found in good agreement.

水流与海浪对HATST功率性能的CFD模拟

为确保涡轮机的长期可靠性,在设计潮流涡轮机时应考虑海浪条件。使用直径为0.9 m的三叶片水平轴潮流涡轮机(Horizontal Axis Tidal Stream Turbine,HATST)作为基准模型,采用计算流体动力学(Computational Fluid Dynamics,CFD)开源软件OpenFOAM预测HATST在海浪和水流条件下的性能。对其进行网格依赖性测试以选择最佳网格数,捕捉流动特征。将生成的波浪轮廓与三阶Stokes波浪理论结果进行比较,发现模拟结果与理论结果一致。研究不同波频和波幅对HATST功率性能的影响,结果表明,波幅对功率性能的影响较为明显,波频的影响相对较小。

空气润滑系统通风设计与CFD数值模拟

为增强通风系统设计的针对性和可靠性,提出一种满足空气润滑系统(AirLubrication System,ALS)压缩机正常运行的通风设计方案,并采用ANSYSFLUENT软件对温度场和压力场的分布情况进行分析,对通风设计的可靠性和合理性进行验证。研究成果可为空气润滑系统的通风设计提供一定参考。

COMPUTATIONAL FLUID DYNAMICS(CFD) SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

Computational fluid dynamics（CFD） simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 pm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.

A Computational Fluid Dynamics (CFD) Analysis of an Undulatory Mechanical Fin Driven by Shape Memory Alloy

Many fishes use undulatory fin to propel themselves in the underwater environment. These locomotor mechanisms have a popular interest to many researchers. In the present study, we perform a three-dimensional unsteady computation of an undulatory mechanical fin that is driven by Shape Memory Alloy （SMA）. The objective of the computation is to investigate the fluid dynamics of force production associated with the undulatory mechanical fin. An unstructured, grid-based, unsteady Navier-Stokes solver with automatic adaptive remeshing is used to compute the unsteady flow around the fin through five complete cycles. The pressure distribution on fin surface is computed and integrated to provide fin forces which are decomposed into lift and thrust. The velocity field is also computed throughout the swimming cycle. Finally, a comparison is conducted to reveal the dynamics of force generation according to the kinematic parameters of the undulatory fin （amplitude, frequency and wavelength）.

结合CFD技术的跨音速动导数计算方法研究

在非结构化动态网格技术基础上,采用二阶精度的中心有限体积法和全隐式双时间推进方法进行非定常欧拉方程求解。通过建立动导数计算模型,发展结合CFD的飞行器跨音速动导数计算方法。通过三维跨音速非定常欧拉方程的求解,数值模拟了国外动导数计算标模Finner导弹的跨音速非定常绕流问题,进而计算了Finner导弹的跨音速纵向组合动导数,计算结果和文献中的风洞实验结果吻合较好,体现了方法的正确性。

基于CFD的船用柴油机缸体水套设计

利用数值模拟对6170型船用柴油机的冷却水套进行了冷却性能研究,优化设计了缸体冷却水套。对原机缸体冷却水套内冷却水的流场分布、冷却水套内壁面换热系数、各缸冷却均匀性和压力损失进行了分析。计算结果表明:原机缸体水套上部存在冷却强度不足、冷却均匀性差的缺陷,不能满足缸套冷却要求。通过计算提出了提高缸体上部冷却强度及改善冷却均匀性的优化设计方案,从而满足了气缸套的冷却需要,确保了发动机工作的可靠性。

侧风下磁浮列车-箱梁组合系统气动特性

与轮轨列车-桥梁组合系统不同,常导磁浮列车-桥梁系统采用“车抱轨”的结构形式,且列车底部与桥梁之间的空气通道极其狭窄,使得侧风下磁浮列车-桥梁组合系统的空气流动、气动力出现新的特征。本文以常导抱轨式高速磁浮列车和简支箱梁桥为研究对象,建立侧风数值分析模型,探讨组合系统的雷诺数效应,确定合适的模拟风速。在此基础上,对侧风下磁浮列车-箱梁组合系统的侧风气动特性进行分析,为磁浮交通的抗风运营安全提供参考。结果表明:磁浮列车-箱梁组合系统的气动特性与雷诺数密切相关,列车、箱梁气动性能受组合影响变化较大,线间距对系统气动性能的影响不明显,增大梁高会使系统气动力略有增加。

CFD-supported optimization of flow distribution in quench tank for heat treatment of A357 alloy large complicated components

The flow distribution in quench tank for heat treatment of A357 alloy large complicated components was simulated using FLUENT computational fluid dynamics（CFD） software.The flow velocity and the uniformity of flow field in two types of quench tanks（with or without agitation system） were calculated.The results show that the flow field in the quench tank without agitation system has not evident regularity.While as for the quench tank with agitation system,the flow fields in different parameters have certain regularity.The agitation tanks have a distinct advantage over the system without agitation.Proper process parameters were also obtained.Finally,the tank model established in this work was testified by an example from publication.This model with high accuracy is able to optimize the tank structures and can be helpful for industrial production and theoretical investigation in the fields of heat treatment of large complicated components.

垂直轴风机功率增强的翼型与阵列优化

针对H型垂直轴风机(Vertical Axis Wind Turbine,VAWT),通过计算流体动力学(Computational Fluid Dynamics,CFD)模拟,将翼型设计与涡轮阵列相关联,对比分析多种翼型及不同阵列条件下VAWT的转矩系数C_(m)、功率系数C_(P)和平均功率参数Ω。结果表明:与对称翼型相比,非对称翼型在高叶尖速比下功率系数较小,弯度效应可显著增大翼型在下风区的功率系数;在风场阵列中,三涡轮阵列优化后下风区涡轮功率显著提升,单涡轮功率可提升40%,风场整体功率提升约20%;针对海上牧场结构平面提出五涡轮阵列,优化后风场整体效率提升65%,单涡轮性能提升可达100%。研究成果对于提高深远海网箱系统功能与设计具有推动意义。

Investigation of the Interaction Between the Free Surface and A Semi/Shallowly Submerged Underwater Vehicle

The present study aims to investigate the interaction between the free surface and a semi/shallowly submerged underwater vehicle,especially when the submergence depth h is smaller than 0.75D(D:submarine maximum diameter).In this respect,the straight-ahead simulations of the generic SUBOFF underwater vehicle geometry are conducted with constant forward velocities using the Unsteady Reynolds-Averaged Navier-Stokes(URANS)equations with a Shear-Stress Transport(SST)k-ωturbulence model in commercial code Fluent,at submergence depths and Froude numbers ranging from h=0 to h=3.3D and from Fn=0.205 to Fn=0.512,respectively.The numerical models are verified against the existing experimental data.The analysis of the obtained results indicates that in the case of the semi and shallowly submerged underwater vehicle(UV),both the submergence depth and forward velocity have a great effect on the behaviors of hydrodynamic forces acting on the UV.The magnitude of maximum total resistance may reach almost five times the value of resistance exerted on the totally submerged hull.Both the forces acting on the UV and the generated waves when the submergence depth h is smaller than 0.75D are significantly different from those whenr h is larger than 0.75D.The conclusions can be used as reference for future research on near free surface motions of underwater vehicles and the design of small water-plane area twin hull.

Influence of the Ambient Temperature on the Efficiency of Gas Turbines

In hot and arid regions like the Saharan area,effective methods for cooling and humidifying intake air are essential.This study explores the utilization of a water trickle cooler as a promising solution to meet this objective.In particular,the HASSI MESSAOUD area is considered as a testbed.The water trickle cooler is chosen for its adaptability to arid conditions.Modeling results demonstrate its effectiveness in conditioning air before it enters the compressor.The cooling system achieves a significant temperature reduction of 6 to 8 degrees Celsius,enhancing mass flow rate dynamics by 3 percent compared to standard cases without cooling.Moreover,the cooling system contributes to a remarkable 10 percent reduction in power consumption of gas turbines and a notable 10 percent increase in turbine efficiency.These findings highlight the potential of water trickle coolers in improving the performance and efficiency of gas turbine systems in hot and dry climates.

Experimental and Numerical Investigation on the Aerodynamic Characteristics of High-Speed Pantographs with Supporting Beam Wind Deflectors

Aiming to mitigate the aerodynamic lift force imbalance between pantograph strips,which exacerbates wear and affects the current collection performance of the pantograph-catenary system,a study has been conducted to support the beam deflector optimization using a combination of experimental measurements and computational fluid dynamics(CFD)simulations.The results demonstrate that the size,position,and installation orientation of the wind deflectors significantly influence the amount of force compensation.They also indicate that the front strip deflectors should be installed downwards and the rear strip deflectors upwards,thereby forming a“π”shape.Moreover,the lift force compensation provided by the wind deflectors increases with the size of the deflector.Alternative wind compensation strategies,such as control circuits,are also discussed,putting emphasis on the pros and cons of various pantograph types and wind compensation approaches.

The Analysis of Human Behaviour and Evacuation in a Fire Situation in a Building for Higher Education

The paper presents the analysis of a human evacuation from a higher education building located in Iassy,Romania,by means of engineering techniques to approach fire safety.Because in Romania(as in other European countries)fire safety design of buildings is prescriptive and not performance-based,a fire safety engineering approach arouse great interest in many countries such as the U.S.A.,Australia,New Zealand,England,Sweden,Finland,etc.This paper is based on the assumption of starting a fire in the space of a hall for festivities,located on the ground floor of the building,near two human evacuation routes;We consider two building evacuation scenarios:two exits and,respectively,just one exit(assuming that the second would be accidentally blocked).

Numerical Study on the Aerodynamic and Fluid−Structure Interaction of An NREL-5MW Wind Turbine

A 5-MW wind turbine has been modeled and analyzed for fluid-structure interaction and aerodynamic performance.In this study, a full-scale model of a 5-MW wind turbine is first developed based on a computational fluid dynamics(CFD) approach, in which the unsteady, noncompressible Reynolds Averaged Navier-Stokes(RANS) method is used. The main focus of the study is to analyze the tower shadow effect on the aerodynamic performance of the wind turbine under different inlet flow conditions. Subsequently, the finite element model is established by considering fluid/structure interactions to study the structural stress, displacement, strain distributions and flow field information of the structure under the uniform wind speed. Finally, the fluid-structure interaction model is established by considering turbulent wind and the tower shadow effect. The variation rules of the dynamic response of the one-way and two-way fluid-structure interaction(FSI) models under different wind speeds are analyzed, and the numerical calculation results are compared with those of the centralized mass model. The results show that the tower shadow effect and structural deformation are the main factors affecting the aerodynamic load fluctuation of the wind turbine, which in turn affects the aerodynamic performance and structural stability of the blades. The structural dynamic response of the coupled model shows significant similarity, while the structural displacement response of the former exhibits less fluctuation compared with the conventional centralized mass model. The one-way fluid-structure interaction(FSI)model shows a higher frequency of stress-strain and displacement oscillations on the blade compared with the two-way FSI model.

基于CFD方法的球床式高温气冷堆稳态热工水力分析

基于CFD通用计算程序Fluent,开发了多孔介质流固两相局域非热平衡模型,对PBMR-400满功率名义工况下稳态热工水力行为进行了分析。高温气冷堆堆芯的热工水力计算模型通常为带有强内热源宏观的多孔介质模型,Fluent程序本身的多孔介质模型为局域热平衡模型,无法恰当描述堆芯热工水力行为。通过开启Fluent的自定义标量场(UDS)功能并在动量方程上附加阻力源项,实现了局域非热平衡模型,能够精确地计算球床堆堆芯热工水力行为。CFD程序使用了非常精细的网格,可以计算更加精细的流场和温场分布。计算表明,Fluent的结果与国际上著名的球床堆热工水力程序THERMIX,TINTE符合较好,可以作为球床堆热工水力分析工具。

Detection of Partial and Extended Blockages: A Case Study of Edible Oil Pipeline System

This work focuses on the development and implementation of a simulation-based approach for the detection of partial and extended blockages within an edible oil pipeline system. Blockages, whether partial or extended, pose a significant operational and safety risks. This study employs computational fluid dynamics (CFD) simulations to model the flow behaviour of edible oil through pipeline under varying conditions. It leverages advanced computational fluid dynamics (CFD) simulations to analyze pressure, velocity, and temperature variations along the pipeline. By simulating scenarios with different blockage characteristics, there is establishment of distinctive patterns indicative of partial and extended obstructions. Through extensive analysis of simulation data, sensing element, and monitoring system, processing signal input and response output, the system can accurately pinpoint the location and severity of blockages, providing crucial insights for timely intervention. The detection system represents a significant advancement in pipeline monitoring technology, offering a proactive and accurate approach to identify blockages and mitigate potential risks and ensure the uninterrupted flow of edible oil, thereby enabling timely intervention and maintenance.

Investigating the Effects of Injection Pipe Orientation on Mixing and Heat Transfer for Fluid Flow Downstream a T-Junction

At T-junctions, where hot and cold streams flowing in pipes join and mix, significant temperature fluctuations can be created in very close neighborhood of the pipe walls. The wall temperature fluctuations cause cyclical thermal stresses which may induce fatigue cracking. Temperature fluctuation is of crucial importance in many engineering applications and especially in nuclear power plants. This is because the phenomenon leads to thermal fatigue and might subsequently result in failure of structural material. Therefore, the effects of temperature fluctuation in piping structure at mixing junctions in nuclear power systems cannot be neglected. In nuclear power plant, piping structure is exposed to unavoidable temperature differences in a bid to maintain plant operational capacity. Tightly coupled to temperature fluctuation is flow turbulence, which has attracted extensive attention and has been investigated worldwide since several decades. The focus of this study is to investigate the effects of injection pipe orientation on flow mixing and temperature fluctuation for fluid flow downstream a T-junction. Computational fluid dynamics (CFD) approach was applied using STAR CCM+ code. Four inclination angles including 0 (90), 15, 30 and 45 degrees were studied and the mixing intensity and effective mixing zone were investigated. K-omega SST turbulence model was adopted for the simulations. Results of the analysis suggest that, effective mixing of cold and hot fluid which leads to reduced and uniform temperature field at the pipe wall boundary, is achieved at 0 (90) degree inclination of the branch pipe and hence may lower thermal stress levels in the structural material of the pipe. Turbulence mixing, pressure drop and velocity distribution were also found to be more appreciable at 0 (90) degree inclination angle of the branch pipe relative to the other orientations studied.

Comprehensive Examination of Solar Panel Design: A Focus on Thermal Dynamics

In the 21st century, the deployment of ground-based Solar Photovoltaic (PV) Modules has seen exponential growth, driven by increasing demands for green, clean, and renewable energy sources. However, their usage is constrained by certain limitations. Notably, the efficiency of solar PV modules on the ground peaks at a maximum of 25%, and there are concerns regarding their long-term reliability, with an expected lifespan of approximately 25 years without failures. This study focuses on analyzing the thermal efficiency of PV Modules. We have investigated the temperature profile of PV Modules under varying environmental conditions, such as air velocity and ambient temperature, utilizing Computational Fluid Dynamics (CFD). This analysis is crucial as the efficiency of PV Modules is significantly impacted by changes in the temperature differential relative to the environment. Furthermore, the study highlights the effect of airflow over solar panels on their temperature. It is found that a decrease in the temperature of the PV Module increases Open Circuit Voltage, underlining the importance of thermal management in optimizing solar panel performance.

CFD simulation of ammonia-based CO_2 absorption in a spray column

A comprehensive computational fluid dynamics（CFD） model is developed based on the gas-liquid two-phase hydrodynamics,gas-liquid mass-transfer theory and chemical reaction kinetics,and the ammonia-based CO2 absorption in a spray column is numerically studied.The Euler-Lagrange model is applied to describe the behavior of gas-liquid twophase flowand heat transfer.The dual-film theory and related correlations are adopted to model the gas-liquid mass transfer and chemical absorption process.The volatilization model of multi-component droplet is utilized to account for ammonia slippage.The effect of operation parameters on CO2 removal efficiency is numerically studied.The results showa good agreement with the previous experimental data,proving the validity of the proposed model.The profile studies of gasphase velocity and CO2 concentration suggest that the flowfield has a significant impact on the CO2 concentration field.Also,the local CO2 absorption rate is influenced by both local turbulence and the local liquid-gas ratio.Furthermore,the velocity field of gas phase is optimized by the method of adjusting the orifice plate,and the results showthat the CO2 removal efficiency is improved by approximately 4%.