蒸汽喷射器的CFD模拟研究

为研究蒸汽喷射器内部复杂的流动现象及工况参数对其性能的影响,基于CFD软件FLUENT对蒸汽喷射器内部流场模拟研究,分析研究了其内部的速度场、压力场及温度场。通过改变工况参数,研究了其对性能的影响。结果表明,存在临界压力使蒸汽喷射器的工作性能最佳。

CFD-DEM simulation of three-dimensional aeolian sand movement

A three-dimensional CFD-DEM model is proposed to investigate the aeolian sand movement.The results show that the mean particle horizontal velocity can be expressed by a power function of heights.The probability distribution of the impact and lift-off velocities of particles can be described by a log-normal function,and that of the impact and lift-off angles can be expressed by an exponential function.The probability distribution of particle horizontal velocity at different heights can be described as a lognormal function,while the probability distribution of longitudinal and vertical velocity can be described as a normal function.The comparison with previous two-dimensional calculations shows that the variations of mean particle horizontal velocity along the heights in two-dimensional and three-dimensional models are similar.However,the mean particle density of the two-dimensional model is larger than that in reality,which will result in the overestimation of sand transportation rate in the two-dimensional calculation.The study also shows that the predicted probability distributions of particle velocities are in good agreement with the experimental results.

Energy management of hybrid electric propulsion system: Recent progress and a flying car perspective under three-dimensional transportation networks

The hybrid electric propulsion system(HEPS)holds clear potential to support the goal of sustainability in the automobile and aviation industry.As an important part of the three-dimensional transportation network,vehicles and aircraft using HEPSs have the advantages of high fuel economy,low emission,and low noise.To fulfill these advantages,the design of their energy management strategies(EMSs)is essential.This paper presents an in-depth review of EMSs for hybrid electric vehicles(HEVs)and hybrid electric aircraft.First,in view of the main challenges of current EMSs of HEVs,the referenced research is reviewed according to the solutions facing real-time implementation problems,variable driving conditions adaptability problems,and multi-objective optimization problems,respectively.Second,the existing research on the EMSs for hybrid electric aircraft is summarized according to the hybrid electric propulsion architectures.In addition,with the advance in propulsion technology and mechanical manufacturing in recent years,flying cars have gradually become a reality,further enriching the composition of the three-dimensional transportation network.And EMSs also play an essential role in the efficient operation of flying cars driven by HEPSs.Therefore,in the last part of this paper,the development status of flying cars and their future prospects are elaborated.By comprehensively summarizing the EMSs of HEPS for vehicles and aircraft,this review aims to provide guidance for the research on the EMSs for flying cars driven by HEPS and serve as the basis for knowledge transfer of relevant researchers.

PDC钻头水力结构优化设计准则及方法探讨

影响钻头性能的因素主要有切削齿结构设计、切削齿技术,水力因素是对钻头性能有显著影响的因素。文章利用计算流体动力学(CFD)技术,通过分析PDC钻头各流道的流量分配、井底速度与压力分布、各刀翼近剖面的漩涡等情况,使钻头水力部分的设计更为合理,从而改善钻头性能。到目前,还没有一个合适的评价PDC钻头水力结构和井底流场优劣的标准,文中根据地层岩石可钻性与岩屑生成机理的不同,分别针对软硬地层,就钻头水力结构优化设计准则给出了一个初步定性的评判标准,为今后PDC钻头水力结构优化提供一定的依据。

迷宫密封三维流场动力学特性计算及研究

迷宫密封气动特性对转子动力学特性的作用明显。应用计算流体动力学技术建立迷宫密封模型,利用计算流体动力学软件Fluent中旋转流场计算方法,对迷宫密封流场进行数值计算,该方法可以将非稳定流场计算转变成稳定流场,从而降低密封流场的计算量。讨论流场参数对其动力学特性的影响。通过对流场计算结果分析发现,气流流速在跨音速时,迷宫密封气动力系数和泄漏量都有较大的变化。因此在工程设计和操作时,要考虑密封中气流流速对转子动力学特性的影响。

Transonic Rudder Buzz on Tailless Flying Wing UAV

Transonic rudder buzz responses based on the computational fluid dynamics or computational structural dynamics(CFD/CSD)loosely method are analyzed for a tailless flying wing unmanned aerial vehicle(UAV).The Reynolds-averaged Navier-Stokes(RANS)equations and finite element methods based on the detailed aerodynamic and structural model are established,in which the aerodynamic dynamic meshes adopt the unstructured dynamic meshes based on the combination of spring-based smoothing and local remeshing methods,and the lower-upper symmetric-Gauss-Seidel(LU-SGS)iteration and Harten-Lax-van Leer-Einfeldt-Wada(HLLEW)space discrete methods based on the shear stress transport(SST)turbulence model are used to calculate the aerodynamic force.The constraints of the rudder motions are fixed at the end of structural model of the flying wing UAV,and the structural geometric nonlinearities are also considered in the flying wing UAV with a high aspect ratio.The interfaces between structural and aerodynamic models are built with an exact match surface where load transferring is performed based on 3Dinterpolation.The flying wing UAV transonic buzz responses based on the aerodynamic structural coupling method are studied,and the rudder buzz responses and aileron,elevator and flap vibration responses caused by rudder motion are also investigated.The effects of attack,height,rotating angular frequency and Mach number under transonic conditions on the flying wing UAV rudder buzz responses are discussed.The results can be regarded as a reference for the flying wing UAV engineering vibration analysis.

发动机氧泵后流场数值仿真研究

发动机氧泵至燃气发生器段的流场结构直接影响着发动机的工作性能,从理论上分析氧泵后是否需要设置整流栅以调整流场,对发动机总体设计十分必要。针对氧泵后流场的特点,借助CFD计算手段,对该段流场进行有整流栅和无整流栅两种情况的数值模拟,计算得到流阻、发生器入口处的总压均匀度、氧阀流量均匀度以及阀芯受力情况。结果表明:氧阀后设置整流栅是有必要的。

Research on Spray, Combustion and Emission Characteristics for DI Diesel Engine

To improve the combustion chamber shape that can decrease the directed injection （DI） diesel emission, the theories of DI diesel spray, combustion and pollutant formation model are analysed and implemented based on the CFD code FIRE. Results show that the chamber with contracting orifice can get stronger squish swirl intensity. The results of the verification studies show a good accordance with the measurements and reveal that the individual processes of spray, evolution, combustion and pollutant formation are well captured in FIRE. Finally, based on the analyzing and comparing of the calculation results of different chambers, a combustion chamber of contracting orifice geometry with lower emission is proposed.

外循环式双层幕墙节能性研究

应用CFD软件对上海市某外循环式双层幕墙热通道进行分析研究,考察热通道内空气的流场及温度分布。采用控制变量法,通过改变双层幕墙开口的位置以及幕墙间距这两个参数,分别计算分析开口位置和幕墙间距对幕墙整体节能性的影响,研究成果可用于指导实际工程中双层幕墙的设计计算。

Efficient three-dimensional high-resolution simulations of flow fields around cylinders

Few works use the fully three-dimensional computational fluid dynamic method to simulate the flow fields around the marine pipes with large aspect ratios due to the huge computation cost.In the present work,an operator-splitting method is used to efficiently solve the three-dimensional Reynolds Average Navier-Stokes governing equations of the fluid flow around pipes by separating the problem as a combination of a two-dimensional problem in the horizontal plane and an one-dimensional problem in the vertical direction.A second order total variation diminishing finite volume method is used to solve the model.The precision of the present model is validated by comparing the present numerical results of two typical three-dimensional cases with the available experimental and numerical results.The simulation results with a commercial software are also included in the comparison and the present model shows a higher performance in terms of computational time.

Simulation on the dynamic stability derivatives of battle-structure-damaged aircrafts

Accurately evaluating the aerodynamic performance of a battle-structure-damaged aircraft is essential to enable the pilot to optimize the flight control strategy. Based on CFD and rigid dynamic mesh techniques,a numerical method is developed to calculate the longitudinal and longitudinal-lateral coupling forces and moments with small amplitude sinusoidal pitch oscillation, and the corresponding dynamic derivatives of two fragment-structure-damaged and two continuous-rod-damaged models modified from the SACCON UAV. The results indicate that, at the reference point set in this paper, additional positive damping is generated in fragment-damaged configurations;thus, the absolute values of the negative pitch dynamic derivative increase. The missing wingtip induces negative pitch damping on the aircraft and decreases the value of the pitch dynamic derivative. The missing middle wing causes a noticeable increase in the absolute value of the pitch dynamic derivative;the missing parts on the right wing cause the aircraft to roll to the right side in the dynamic process, and the pitch-roll coupling cross dynamic derivatives are positive. Moreover, the values of these derivatives increase as the damaged area on the right wing increases, and an optimal case with the smallest cross dynamic derivative can be found to help improve the survivability of damaged aircraft.

汽轮机组迷宫密封泄漏量及气动特性三维CFD数值模拟研究

应用CFD技术建立了梳齿型迷宫密封三维模型,并利用Fluent软件中旋转坐标系计算流场的方法对梳齿型迷宫密封流场进行了数值计算,此方法可以将非稳定流场计算转变成稳定流场,从而降低密封流场的计算量且提高了计算效果。对三维流场计算结果分析发现,密封中气流轴向流速在跨音速时,迷宫密封泄漏量动力学特性发生变化,并进一步修正了密封泄漏量经验计算公式。

Aerodynamics of Ascending Flight in Fruit Flies

As a very basic flight mode, ascending flight is obviously of great importance to all kinds of manmade and natural fliers. Yet, for the most commonly seen fliers - insects, researches on this flight mode are rare. In this paper, we combined both experimental measurements and numerical simulations to investigate the kinematical characteristics, aerodynamic performance and power requirement of ascending flight in fruit flies （Drosophila virilis）. The flies ascend at an advance ratio of about 0.12. The most significant characteristic of ascending flight is larger stroke amplitude compared to hovering, while the other kinematics is very similar. From an aerodynamics point of view, this increased stroke amplitude is needed to overcome the negative effects of＂downwash flow＂, caused by the upward motion of the fly. Same as hovering, the ascending fruit flies utilize delayed stall and fast pitching-up mechanisms to generate the majority of the lift required for balancing the weight and body drag. By using a larger stroke-amplitude to overcome the negative effects of＂downwash flow＂, larger energy cost （about 20%） than that of equivalent hovering is required.

锥形降落伞开伞过程流动结构相互作用的数值模拟

根据多结点开伞模型建立了锥形降落伞系统的变形动力学方程组来对充气过程中的伞衣柔性体变形过程进行模拟.结合多结点模型动力学方程结算代码和计算流体力学软件,对降落伞的充气过程进行流固耦合动态仿真,从而得到充气过程中伞衣外形和流场的变化,以及充气时间、下降速度变化和下降距离等相关数据,与国外研究成果相吻合.

A Rapid and Automatic Optimal Design Method for Six-Stage Axial-Flow Industry Compressor

Existing aerodynamic design systems for multi-stage axial-flow compressor suffer from several limitations,such as experience dependent models and time costly simulations.Few attempts,however,have been devoted to the rapid and automatic optimization of aerodynamic performance at the preliminary design phase,which plays a crucial role in the final aerodynamic performance.In this work,a rapid and automatic aerodynamic optimal design method is developed for the multi-stage axial-flow compressor based on one-dimensional meanline design method,radial-equilibrium equation and genetic algorithm.The one-dimensional performance prediction model includes some popular empirical correlations to calculate the flow loss,incidence angle,deviation angle and flow blockage.The radial-equilibrium equation is solved to obtain the spanwise distribution of aerodynamic and thermodynamic parameters at the inlet and outlet of each blade row.The genetic algorithm is used for an automatic search of the global optimal compressor configuration aiming at maximizing the design efficiency.The developed method is illustrated with the aerodynamic optimal design of a 6-stage axial-flow industry compressor and verified by computational fluid dynamics simulations.The results show that the developed method is capable of improving effectively the design efficiency and predicting accurately the aerodynamic performance of the 6-stage axial-flow industry compressor in a few minutes.This work is of scientific significance to improve the axial-flow compressor design system and of engineering importance to release the designers from the heavy experience dependence especially at the preliminary design phase.

Investigation on One-Dimensional Loss Models for Predicting Performance of Multistage Centrifugal Compressors in Supercritical CO Brayton Cycle

The main compressor in a supercritical carbon dioxide(SCO2)Brayton cycle works near the critical point where the physical properties of CO_(2)are far away from the ideal gas.To investigate the effectiveness of the conventional one-dimensional(1D)loss models for predicting the performance of compressors working in such nontraditional conditions,detailed comparisons of 1D predicted performance,experimental data and threedimensional CFD results are made.A 1D analysis method with enthalpy and total pressure based loss system is developed for multistage SCO2 centrifugal compressors,and it is firstly validated against the experimental results of a single stage SCO2 centrifugal compressor from the Sandia National Laboratory.A good agreement of pressure ratios with experiments can be achieved by the 1D method.But the efficiency deviations reveal the potential deficiencies of the parasitic loss models.On the basis of the validation,a two-stage SCO2 centrifugal compressor is employed to do the evaluation.Three-dimensional CFD simulations are performed.Detailed comparisons are made between the CFD and the 1D results at different stations located in the compressor.The features of the deviations are analyzed in detail,as well as the reasons that might cause these deviations.