基于相似理论的矿井回风源分离式热管研究

以山西省某实际矿用分离式热管换热系统为原型，基于相似原理，得到几何、风速、换热量等物理量的相似倍数关系，搭建以R22为传热工质的矿井回风源分离式热管换热系统，开展变风量实验。结果显示：努塞尔数Nu实验值与经验值的平均偏差达到40%，欧拉数Eu实验值与经验值的偏差最高达到71.53%。现有的Briggs&Young传热、阻力经验公式不能准确描述矿井回风余热回收背景下的分离式热管换热器传热及阻力损失情况，提出适用于该条件的传热、阻力特性实验关联式，并给出适用范围。     

非饱和土壤内部水-气界面特性的微CT 分析

以不同粒径玻璃微珠为对象,通过高分辨率Micro-CT测量获得非饱和土壤内部水-气界面的分布状态特征,并采用欧拉数(Eu)表征土壤内部孔隙的连通特性。结果表明,Eu随饱和度S变化可分为3个阶段,其中当S25%时,Eu随饱和度线性降低;当25%S35%时,Eu随饱和度缓慢降低,直至减小至零;当S35%时,Eu呈现负值,且变化非常微弱。土壤内部的水-气接触面积随饱和度的增加呈现快速上升而后逐渐下降的整体变化趋势。最后,以热导率为例,量化水-气界面状态变化对不同温度下土壤宏观热物性的影响,并分析土壤内部水-气扩散与流动机制。     

柴油机进气道流热耦合计算研究

通过数值模拟方法对气道进行计算，计算结果与实验结果基本相符，证明了数值计算的可靠度。然后计算得到了气道直道弯道部分的准则方程式，最后分析了离心浮升力对气道内部对流换热的影响。     

弗劳德准则于迷宫式水蓄冷模型实验的适应性研究

为分析迷宫式筏基水蓄冷的蓄冷效率,建立筏基模型进行蓄冷/释冷模拟实验。实验欲利用流体力学相似性原理的重力相似,也即弗劳德准则数。为增加模型实验的说服力,将根据弗劳德准则数确立的实验模型建立CFD(Computational Fluid Dynamics)模拟(即计算流体动力学仿真模拟),并与原型CFD模拟结果对比。通过对比两者实验结果,发现模型与原型结果一致,两者相似,最终说明以弗劳德准则数建立迷宫式水蓄冷模型的实验原理正确,可应用于模型实验。     

流化床锅炉燃烧室的流体动力学模拟

流化床的放大效应十分显著,使得流化床的试验研究在大型工业流化床设计中的应用发生问题。近年来在国外发展起来的流化床模拟放大技术是从流态化现象的基本控制方程出发,根据相似原理导出一组无量纲相似准则数。这些准则数建立了不同条件下(结构尺寸、温度、压力和床料特性等)的流化性能间相似的内在关系,对流化床的试验研究及设计实践有重要的指导意义及应用前景。     

柴油机进气道流热耦合计算研究

通过数值模拟方法对气道进行计算,计算结果与实验结果基本相符,证明了数值计算的可靠度。然后计算得到了气道直道弯道部分的准则方程式,最后分析了离心浮升力对气道内部对流换热的影响。     

横掠螺旋管束流动传热的数值模拟

螺旋管是一种紧凑式换热器的芯体形式,在工程中有较多应用。本文对螺旋管管束的流动传热情况进行了数值模拟研究,无量纲螺距0.15～0.3,进口雷诺数1000～5000,获得了横掠复杂螺旋管束的流场和温度场。结果表明：管外平均努赛尔数随雷诺数的增大而增大,欧拉数随雷诺数的增大而减小;减小螺距使平均努赛尔数和欧拉数均增大,且对欧拉数的影响要明显大于努赛尔数。同时通过对数值结果进行拟合给出了管束换热的关联式,式中考虑了无量纲螺距的影响。     

针型管换热器换热性能与阻力特性试验研究

针型管是一种具有简单结构,易于制造生产的新型换热元件,相比于一些其他的常见换热器,具有更大的换热面积以及更强的换热效果。对一种特殊结构的针型管换热器进行了换热及阻力性能的试验研究,得出了该针型管的平均努塞尔数Nu和欧拉数Eu的计算关联式,并计算得到了该针型管换热器针型管侧的对流换热系数。试验和计算结果为相关的以针型管为换热原件的换热装置的设计提供了参考。     

轴流压气机氦气和空气工质相似问题研究

当氦气轴流压气机的轴向速度≤200 m/s,在保证完全相同的几何尺寸条件下,以高压段第一级为模拟机,其参数为氦气流量4.72 kg/s,进口压力1.0 253×106Pa,入口温度35.5℃.采用空气代替氦气模拟氦气压缩机高压段第一级,研究了氦气和空气两种不同工作介质的物理参数如密度、粘度、绝热指数差异引起的运动和动力不完全相似问题.分别采用确定物理量法和微分方程法对相似准则的确立进行对比分析,比较氦气工质和空气工质的差异性及其对相似准则选择的影响.分析产生偏差的原因,确立用空气模拟氦气压气机的相似准则为Sr、Re、Eu,计算出与氦气压气机设计工况相对应的空气模拟参数,对比分析CFD计算表明,模拟效果良好,该研究为氦气压气机试验提供了理论依据.     

超低NOx燃油燃烧器的燃烧相似性研究

基于相似性原理,分析了影响燃烧相似的流动雾化燃烧过程的相似准则数。对燃烧室原模型和尺缩模型进行数值模拟,对比分析了两模型的流场、温度场、组分场,结果表明:在满足两模型雷诺数均进入第二自模区,保证气液速度比和Da准则数相同的情况下,可以满足尺缩模型与原模型的湍流燃烧过程相似。此外,还进一步探讨了容积热负荷倍数对于燃烧相似性的影响,研究表明:在满足流动相似的条件下,尺缩模型采用较低倍数的容积热负荷时与原模型有更好的相似性。     

A Study of the Impulse Wave Discharged from the Exits of Two Parallel Tubes

The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to understand the detailed flow physics associated with the twin impulse wave, compared with those in a single impulse wave. In the current study, the merging phenomena and propagation characteristics of the impulse waves are investigated using a shock tube experiment and by numerical computations. The Harten-Yee's total variation diminishing (TVD) scheme is used to solve the unsteady two-dimensional compressible Euler equations. The Mach number Ms of incident shock wave is changed below 1.5 and the distance between two-parallel tubes, L/d, is changed from 1.2 to 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. The results obtained show that on the symmetric axis between two-parallel tube     

The Problems of Inaccuracy in Flow Capacity Definition by Using Different Numerical Techniques

The results of numerical analysis of turbine flow capacity and other parameters at different turbine rows are presented in this paper. Mass flow calculations by 3D Euler code has been controlled by means of 3D Navier-Stokes code taking into account inlet turbulence intensity and turbulence scale. The use of complicated numerical approaches (3D Euler or 3D Navier-Stokes codes) for mass flow definition demands close attention to quality of numerical techniques. Various reasons of inaccuracy of mass flow definition by using different 3D numerical approaches are analyzed.     

Research of the gas-solid flow character based on the DEM method

Numerical simulation of gas-solid flow behaviors in a rectangular fluidized bed is carried out three dimensionally by the discrete element method (DEM). Euler method and Lagrange method are employed to deal with the gas phase and solid phase respectively. The collided force among particles, striking force between particle and wall, drag force, gravity, Magnus lift force and Saffman lift force are considered when establishing the mathematic models. Soft-sphere model is used to describe the collision of particles. In addition, the Euler method is also used for modeling the solid phase to compare with the results of DEM. The flow patterns, particle mean velocities, particles’ diffusion and pressure drop of the bed under typical operating conditions are obtained. The results show that the DEM method can describe the detailed information among particles, while the Euler-Euler method cannot capture the micro-scale character. No matter which method is used, the diffusion of particles increases with the increase of gas velocity. But the gathering and crushing of particles cannot be simulated, so the energy loss of particles’ collision cannot be calculated and the diffusion by using the Euler-Euler method is larger. In addition, it is shown by DEM method, with strengthening of the carrying capacity, more and more particles can be schlepped upward and the dense suspension upflow pattern can be formed. However, the results given by the Euler-Euler method are not consistent with the real situation.     

Busemann diffuser for supersonic ramjet engine with detonation combustion of hydrogen-air mixture

The expediency of using a Busemann diffuser in a scramjet engine with detonation combustion of hydrogen-air mixtures is studied. A method is developed for calculating an air intake that provides spontaneous initiation of oblique detonation in a hydrogen-air mixture under conditions of rarefied atmosphere at hypersonic freestream Mach numbers. The geometry of the Laval nozzle (convergent-expanding) with the Busemann diffuser for the free flow Mach number 9 is determined. It is shown that at an altitude of about 40 km, the detonation combustion of the hydrogen-air mixture in this nozzle can provide more than 0.4 tons of thrust and more than 35% efficiency. The mathematical model is based on unsteady two-dimensional Euler equations for axisymmetric multicomponent reacting gas flow. To simulate chemical transformations, the detailed kinetic scheme is used that takes into account 33 non-equilibrium reactions for nine components of the mixture. The heat capacity, enthalpy, and entropy of a mixture are calculated using the reduced Gibbs energy of the gas components. Numerical modeling is carried out according to the modified Godunov scheme of the second order of approximation in spatial variables.     

冲击式水轮机含沙三相流与磨损特性数值研究

冲击式水轮机在高水头水力资源开发中具有重要的应用前景,但其过流部件的泥沙磨损问题会是重要挑战.冲击式机组内部流动过程复杂,流动状态的转换多;挟沙流动时,水气沙三相流动特性尚不明确,目前相关研究仍然较为匮乏.本文采用欧拉—拉格朗日方法对颗粒在冲击式水轮机内的全流动过程进行了数值模拟,详细地分析了三相流的水力特性、泥沙颗粒...     

Predictions of turbulent flow and heat transfer in gas–droplets flow downstream of a sudden pipe expansion

Droplets-laden turbulent flow downstream of a sudden pipe expansion has been investigated by using Euler/Euler two-fluid model for the gaseous and dispersed phases. Significant increase of heat transfer in separated flow at the adding of evaporating droplets has been demonstrated (more than 2 times compare with one-phase flow at the value of mass concentration of droplets M_L1  0.05). Addition of dispersed phase to the turbulent gas flow results in insignificant increase of the reattachment length. Low-inertia droplets (d₁  50 μm) are well entrained into the circulation flow and present over the whole pipe section. Large particles (d₁ ≈ 100 μm) go through the shear layer not getting into the detached area. Comparison with experimental data on separated gas–droplets flows behind the plane backward-facing step has been carried out.     

球床沸水堆燃料组件稳态换热数值模拟研究

以球床沸水堆（PBWR）燃料组件为研究对象,运用CFD商用软件FLUENT,采用多孔介质模型和欧拉两相流模型,燃料组件流动沸腾换热进行计算分析。分析额定工况下的燃料组件内稳态热工水力特性及孔隙率对计算结果的影响。计算结果表明：球床沸水堆燃料组件横截面的热工参数分布与传统压水堆的壁面加热管道相比具有新的特点,采取适当的燃料组件结构孔隙率,可获得较大堆芯换热效率及较小的堆芯压降。     

The initiation and propagation of detonation in supersonic combustible flow with boundary layer

Adaptive simulations solving the Navier-Stokes equations have been conducted in order to get a better understanding on the detonation initiation and propagation in a stoichiometric H₂/O₂/Ar supersonic mixture with boundary layer. The detonation is initiated by a continuous hot jet. When reflecting on the wall, the jet induced bow shock interacts with the boundary layer and forms the shock boundary layer interaction phenomena, while in Euler result the bow shock forms Mach reflection. The investigation shows that the Navier-Stokes simulation result is structurally in better agreement with the experiment compared with that of the inviscid Euler simulation result. The bow shock interacts with the separation shock, forming the shock induced combustion behind the interaction zone. Then the combustion front couples with shock and forms Mach stem induced detonation. The Mach stem induced detonation continues to getting higher and propagating upstream, initiating the main flow. The initiated partial detonation exists with the separation shock induced combustion front, forming an “oblique shock induced combustion-partial detonation” structure in the main flow. The investigation on the influence of free stream Mach number further confirms that the boundary layer has an important influence on detonation initiation. The parametric studies also show that there exists a free stream Mach number range to initiate the partial detonation in supersonic combustible flow successfully.     

Numerical Modelling of the Aeroelastic Behaviour and Variable Loads for the Turbine Stage in 3D Transonic Flow

Introduction Aeroelastic phenomena in the turbine stage are characterized by instability, continuous interaction and energy exchange between the fluid and the structure; so they cannot be studied properly in the frame of each of uncoupled domains separately (aerodynamics or structural dynamics). The traditional approach in flutter calculations of bladed disks is based on frequency domain analysis[1,2], in which the blade motion is assumed to be a harmonic function of time with a constant phas…