Investigation of Particle Deposition Characteristics in Vicinity of Laidback Fan-shaped Film Cooling Holes

To design efficient film cooling systems and mitigate particulate deposition, it is very important to know the influences of the design parameters of film cooling holes on particulate deposition. However, most previous research focused on round film cooling holes. Particle deposition characteristics near shaped film cooling holes need to be studied further. In the present study, numerical computations were carried out to simulate the particle deposition behavior on gas turbine disk samples with laidback fan-shaped film cooling holes by using CFD-DPM (Computational fluid dynamics-discrete particle method). The critical velocities for particle sticking and detachment were determined by EI-Batsh model. Compared with round holes, shaped holes mitigate the particle-wall collision for small particles (d_p≤2μm, ρ_p=990kg/m ³), but promote particle-wall collision for large particles (d_p≥4μm, ρ_p=990kg/m ³). Adding the lateral and forward expansion angle can both cause the decrease of particle deposition efficiency, however, the effect of lateral expansion angle on particle deposition is more active.     

Three-Dimensional Calculations of the Flow Field around a Turbine Blade with Film Cooling Injection near the Leading Edge

Injection of coolant air from a showerhead injection system at the leading edge of a high pressure turbine blade is investigated using a fully implicit three-dimensional finite-volume method on multi-block grids. For various blowing rates, the calculation results for the velocity and pressure fields and turbulence intensity are compared with available experimental data. The present method yields excellent agreement with the experiments for the isentropic Mach number distributions on the blade surface. The standardk–ε turbulence model with wall functions is already capable of capturing the major details of the flow field including the injection-induced secondary-flow vortices, particularly so on the suction side. On the pressure side, however, the lateral jet spreading is under-predicted somewhat together with an exaggeration of the near-wall sink-flow vortices. On this side with convex walls, where turbulence anisotropy is appreciable according to the experiments, overall better predictions were obtained with the anisotropy correction of Bergeles et al. [23] promoting the Reynolds stress in the lateral direction. The correction has no beneficial effect on the suction side with concave walls where the turbulence anisotropy was observed to be much smaller. This revised version was published online in July 2006 with corrections to the Cover Date.     

多圆孔圆板问题的数值解

提出了一种求解多圆孔圆板问题的新方法。首先引入了基本特解，它由主要部分和附加部分组成。主要部分为带奇点无限平板的一个特殊弹性力学解，奇点取在内圆孔的中心处。附加部分为实心圆饭的一个特解。整个基本特解满足外圆周界为自由条件。文中把待求解取为特解系的形式，其中待定系数可用变分原理得出。最后给出了算例。     

Large-eddy Simulation of Film Cooling Flows with Variable Density Jets

The present paper investigates the impact of the velocity and density ratio on the turbulent mixing process in gas turbine blade film cooling. A cooling fluid is injected from an inclined pipe at α=30° into a turbulent boundary layer profile at a freestream Reynolds number of Re_∞ = 400,000. This jet-in-a-crossflow (JICF) problem is investigated using large-eddy simulations (LES). The governing equations comprise the Navier–Stokes equations plus additional transport equations for several species to simulate a non-reacting gas mixture. A variation of the density ratio is simulated by the heat-mass transfer analogy, i.e., gases of different density are effused into an air crossflow at a constant temperature. An efficient large-eddy simulation method for low subsonic flows based on an implicit dual time-stepping scheme combined with low Mach number preconditioning is applied. The numerical results and experimental velocity data measured using two-component particle-image velocimetry (PIV) are in excellent agreement. The results show the dynamics of the flow field in the vicinity of the jet hole, i.e., the recirculation region and the inclination of the shear layers, to be mainly determined by the velocity ratio. However, evaluating the cooling efficiency downstream of the jet hole the mass flux ratio proves to be the dominant similarity parameter, i.e., the density ratio between the fluids and the velocity ratio have to be considered.     

Study on Cooling Film and Aero-Optical Effect of Hypersonic Imaging Window

Fluid Dynamics - Aerodynamic heating on the optical window of hypersonic vehicles worsen its imaging quality. The cooling efficiency and the aero-optical effect of the supersonic cooling film on...     

Tangential Slot Gas Film Cooling. Comparison of Calculation and Experiment

A method of calculating of the boundary layer in liquid rocket engine (LRE) nozzles, developed by the authors and based on a differential three-parameter turbulence model, is tested using the known experimental data for the boundary layer on a plate in zero-pressure-gradient flow with tangential gas injection. Over a wide range of both bulk flow and injected gas parameters and for variable slot geometry, the calculations for both integral and local flow and heat transfer characteristics satisfactorily agree with experiment. The study has made it possible to obtain the governing parameters which significantly affect the gas film effectiveness.     

金属薄膜短脉冲激光冲击热机耦合问题

从电子-声子相互作用的双曲型两步热传导模型出发,考虑到金属体内晶格对热传导的影响,采用有限元法,直接在时间域中求解了金属薄膜内受短脉冲激光加热的二维热机耦合问题,避免了以往因电子-声子能量方程之间的耦合关系给二维热响应问题解析求解带来的困难,提高了用数值反变换工作时计算的精度,减少了工作量,得到了金属薄膜内二维热机耦合问题的温度、位移和应力的变化规律.     

大型冷却塔的风致振动响应数值分析

风荷载是大型冷却塔建筑设计的主要荷载之一,通过风振时域分析可以全面地了解塔身的风振响应特性。本文探讨了采用线性滤波法中的自回归模型(auto-regressive,AR)模拟大型冷却塔风致振动响应的数值方法。首先根据AR模型,基于随机模拟方法,计算冷却塔表面不同高度的随机脉动风压。通过将随机脉动风压和平均风压作为冷却塔表面的外载,采用有限元分析软件计算某冷却塔的风致振动响应。结果表明,基于随机脉动风荷载模拟的数值计算方法,能正确反映冷却塔塔身的风振响应。该方法特别适用于冷却塔高度超出规范要求的情况下,评估冷却塔的风振响应。     

Numerical Modeling of Unsteady Two-Dimensional Convection in a Finite-Length Horizontal Layer Heated from Below

The development of two-dimensional thermo-gravitational convection in an elongated horizontal layer bounded by solid surfaces with the bottom instantaneously heated is investigated. The characteristics of the transition from the heat conduction regime to the convective regime are considered. The flow pattern and the heat transfer properties are described from the initial instant, which corresponds to the isothermal fluid at rest, up to the attainment of the steady-state roll-convection regime. A criterial dependence between the Rayleigh number and the nondimensional time of onset of the influence of thermo-gravitational convection on heat transfer is obtained.     

粉末注射成形中偏析效应及其影响的数值模拟

在金属或陶瓷粉末注射成形中,由于粉末与粘结剂的密度差异,二者在高速充模的过程中会产生局部比例变化,即偏析现象.针对偏析现象,采用两相流注射模型,将注射喂料视为由粉末相和粘结剂相组成的混合流体,预测注射成形坯件中粉末相和粘结剂相的分布.将结果引入到后续的烧结模拟中,宏观烧结模型采用基于热弹粘塑性的本构关系.据此模拟产品在烧结过程中发生的收缩和变形以及预测产品在烧结过程中现场强度(In-situ strength).模拟结果说明注射坯件的非匀质性导致产品的烧结过程中产生非均匀收缩和内部应力的大幅度上升,影响产品的精度和性能.这种从注射到烧结的模拟体系可用于优化粉末注射成形工艺的喂料设计、模具设计以及注射和烧结工艺参数的选取.     

Tangential Slot Film Cooling in a Nozzle. Comparison of Calculation and Experiment

To test a method of calculating the boundary layer in liquid rocket engine (LRE) nozzles, developed by the authors and based on a differential three-parameter model of turbulence, nozzle flow with tangential-slot coolant injection in subsonic part of the nozzle is studied numerically. The effect of nozzle flow acceleration on the turbulence parameters and the dependence of the gas film effectiveness on the nozzle-inlet turbulence intensity are investigated. The numerical results are compared with available experimental data.     

塑料注射成型保压过程的数值模拟

保压过程是塑料注射成开型一个重要阶段，它直接关系到最终制件的内部结构、尺寸稳定性和变形等，本文在对塑料注射成型保压过程进行深入分析的基础上，基于合理的假设和选用恰当的材料模型，导出了保压过程可压缩、非牛顿粘性流体在模具型腔中非等温流动的控制方程，采用有限元/有限差分混合法实现了对保压过程的模拟，并通过算例讨论了保压压力、浇口凝固时间、锁模力等工程关心的实际问题。     

气膜孔径向角角度对冷却效率的影响

为了探讨在不同径向角下动量比和湍流度对圆柱形气膜孔流动和换热的影响规律,采用数值模拟方法,研究了涡轮叶片的冷却效率.结果表明:随着动量比的增大,二次流出口处高温区域逐渐偏离气膜孔出口叶片的下游区域,气膜孔出口二次流的影响范围变大;二次流径向角β越大,其自气膜孔出口流出后在叶片表面的轨迹偏斜程度就越大;在湍流度保持不变的情况下,随着动量比增加,冷却效率随着x/d值的增加在总体上呈现逐渐减小的趋势;随着湍流度的增大,冷却效率先增加后减小;在动量比I≤2时,冷却效率随着湍流的增大而减小;随着径向角的增大(0°～45°范围内),冷却效率逐渐降低.     

A Numerical Investigation of Transpiration Cooling with Liquid Coolant Phase Change

This article presents a numerical approach to investigate the transpiration cooling problems with coolant phase change within porous matrix. A new model is based on the coupling of the two-phase mixture model (TPMM) with the local thermal non- equilibrium (LTNE), and used to describe the liquid coolant phase change and heat exchange processes in this article. The effects of thermal conductivity, porosity, and sphere diameter of the porous matrix on the temperature and saturation distributions within the matrix are studied. The results indicate that an increase in the porosity or sphere diameter can lead to an area dilation of two-phase region and a rise of liquid temperature; whereas an increase in the thermal conductivity of the porous matrix results only in a rise of liquid temperature, but drops of solid temperature and temperature gradient on the hot surface. The influence of hot surface pressure on cooling effect is discussed by numerical simulations, and numerical results show that the effect of the transpiration cooling will be worse under higher pressure. The investigation also discovers an inverse phenomenon to the past investigations on the transpiration cooling without coolant phase change, namely in two-phase region, coolant temperature may be higher than solid temperature. This inversion can be captured only by the new LTNE–TPMM.     

玻璃态聚合物银纹化过程的数值模拟

银纹化是玻璃态聚合物材料所特有的一种现象。本文在代表体积单元中嵌入能够刻划银纹萌生与生长的银纹单元，运用有限元方法对银纹化过程进行了数值模拟。银纹化过程中的最大主应力矢量图说明计算模型以及计算方法是比较合理的。而且，本文所揭示出来的银纹化过程的规律与实验中观察到的现象是吻合的。     

Numerical Modeling of Hydraulic Hysteresis in Unsaturated Soils

This article presents the implementation of the constitutive model of Wheeler (Geotechnique 53(1):41–54, 2003) for coupling of hydraulic hysteresis and mechanical behavior of unsaturated soils in a fully coupled transient hydro-mechanical finite element (FE) model (computer code UNSATEX) developed by the authors. The constitutive model considers the effects of irreversible changes of degree of saturation on stress–strain behavior and the influence of plastic volumetric strains on the water retention behavior. The mathematical framework and the numerical implementation of the constitutive model are presented and discussed. The FE model is verified and validated against analytical predictions [obtained using the model of Wheeler (Geotechnique 53(1):41–54, 2003] as well as experimental results from the literature involving unsaturated soils undergoing various combinations of drying, wetting, loading, unloading, and reloading paths. Comparison of the results shows that the developed FE model can be used to predict various aspects of the behavior of unsaturated soils under drying and wetting as well as loading and unloading paths. The merits and limitations of the FE model are highlighted.     

Numerical Modelling of Convection-Driven Cooling,Deformation and Fracturing of Thermo-Poroelastic Media

Transport in Porous Media - Convection-driven cooling in porous media influences thermo-poro-mechanical stresses, thereby causing deformation. These processes are strongly influenced by the...     

纳米薄膜润滑物理—数学模型及数值分析

基于润滑剂分子通常具有链状结构的事实，在分析润滑剂分子链长同膜厚关系的基础上，建立了纳米薄膜润滑物理模型，并利用含旋转量的流体力学运动方程得到了相应的Reynolds方程，同时对薄膜润滑Reynolds方程进行了数值计算，以考察特征长度对薄膜润滑状态参数的影响。结果表明，同相应的厚膜解相比，薄膜模型中润滑剂的粘度及承载能力均明显提高，且其提高幅度随着特征长度的增大而增大。根据润滑剂分子链长度确定的薄膜润滑区间以及膜厚－速度关系数值解同相应的试验结果一致。     

A Numerical Study of Laminar Reciprocating Flow in a Pipe of Finite Length

A numerical investigation has been carried out for a laminar incompressible reciprocating flow in a circular pipe with a finite length. An examination of the governing equations and boundary conditions indicates that a sinusoidally reciprocating flow is governed by three similarity parameters: the kinetic Reynolds number Re, the dimensionless oscillation amplitude A_o, and the length to diameter ratio L/D. The numerical solution for the velocity profiles of a developing reciprocating flow shows that at any instant of time, there exist three flow regimes in the pipe, namely, an entrance regime, a fully developed regime and an exit regime. The numerical results for the fully developed region are shown to be in excellent agreement with the analytical solution. Based on the numerical results, a correlation equation of the space-cycle averaged friction coefficient for a laminar developing reciprocating pipe flow has been obtained in terms of the three similarity parameters.