迷宫汽封与平衡孔在透平级中应用的仿真研究

为了进一步认识匹配应用迷宫汽封和平衡孔对透平级气动性能的影响,采用商用软件CFX,数值仿真了某汽轮机高压一级半透平、堵住平衡孔的一级半透平内部的三维流场.通过对计算结果的比较分析发现,转子带凸台的高低齿迷宫式汽封,与转子外径相等、同压比的等齿高直通型迷宫汽封相比,泄漏流动的方向折转以及在汽封腔内形成的旋涡显著增多,因此强化了对泄漏流的阻抗及其动能的耗散,提高了汽封的封严性.对于低反动度透平级,气流对动叶栅的直接冲击是级内轴向力产生的主要原因.叶冠的径向高度远小于叶高,但是叶冠产生的轴向力在级轴向力中占有较大比例.平衡孔需要与前后静叶隔板汽封以及动叶前后轴向间隙汽封匹配设计,设计合理,能够消除泄漏流对主流的干扰,降低透平级的流动损失.     

考虑汽封条件下汽轮机调节级多工况的数值研究

具有部分进汽特性的汽轮机调节级,其动叶围带顶部汽封齿后的泄漏流动同主流的相互作用,不仅影响机组的气动性能和效率,而且对机组的安全稳定性也有一定影响。基于三维黏性可压缩的Navier-Stokes方程对某150MW汽轮机调节级进行了全三维的数值模拟,建立了安装汽封齿全周流动模型,对不同进汽度下的汽轮机调节级内部流场进行了数值研究。结果表明:处于进汽段的动叶栅其流量和动叶扭矩都比较大,汽封内部流动总体是按照从动叶前缘向后缘的流动;而处于非进汽段的动叶栅,内部汽体基本处于呆滞状态,甚至存在蒸汽对动叶的扭矩为负值的情况,汽封内的流动方向改变,从动叶后缘向前缘发展。随着部分进汽度的降低,泄漏比例则显著增大,而轮周效率显著降低。     

叶轮带平衡孔的汽轮机级内蒸汽流动仿真分析

针对某200MW冲动式汽轮机组低压缸叶轮开设平衡孔的第二级内部流动状况进行有限元分析,分析结果表明:该级出现了负的反动度,叶轮后流体压力大于叶轮前流体压力,导致该级叶轮出现负的轴向推力,能平衡掉部分工作汽流产生的正的轴向推力,但直平衡孔的结构减少了平衡轴向推力的轴向投影面积,削弱了平衡正轴向推力的效果;在级的流线云图中...     

汽轮机调节级多工况下三维流场数值研究

汽轮机调节级的部分进汽特性,不仅影响到机组的气动性能和效率,而且还对其安全性产生一定程度的影响。基于三维黏性可压缩雷诺时均Navier-Stokes(N-S)方程,采用结构化六面体网格,运用有限容积法,构造了带有进汽室和加强筋的300MW汽轮机调节级三维黏性可压缩计算模型,针对不同运行工况下调节级内部复杂流动进行了详细研究。分析发现:调节级进汽室内部流动损失较大;进汽段下游动叶通道静压分布合理,内部流动顺畅,而非进汽段动叶通道内部流动紊乱,熵增明显,部分进汽带来的损失较大;部分进汽度越小,效率降低越快,尤其是一阀进汽时,效率急剧下降。     

汽轮机部分进汽调节级三维流场的非定常数值模拟

使用商业软件NUMECA,采用三维粘性数值模拟方法对处于部分进汽条件下调节级的内部流动进行数值模拟,并以此来分析调节级内部流动的非定常现象,从而进一步理解调节级的工作机理.     

汽轮机调节级三维复杂流动的数值研究

汽轮机调节级的部分进汽特性,不仅对机组的气动性能和效率具有较大的影响,还在一定程度上影响到其安全性能.基于三维黏性可压缩N-S方程,采用结构化六面体网格,运用有限容积法,构造了带有进汽室的150 Mw汽轮机调节级三维黏性可压缩计算模型,对其内部复杂流动进行了详细研究.分析发现:由于部分进汽.调节级进汽室内部流动较为紊乱...     

汽轮机补汽阀结构设计数值模拟研究

补汽阀技术是一项提高机组调频灵活性、提高效率和可靠性的成熟技术,大功率汽轮机组常采用补汽调节阀技术来提高输出功率。补汽会影响汽轮机内部蒸汽流动,使级的气动性能降低。针对汽轮机补汽对主通道蒸汽流动的影响,参考某660MW汽轮机补汽阀结构,建立三维数值计算模型,研究补汽结构的流场分布情况,分析补汽对汽轮机级气动性能的影响,提出切向-轴向进汽补汽结构模型。数值计算结果表明:相比于径向进汽模型,切向-轴向模型能使补汽后一级静叶环形截面速度和压力分布均匀程度得到明显改善,这有利于提高汽轮机级效率。     

600MW汽轮机组高压联合进汽阀变工况内部流场的特性分析

采用数值模拟方法对某600 MW汽轮机高压联合进汽阀的内部流动进行了分析.通过求解全三维N-S方程和k-ε湍流模型,得到了阀门内部的流场特性.在3种不同负荷下对主汽阀全开、调节阀阀门不同开启顺序时的流场进行模拟,并分析了流动损失产生的机理.结果表明:调节阀B的流量比调节阀A大,流动状态比调节阀A好;先开启调节阀B后开启调节阀A时,各截面的压损小,各阀门的流动状态好.     

低压缸进汽蜗壳气动性能试验研究

为了研究汽轮机低压缸进汽蜗壳气动性能,将某机组低压进汽蜗壳进行吹风实验研究.分析发现周向速度在三维速度矢量中占据主导,带导流结构出口速度更均匀,不带导流气流角更均匀,进汽蜗壳的流动损失随流量增加而上升,横置导叶全周进口流场不均匀,且随着流量的增大而增强.     

600MW汽轮机组高压联合进汽阀变工况内部流场的特性分析

采用数值模拟方法对某600 MW汽轮机高压联合进汽阀的内部流动进行了分析.通过求解全三维N-S方程和k-ε湍流模型,得到了阀门内部的流场特性.在3种不同负荷下对主汽阀全开、调节阀阀门不同开启顺序时的流场进行模拟,并分析了流动损失产生的机理.结果表明:调节阀B的流量比调节阀A大,流动状态比调节阀A好;先开启调节阀B后开启调节阀A时,各截面的压损小,各阀门的流动状态好.     

Flow channel design in a proton exchange membrane fuel cell: From 2D to 3D

Flow channel design has attracted more and more attention with the evolution of fuel cell technology. Compared with conventional 2D flow channel, 3D flow channel has been proved to improve the performance of proton exchange membrane fuel cell with great enhancement of reactant transport in many researches. In this paper, flow fields of parallel 2D, simplified 3D and 3D with inclination are presented to study the transport and distribution characteristics of reactant and water inside a fuel cell, and efficiency evaluation criterion is proposed to evaluate the superiority of the flow channel design. It is found that 3D flow fields are superior compared with parallel 2D flow channel, with improved capacity of mass transfer, uniform water distribution and advanced water removal ability. The performance improvements of both 3D flow channel designs become significant at elevated current density, with the output voltage increasing to 4.4% at 1.6 A cm^?2 and up to 10% at 2 A cm^?2. Compared with 3D flow channel with inclination, simplified 3D flow channel shows smaller pressure drop, and it has better performance than that of 2D flow channel. Considering both the performance and flow resistance, simplified 3D flow channel performs the best with high efficiency and easy-processing, thus it is the future direction of flow design.     

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.     

Volumetric interfacial area prediction in upward bubbly two-phase flow

In two-phase flow studies, a volumetric interfacial area balance equation is often used in addition to the multidimensional two-fluid model to describe the geometrical structure of the two-phase flow. In the particular case of bubbly flows, numerous works have been done by different authors on the subject. Our work concerns two main modifications of this balance equation: (1) new time scales are proposed for turbulence induced coalescence and breakup, (2) modeling of the nucleation of new bubbles on the volumetric interfacial area. The 3D module of the CATHARE code is used to evaluate our new model, in comparison to three other models for interfacial area found in the literature, on two different experiments. First, we use the DEBORA experimental data base for the comparison in the case of boiling bubbly flow. The comparison of the different volumetric interfacial area models to the DEBORA experimental data shows that even though the theoretical values of the coefficients are adopted in our modified model, this model has a quite good capability to predict the local two-phase geometrical parameters in the boiling flow conditions. Secondly, we compare the predictions obtained with the same models to the DEDALE experimental data base, for the case of adiabatic bubbly flow. In comparison to the other models tested, our model also gives quite good predictions of the bubble diameter in the case of adiabatic conditions.     

叶轮机械叶片气动设计流程的改进研究

本文讨论了准三维S1、S2流面迭代及全三维流场计算的特点,对叶轮机械气动设计流程中的S1计算部分作了改进:通过定量分析全三维流场计算结果并从中提取若干S1流面上的物理参数,反馈给S2流面计算进行迭代以及修改叶片造型,将多个S1流面的计算与全三维校核融为一体,从而简化了设计流程,并提高设计的准确性.按照改进的流程设计了一...     

Hyperbolically Shaped Centrifugal Compressor

Starting from the classical centrifugal compressor, cone shaped in meridional cross section, two modifications are considered on the basis of results from 2D and 3D flow models. The first modification is the change of the meridional cross section to hyperbolically shaped channel. The second modification, proposed on the basis of 2D axisymmetric solution, concerns the shape of blading. On the strength of this solution the blades are formed as 3D shaped blades, coinciding with the recent tendency in 3D designs. Two aims were considered for the change of meridional compressor shape. The first was to remove the separation zone which appears as the flow turns from axial to radial direction. The second aim is to uniformize the flow at exit of impeller. These two goals were considered within the frame of 2D axisymmetric model. Replacing the cone shaped compressor by a hyperbolically shaped one, the separation at the corner was removed. The disc and shroud shape of the compressor was chosen in the way which sat     

多级轴流压气机气动设计体系的国内外研究进展

轴流压气机设计体系对压气机的设计周期和性能有着重要影响。为了能够更好地了解轴流压气机设计体系的发展情况,本文对其进行了整理综述。首先,结合轴流压气机涉及到的设计方法,对国内外轴流压气机设计的发展过程进行了介绍,主要包括一维二维设计体系、准三维设计体系和全三维流场计算模拟技术;然后,在整理完整设计体系要求的基础上,简述了国内外现有比较完整的轴流压气机设计体系。就目前发展来看,随着工程要求的不断提高以及计算机技术的提升,全三维流场计算模拟技术势必会成为今后的发展焦点,各公司和研究机构也在此基础上对原有的设计体系开展技术攻关。     

CFD技术在汽油机进气歧管优化设计中的应用

在发动机设计开发过程中,需要评估进气歧管是否满足进气均匀性的标准。首先利用1D-3D耦合方法计算得到进气歧管的平均质量流量,然后将其作为三维数值计算的输入边界。利用fire软件对初始进气歧管进行CFD分析,计算出各缸的流量系数及其偏差。针对存在压力损失的部位进行优化,直到其进气均匀性满足标准。结果表明:通过1D-3D耦合方法可以为三维数值计算提供准确的输入边界;通过CFD方法可以发现进气歧管结构中对流动不好的部位;通过CFD方法进行优化设计分析已经成为进气歧管设计过程中的重要手段。     

3D hybrid Cartesian/immersed-boundary finite-element analysis of heat and flow patterns in a two-roll mill

A fully three-dimensional time-dependent Navier–Stokes model with forced convection is developed to numerically investigate the heat and flow patterns of the two-roll mill system with two inner rotating cylinders. Such direct numerical simulations are usually limited by the difficulties from huge computational cost and complex boundary treatment. For a fast numerical process, we can use the operator-splitting scheme with the BTD term to advance the solution in temporal evolution. To implement the calculation over a Cartesian grid, the hybrid Cartesian/immersed-boundary finite-element method is employed for spatial discretization. In the authors’ previous study [D.L. Young, C.L. Chiu, C.M. Fan, A hybrid Cartesian/immersed-boundary finite-element method for simulating heat and flow patterns in a two-roll mill, Numer. Heat Transfer B 51 (3) (2007) 251–274], we have developed a simplified 2D numerical model to analyze the heat and flow patterns on the cross section of two-roll-mill flow under the assumption of infinite length in the third (vertical) direction. However, the 2D solutions could not completely represent the realistic physical phenomena unless a 3D algorithm is developed. In this study we then paid the particular attention to develop a 3D model to investigate the vertical heat and flow behaviors, including 3D features of the vortex structure, periodic oscillation and chaotic instabilities. It is found that the proposed 3D model is able to cover the 2D features if the assumptions of 2D conditions are fulfilled.     

Mathematical modeling and optimization of hydrogen distribution network used in refinery

In the present investigation, mathematical models have been developed to optimize hydrogen distribution in the refinery. Five models, Model-0, Model-1, Model-2, Model-3 and Model-4, have been formulated to determine the optimal hydrogen network. Amongst these, Model-0 and Model-1 are NLP networks, whereas the remaining three are MINLP networks. The NLP models are improved gradually to develop MINLP models which incorporate new compressor and PSA. The model considers pressure constraints, source flow balance, sink flow balance, compressor flow balance, sink purity constraint, operating cost, capital cost associated with new equipment, payback period and export cost. Amongst five models, Model-4 is predicted as optimal network which is MINLP model incorporating new compressor and PSA. It predicts reduction in hydrogen by 21.74% and annual profit of $ 16.57 million. The present work selects the optimal type of new compressor based on different capital cost functions. Further, the reliability of the present work is checked through comparison of its results with published models.