加力室隔热屏流场计算

加力室隔热屏流场计算赵坚行，刘全忠（南京航空航天大学动力工程系南京２１００１６）关键词隔热屏，改值计算，紊流反应流１引言本文采用数值计算的方法模拟带有隔热屏、外冷却气流、尾喷口的加力室热态流场。计算中采用修正卜。紊流模型来预估粘性系数。燃烧模型采用卜...     

空化紊流流动的数值计算模型及其验证

本文介绍了一种空化紊流流动的数值计算模型,并计算了射流放水阀内部的空化流动现象。该模型基于均相平衡模型和液相与汽相传输方程,基本方程采用N-S方程,空化模型采用Kunz等提出的汽液质量转换模型。紊流封闭采用标准的κ-ε素流模型;稳定流动计算采用扩展的SIMPLE压力修正方法,非稳定计算采用PISO算法。为评价该数值模型,计算了绕射流放水阀的空化流动,并与实验结果进行了对比,计算结果与实验结果取得较好的一致,说明该流动模型和计算方法是可靠的。     

离心泵叶轮中固液两相紊流计算

离心泵叶轮中固液两相紊流计算戴江，吴玉林，孙自祥，梅祖彦（清华大学水利水电工程系北京１０００８４）关键词固液两相流，紊流数值模拟，离心叶轮１引言离心泵在固体物料的输送中起着很重要的作用。Ｒｏｃｏ和Ｗｅｉｎｈａｒｔ利用无粘性流动的混合液模型计算了离心泵...     

组合叶栅的数值计算研究

采用混合紊流模型计算了以NACA0012为原始翼型的组合叶栅内部流场.通过计算证明,选取适当的叶栅组合参数重合度B与栅距比T,可以使组合叶栅的整体性能得到大幅度的改善.组合叶栅的整体气体性能明显优于单列叶栅的气动性能.     

轴流式喷水推进器泵级内部流场的数值计算

采用数值计算的方法,研究了轴流喷水推进器泵级模型的内部三维紊流流场和性能。计算针对泵级的进口到喷水推进器的出口进行,包括进水区域、叶轮、导流壳区域的泵级整个流道。采用结构网格对计算区域进行剖分,应用NUMECA软件对控制方程进行求解。选用Spalart-Allmaras一方程紊流模型,使用时间推进法计算流场中的流动参数。并根据流场计算结果对泵级的流量-扬程特性和流量-效率特性进行了预测。计算与实验结果对比表明,二者取得了较好的一致,说明采用的计算方法具有较好的可信性及较高的计算精度。根据流场计算结果,对泵级的性能进行了分析。     

气液两相流体绕方柱流动的数值模拟

本文详细给出了气液两相流动双流体模型下的各控制方程组和相间作用力,通过将气泡引起的紊流与剪切引起的紊流线性叠加给出了气液两相流动的紊流模型。通过给出的边界条件,采用ＩＴＡ－ＩＰＳＡ算法对垂直上升的气液两相流横向冲刷方柱引起漩涡证替脱落的过程进行了数值模拟,得到了流场和局部含气率变化的示意图,数值模拟与试验的结果基本一致。     

物体入水的光滑粒子法模拟

利用LANS-α(Lagrangian-averaged Navier-Stokes-alpha)模型对传统的光滑粒子法进行改进.通过模拟半浮力和零浮力水平圆柱的入水过程,验证改进的光滑粒子法.模拟结果与实验以及其它数值模拟结果符合的很好,表明改进的光滑粒子法适用于研究物体入水问题.     

双头部燃烧室两相燃烧流场数值研究

本文在贴体坐标系下对双头部火焰简内三维两相紊流燃烧过程进行数值模拟,采用代数雷诺应力模型模拟紊流粘性、EBU-二阶矩模型模拟燃烧反应速率、六通量辐射模型考虑热辐射对燃烧流场及火焰筒壁温的影响.分别运用颗粒轨道模型与颗粒随机轨道模型研究燃烧室内气液两相流动与燃烧过程,将所得出口温度分布与实验结果进行比较,均较为相符.     

水力振荡器式微型泵大尺度模型的数值研究

本文对水力振荡器式微型泵模型内二维紊流进行了数值模拟。文中基于雷诺平均N-S方程和κ-ε紊流模型,采用SIMPLEC算法计算了具有平板及翼型截面形状叶片的流道,得出了若干工况下流速场、叶片表面压力系数分布及叶片前后表面的压力变化;为进一步的实验研究及理论分析工作打下了基础。     

双级轴流泵内部三维紊动流场CFD分析

双级轴流泵可用作船舶的推进装置,具有推进效率高、抗空化能力强、工作平稳、噪声低等优点。采用标准k-ε紊流模型和SIMPLEC算法,对双级轴流泵内360°全流道的三维紊动流场的速度和压力分布进行数值模拟计算,并对装置的性能进行预估。计算结果与试验数据的比较表明:所采用的紊流模型和数值方法可用来描述实际流动现象。     

颗粒增强湍流的新模型和气粒流动的湍流变动

用雷诺应力方程模型和极细的网格系对单个颗粒受湍流气体绕流进行了数值模拟,研究了改变颗粒直径和气体相对速度时颗粒增强气体湍流的规律.据此构造了颗粒尾涡增强气体湍流的新模型.将此子模型加入到两相流动模型中,对竖直和水平通道内气粒两相流动进行了数值模拟,和实验结果的对照表明,考虑颗粒尾涡增强气体湍流效应得到的气体湍流脉动速度的模拟结果比不考虑此效应的模拟结果好得多.     

A modified PANS model for computations of unsteady turbulence cavitating flows

A modification to the PANS (partially averaged Navier-Stokes) model is proposed to simulate unsteady cavitating flows. In the model, the parameter f _k is modified to vary as a function of the ratios between the water density and the mixture density in the local flows. The objective of this study is to validate the modified model and further understand the interaction between turbulence and cavitation around a Clark-Y hydrofoil. The comparisons between the numerical and experiment results show that the modified model can be improved to predict the cavity evolution, vortex shedding frequency and the lift force fluctuating in time fairly well, as it can effectively modulate the eddy viscosity in the cavitating region and various levels of physical turbulent fluctuations are resolved. In addition, from the computational results, it is proved that cavitation phenomenon physically influences the turbulent level, especially by the vortex shedding behaviors. Also, the mean u-velocity profiles demonstrate that the attached cavity thickness can alter the local turbulent shear layer.     

Statistics of particle pair relative velocity in the homogeneous shear flow

Small scale clustering of inertial particles and relative velocity of particle pairs have been fully characterized for statistically steady homogeneous isotropic flows. Depending on the particle Stokes relaxation time, the spatial distribution of the disperse phase results in a multi-scale manifold characterized by local particle concentration and voids and, because of finite inertia, the two nearby particles have high probability to exhibit large relative velocities. Both effects might explain the speed-up of particle collision rate in turbulent flows. Recently it has been shown that the large scale geometry of the flow plays a crucial role in organizing small scale particle clusters. For instance, a mean shear preferentially orients particle patterns. In this case, depending on the Stokes time, anisotropic clustering may occur even in the inertial range of scales where the turbulent fluctuations which drive the particles have already recovered isotropy. Here we consider the statistics of particle pair relative velocity in the homogeneous shear flow, the prototypical flow which manifests anisotropic clustering at small scales. We show that the mean shear, by imprinting anisotropy on the large scale velocity fluctuations, dramatically affects the particle relative velocity distribution even in the range of small scales where the anisotropic mechanisms of turbulent kinetic energy production are sub-dominant with respect to the inertial energy transfer which drives the carrier fluid velocity towards isotropy. We find that the particles’ populations which manifest strong anisotropy in their relative velocities are the same which exhibit small scale clustering. In contrast to any Kolmogorov-like picture of turbulent transport these phenomena may persist even below the smallest dissipative scales where the residual level of anisotropy may eventually blow-up. The observed anisotropy of particle relative velocity and spatial configuration is suggested to influence the directionality of the collision probability, as inferred on the basis of the so-called “ghost collision” model.     

湍流黏性修正在不同孔型气膜计算中的应用

燃气轮机气膜冷却流动中的复杂涡系使得其湍流黏性系数体现出很强的各向异性。本文采用作者提出的代数各向异性湍流黏性系数修正方法(AAEV方法),对不同孔型气膜冷却进行了研究。文中结合平板圆孔、扇形孔气膜冷却实验结果,将传统的湍流模型与修正后的湍流模型获得的模拟结果与实验值进行了比较,得到修正后的结果与实验有较好的吻合度。修正后的湍流模型对不同的孔型有很好的适用性,同时揭示了两种孔不同的三维特性。     

On mean flow universality of turbulent wall flows. I. High Reynolds number flow analysis

ABSTRACT

The universality and mathematical physical structure of wall-bounded turbulent flows is a topic of discussions over many decades. There is no agreement about questions like what is the physical mean flow structure, how universal is it, and how universal are theoretical concepts for local and global flow variations. These questions are addressed by using latest direct numerical simulation (DNS) data at moderate Reynolds numbers Re and experimental data up to extreme Re. The mean flow structure is explained by analytical models for three canonical wall-bounded turbulent flows (channel flow, pipe flow, and the zero-pressure gradient turbulent boundary layer). Thorough comparisons with DNS and experimental data provide support for the validity of models. Criteria for veritable physics derived from observations are suggested. It is shown that the models presented satisfy these criteria. A probabilistic interpretation of the mean flow structure shows that the physical constraints of equal entropies and equally likely mean velocity values in a region unaffected by boundary effects impose a universal log-law structure. The structure of wall-bounded turbulent flows is much more universal than previously expected. There is no discrepancy between local logarithmic velocity variations and global friction law and bulk velocity variations. Flow effects are limited to the minimum: the difference of having a bounded or unbounded domain, and the variation range of mean velocity values allowed by the geometry.     

用动力学夸克并合描述RHIC重离子碰撞中和各相异性流和它们的标度率

We report the results on anisotropic flows and their scaling forφmesons andΩ(Ω~- ■~ )baryons in Au Au collisions at RHIC,obtained from a dynamical quark coalescence model that uses the quark phase- space information from a multi-phase transport(AMPT)model within the string melting scenario and includes the quark structure of hadrons.     

用改进的随机轨道模型数值模拟突扩液固两相流动

用改进的随机轨道模型数值模拟了突扩湍流液固两相流动。两相的轴向速度和湍动能的预报结果与实验符合得很好,同时还给出了不同计算截面上颗粒数密度和质量流量合理分布．预报结果对计算颗粒数敏感程度的研究表明：与通常的随机轨道不同,改进的随机轨道模型只需要很少的计算颗粒就可以给出合理正确的颗粒相分布。     

模型加力燃烧室燃烧流场的并行计算

本文采用基于MPI的并行算法,采用动态内存分配、分区算法和多点重合交错网格系统,在贴体网格下对带V形槽稳定器模型加力燃烧室素流化学反应流场进行数值模拟,湍流模型采用k方程亚网格尺度模型,燃烧模型采用亚网格EBU模型,采用热通量辐射模型估算辐射通量。计算结果表明并行计算对复杂形状的化学反应流动计算效率很高,是模拟大规模的燃烧问题的有力工具。     

Variable-Order Fractional Models for Wall-Bounded Turbulent Flows

Modeling of wall-bounded turbulent flows is still an open problem in classical physics, with relatively slow progress in the last few decades beyond the log law, which only describes the intermediate region in wall-bounded turbulence, i.e., 30–50 y+ to 0.1–0.2 R+ in a pipe of radius R. Here, we propose a fundamentally new approach based on fractional calculus to model the entire mean velocity profile from the wall to the centerline of the pipe. Specifically, we represent the Reynolds stresses with a non-local fractional derivative of variable-order that decays with the distance from the wall. Surprisingly, we find that this variable fractional order has a universal form for all Reynolds numbers and for three different flow types, i.e., channel flow, Couette flow, and pipe flow. We first use existing databases from direct numerical simulations (DNSs) to lean the variable-order function and subsequently we test it against other DNS data and experimental measurements, including the Princeton superpipe experiments. Taken together, our findings reveal the continuous change in rate of turbulent diffusion from the wall as well as the strong nonlocality of turbulent interactions that intensify away from the wall. Moreover, we propose alternative formulations, including a divergence variable fractional (two-sided) model for turbulent flows. The total shear stress is represented by a two-sided symmetric variable fractional derivative. The numerical results show that this formulation can lead to smooth fractional-order profiles in the whole domain. This new model improves the one-sided model, which is considered in the half domain (wall to centerline) only. We use a finite difference method for solving the inverse problem, but we also introduce the fractional physics-informed neural network (fPINN) for solving the inverse and forward problems much more efficiently. In addition to the aforementioned fully-developed flows, we model turbulent boundary layers and discuss how the streamwise variation affects the universal curve.