EXPERIMENTAL STUDIES ON SWIRLING AND RECIRCULATING TWO-PHASE FLOW FIELD IN A COLD MODEL OF DUAL-INLET SUDDEN-EXPANSION COMBUSTOR

The axial and tangential velocities of gas and particle phases and particle concentration for turbulent swirling and recirculating gas-particle (simulating gas-droplet) flows in a cold model of a dual-inlet sudden-expansion combustor with partially tangential central tubes, proposed by the present authors, were measured by using a 2-D LDV system and a laser optic fiber system combined with a sampling probe. The results show that there are both gas and particle strongly reverse flows and swirling flows in the head part of the combustor. The velocity slip between gas and particle phases is remarkable. The particle concentration is higher near the wall and lower near the axis. There are two peaks in the concentration profiles near the inlet tubes. The above-obtained flow characteristics are favorable to ignition, flame stabilization and combustion. The results can also be used to validate the numerical modeling.     

扑动翼型的低雷诺数气动特性分析

通过求解引入拟压缩项的不可压Navier-Stokes方程,数值模拟了绕扑动翼型的低雷诺数非定常流动。针对厚度在4%-12%之间的NACA对称翼型,分析了翼型厚度等参数对扑动翼型气动特性的影响。在低雷诺数条件下,对于纯俯仰运动,随着翼型厚度的减小,平均阻力系数也变小。而对于纯沉浮运动,发现翼型厚度对气动特性的影响和俯仰运动有很大的差别,平均阻力系数随着翼型厚度的减小而变大。通过对沉浮运动一个周期流线图的分析,认为这是翼型前缘涡的影响造成的。由于前缘涡的影响,翼型厚度增加,平均压差阻力系数变小,甚至会出现负值。雷诺数的影响研究表明,随着雷诺数的增加,扑动翼型的阻力系数减小的趋势越缓慢。     

Local stability analysis of interface region of astrophysical viscous shear flows with a gradual velocity gradient

In this paper, we extend the stability analysis of cold sharp shear flows to warm astrophysical cases with, inevitable, gradual velocity gradient in the interface region in the presence of viscosity effect. Using linear perturbation theory as well as the local approximation method, the instability growth rate of the excited electromagnetic modes has been investigated for the relativistic and non-relativistic cases of solar wind interacting with interstellar plasma medium. Results show that astrophysical shear systems with a small velocity gradient in the transition region are more stable rather than larger ones. Moreover, dependent on the viscosity coefficient value, the viscosity effects could have a positive role on the instability growth rate of the system in some range of initial bulk velocity, while it plays a destructive role in other velocity ranges.     

A new two-scale model for large eddy simulation of wall-bounded flows

A new hybrid approach to model high Reynolds number wall-bounded turbulent flows is developed based on coupling a two-level simulation (TLS) approach (Kemenov and Menon, 2006 [1], 2007 [2] in the inner region with conventional large eddy simulation (LES) away from the wall. This new approach is significantly different from previous near-wall approaches for LES. In this hybrid TLS–LES approach, a very fine small-scale (SS) mesh is embedded inside the coarse LES mesh. The SS equations capture fine-scale temporal and spatial variations in all three Cartesian directions for all three velocity components near the wall. The TLS–LES equations are derived using a new scale separation operator that allows a smooth transition between the two regions, with the equations in the transition region obtained by blending the TLS large-scale and LES equations. New terms in the hybrid region are identified. The TLS–LES approach is used to study the near-wall features in canonical turbulent channel flows for a range of Reynolds number using relatively coarse large-scale (LS) grids. Results show that the TLS–LES approach is able to capture the effect of both the LS and SS features in the wall region consistently for the range of simulated Reynolds number.     

求解最小费用最大流问题的一种方法

介绍了最大流问题的多解，提出了通过调整圈来求解最小费用最大流的方法。     

用非线性k-ε-k_p两相湍流模型模拟旋流两相流动

建立了两相湍流的代数应力模型 ,并由此出发 ,导出非线性k ε kp 两相湍流模型 ,目的是合理地模拟各向异性较强的旋流两相流动 ,保持二阶矩模型的优点 ,同时比二阶矩模型简单 .文中得到了气相、颗粒相的雷诺应力和两相脉动速度关联的非线性应力应变关系式。这些代数式和两相各自的湍动能k ,kp,以及两相脉动关联湍动能kpg的方程联立 ,就构成非线性k ε kp 模型 .将该模型用于模拟旋流两相流动 ,给出两相时均速度场及雷诺应力各分量 ,并且将模拟结果和实验数据以及二阶矩模型的模拟结果对照 .研究结果表明 ,该模型预报旋流两相流动的能力和二阶矩模型的能力相差不多 ,但计算量比二阶矩模型的小     

定常可压缩无粘流非线性方程解的完全边界积分表示式

 本文以ρV为因变量将可压缩等熵无粘流非线性方程的解表示成完全边界积分形式,从而将问题的计算维数降低一维。     

球锥俯仰阻尼导数的数值计算

本文从非定常Ｅｕｌｅｒ方程出发，应用谐振摄动法计算了球锥体超声速、高超声速下的俯仰阻尼导数和。Ｅｕｌｅｒ方程的求解利用ＳＣＭ方法和ＭａｃＣｏｒｍａｃｋ的两步算法。文中用任意攻角下不同俯仰轴的气动导数转换公式来简化计算，用较粗网格可以得到较精确的结果，程序编制相对简单。一次计算可以得到定常绕流解及一系列钝头率、不同俯仰轴下的多种动导数结果，在ＥＬＸＳＩ６４００机上约需２０～４０分钟。所得结果与试验结果符合程度令人满意。     

高阶精度非线性格式WCNS-E-5在二维流动中的应用研究

本文采用具有5阶精度的加权紧致非线性显式格式(WCNS-E-5)对定常与非定常二维流动进行数值模拟,研究表明该格式对各类间断有很好的分辨捕捉能力,而且对强间断如激波的计算,即使在高马赫数与高雷诺数条件下它仍具有很好的收敛性与可靠的计算结果.此外,WCNS-E-5在粗网格条件下也体现出优越性.类如WCNS-E-5的高精度激波捕捉方法将为以后开展湍流数值模拟工作提供坚实的技术保证.     

低雷诺数翼型和跨声速翼型边界层计算

本文利用边界层动量积分方程和平均流动能积分方程兼容计算了翼面的层流和湍流边界层流动。文中采用一种e~9型转捩判别公式预测翼面存在层流分离气泡情况的转捩位置。并引入对剪应力系数C_r的滞后方程以体现湍流中雷诺应力的历程效应。为避免在翼面流动分离时边界层方程的奇异,采用反解法计算。算例表明,计算与测量结果吻合良好。