拟压缩性方法数值模拟绕弹体的不可压缩层流脱体涡流动

本文应用在连续生方程中增加压力对时间导数项的拟压缩性方法，数值求解三维定常不可压缩Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程。数值求解过程采用隐式的Ｂｅａｍ－Ｗａｒｍｉｎｇ近似因式分解格式。计算绕尖头旋成柱体的大迎角脱体涡流动，得到与实验相符的结果。     

Features of mass supply and flows related with reconnection in the solar corona

Symmetrical broadening in the emission spectral lines is the ultimate observational effect of magnetic reconnection in the solar corona. Reconnection can create plasmas of very different temperatures and, hence, very different electrical conductivities in the corona. The electrodynamical effect of such a mass supply is considered. Electromagnetic expulsion force, different from Parker's well-known magnetic buoyancy force, can effectively balance gravity in prominences and generate fast vortex flows in the vicinity of fine threads inside prominences. The possibility of observing this effect from SOHO is discussed.     

应用傅里叶时间谱方法求解二维跨音速流动问题解的精度研究

为了从时间离散精度的角度评估傅里叶时间谱方法的实际计算效率,对用该方法求解二维跨音速流动问题的解进行了精度研究。通过求解Euler方程模拟俯仰振动NACA0012翼型的周期性非定常流动。结果表明:傅里叶时间谱方法可以使用很大的时间间隔较为准确地模拟有激波存在的周期性跨音速流动;对于此类流动问题,相比二阶向后差分公式法,傅里叶时间谱方法在预测翼型表面压力系数积分量特别是升力系数的时间变化规律方面具有明显的计算效率优势;用于模拟翼型表面压力系数自身的时间变化规律时,傅里叶时间谱方法具有不低于二阶向后差分公式法的计算效率。     

大功率氧煤燃烧器内湍流气固两相流动数值模拟

本文对新型同轴射流缩口式氧煤枪所组成的大功率氧煤燃烧器内冷态轴对称二维湍流气固两相流动用ｋ－ｅ－ＡＰ两相湍流模型进行了数值预报，揭示了燃烧器内两相流场特征，预报结果和实验结果相符。进一步对相应高炉实际工况高速条件下的冷态两相流场进行了预报，其结果为优选结构尺寸和流动参数提供了重要依据。     

Shear Flow Instabilities in Low-Beta Space Plasmas

We study instabilities driven by a sheared plasma flow in the low-frequency domain. Two unstable branches are found: the ion-sound mode and the kinetic Alfvén mode. Both instabilities are aperiodic. The ion-sound instability does not depend on the plasma β (gas/magnetic pressure ratio) and has a maximum growth rate of about 0.1 of the velocity gradient dV ₀/dx. On the other hand, the kinetic Alfvén instability is stronger for larger β and dominates the ion-sound instability for β > 0.05. Possible applications for space plasmas are shortly discussed.     

低马赫数流动数值模拟方法的研究

在文献[1，2]提出的一种低马赫数流动数值模拟新方法的基础上，本文作者进一步优化了算法，确定了该方法适用的马赫数范围，讨论了参数σ对计算的影响。大量的定常／非定常、低雷诺数流动的计算结果表明这种方法具有计算精度高、收敛速度快以及计算花销小的特点。     

有攻角细长旋成体极端地面效应分析

本文用匹配摄动方法研究了细长旋成体贴近地面运动时诱导的不可压缩势流问题,它是经典细长体理论的推广和发展。文中将流场分为内外两个渐近区域,建立了问题的匹配摄动理论,并利用文献[1]中的双圆诱导不可压缩势流的精确解,给出了该问题的首阶解析解。然后又导出了细长体上的吸力和俯仰力矩的计算公式。在此基础上,文中对细长旋成体极端地面效应的运动学规律和动力学规律作了定性和定量两个方面的分析。     

Computational engineering analysis of external geometrical modifications on MQ-1 unmanned combat aerial vehicle

This paper focuses on the effects of external geometrical modifications on the aerodynamic characteristics of the MQ-1 predator Unmanned Combat Aerial Vehicle (UCAV) using computational fluid dynamics. The investigations are performed for 16 flight conditions at an altitude of 7.6 km and at a constant speed of 56.32 m/s. Two models are analysed, namely the baseline model and the model with external geometrical modifications installed on it. Both the models are investigated for various angles of attack from −4° to 16°, angles of bank from 0° to 6° and angles of yaw from 0° to 4°. Due to the unavailability of any experimental (wind tunnel or flight test) data for this UCAV in the literature, a thorough verification of calculations process is presented to demonstrate confidence level in the numerical simulations. The analysis quantifies the loss of lift and increase in drag for the modified version of the MQ-1 predator UCAV along with the identification of stall conditions. Local improvement (in drag) of up to 96% has been obtained by relocating external modifications, whereas global drag force reduction of roughly 0.5% is observed. The effects of external geometrical modifications on the control surfaces indicate the blanking phenomenon and reduction in forces on the control surfaces that can reduce the aerodynamic performance of the UCAV.     

Revisiting the space-time gradient method: A time-clocking perspective,high order difference time discretization and comparison with the harmonic balance method

This paper revisits the Space-Time Gradient (STG) method which was developed for efficient analysis of unsteady flows due to rotor–stator interaction and presents the method from an alternative time-clocking perspective. The STG method requires reordering of blade passages according to their relative clocking positions with respect to blades of an adjacent blade row. As the space-clocking is linked to an equivalent time-clocking, the passage reordering can be performed according to the alternative time-clocking. With the time-clocking perspective, unsteady flow solutions from different passages of the same blade row are mapped to flow solutions of the same passage at different time instants or phase angles. Accordingly, the time derivative of the unsteady flow equation is discretized in time directly, which is more natural than transforming the time derivative to a spatial one as with the original STG method. To improve the solution accuracy, a ninth order difference scheme has been investigated for discretizing the time derivative. To achieve a stable solution for the high order scheme, the implicit solution method of Lower-Upper Symmetric Gauss-Seidel/Gauss-Seidel (LU-SGS/GS) has been employed. The NASA Stage 35 and its blade-count-reduced variant are used to demonstrate the validity of the time-clocking based passage reordering and the advantages of the high order difference scheme for the STG method. Results from an existing harmonic balance flow solver are also provided to contrast the two methods in terms of solution stability and computational cost.     

进口速度和含气率对气泡-液体两相湍流影响的数值研究

气泡-液体两相湍流规律的一个重要问题是,气泡究竟是加强还是削弱液体湍流,或者何时加强何时削弱液体湍流,尚有待深入探讨.本文用作者们提出的二阶矩液体-气泡两相湍流模型即两相雷诺应力方程模型模拟了二维通道内气泡-液体闭式多股射流在不同含气率和不同进口速度下的气泡和液体湍流脉动速度.预报结果和文献中给出的实验结果趋势一致.研究结果显示出低含气率及低进口速度下气泡增强液体湍流,高含气率及高进口速度下气泡削弱液体湍流的规律,澄清了众说纷纭的看法.