涡喷热融除冰流场数值模拟

涡喷发动机产生的高温高速尾气被导气罩引致喷嘴,以320m/s的喷射速度、873K的高温和102.4m3/s的流量喷射地面冰层,以清除重要和关键场所的路面薄冰层。使用计算流体力学方法,数值模拟分析了单相流形成的压力场、速度场和温度场,以及冰融后形成的水雾粒子在两相流场中的分布、速度和运移状态。数值模拟结果表明,高温高速喷射气流所形成流场的温度场,高温层与冰层直接接触,路面薄冰快速形成水雾;水雾与气流混合形成高密度固相梯度分布的高速移动两相流,瞬时移出计算域以外。涡喷除冰实践和数值模拟结果均验证了涡喷热融除冰的快速有效性。     

机翼积冰对机翼动态特性的影响

针对某型飞机机翼积冰后机翼性能改变问题,提出了一种基于流场和结构场耦合分析的机翼结构特性方法。该方法应用有限元法对二维定常不可压粘流的时均N-S方程进行离散求解,采用四阶龙格-库塔(RK)法求解水滴运动方程确定积冰污染程度,通过与未污染时的机翼特性和安全飞行包线指标对比,分析机翼积冰对机翼动态特性的影响。算例说明了该方法的有效性。     

基于数值模拟方法的机翼上反角研究与设计

针对某大展弦比、上单翼、低速飞机,利用数值模拟技术,对其机翼上反角的空气动力特性进行研究。数值模拟结果表明:机翼上反角对该类飞机升阻特性及俯仰力矩特性影响较小,上反使升力略有损失;对横航向空气动力特性影响较大,尤其是对横向静稳定性影响较为显著,上反角每增加1°横向静稳定性Clβ约增加18.7%,而下反角则降低了横向静稳定性;对航向静稳定性略有影响,上反角使Cnβ略有降低,下反角使Cnβ稍有增加。以上结论可作为同类飞机初步设计或改进改型时的参考和依据。     

节能离心泵全流道内部湍流的动态大涡模拟

应用不可压缩流体N-S控制方程和大涡模拟动态亚格子湍流模型,基于非结构网格和滑移网格技术,采用SIMPLEC算法实现速度、压力变量的分离求解,得到了某新型离心泵从进口到出口的全流道各过流部件的速度场和压力场分布,与k-ε模型计算结果比较表明,采用动态大涡模拟方法对离心泵内部流场预测更加精确、合理.     

非光滑表面对汽车尾涡结构的控制分析研究

车身气动阻力直接影响汽车的动力性和燃油经济性,尾涡结构对于车辆空气阻力的形成有很大的影响,非光滑结构在车身的合理布置能有效地减小汽车的空气阻力。为了研究车身非光滑结构对汽车尾涡结构的影响与控制,将凹坑型非光滑单元分别布置在MIRA阶梯背模型尾部、顶部、行李舱盖等表面,运用计算流体力学(Computational fluid dynamics,CFD)数值仿真与风洞试验相结合的方法,对比分析车身表面光滑模型与车身表面非光滑模型尾部流场的压力、湍流耗散率、速度矢量等参数的影响,探讨非光滑结构的扰动效应及其对尾涡形成的控制作用,得出非光滑结构能延迟气流分离,控制后风窗上猫眼涡与尾部剪切涡流,也能抑制汽车尾部主涡的生成。为有效控制车辆尾迹中旋涡结构,抑制涡激振动,改善汽车气动特性提供重要依据。     

叶轮机械三维弯叶片粘性流场的数值模拟

提出了一种在时间方向具有二阶精度的隐式方法,该方法是关于ｎ个标量方程的隐式算式,算法简单。利用此方法对三维弯叶片定常粘性流场进行了数值模拟,成功地捕捉到了流场中的各种波系和涡系结构。通过与直叶片流场中的涡系结构对比发现,弯叶片降低损失的另一个主要原因是弯叶片能将对二次流起主要作用的通道涡限定在一个稳定的范围内     

螺旋离心泵管路内流的数值模拟研究

文中采用现代计算流体动力学(CFD)的计算方法,对螺旋离心泵的管路内部流动的实际流场进行了数值模拟,并给出了流场控制、颗粒在流体中的运动和受力的求解方程式,最后对计算结果进行了分析。     

内啮合齿轮泵流场的数值模拟

采用Fluent的动网格技术,对内啮合齿轮泵内部流场进行了二维非定常计算,得到了内啮合齿轮泵在不同工况下的流场特性。结果表明内啮合齿轮泵无困油现象,泵转速提高会使压力过渡区相邻两齿之间的压差增大。     

涡管分离器流场的数值模拟及试验研究

分析了湍流中的计算流体动力学ＣＦＤ模型。用介于ＡＳＭ和ＲＳＭ之间的一个混和模型，对涡管分离器中的流场进行了理论计算，得出了涡管分离器中的流场分布规律。然后用激光多普勒装置试验测试了分离器中的速度分布，揭示了在涡管分离器底部有强烈的方向向内的径向流动。这对涡管分离器的优化设计有着重要意义。     

单、双类圆柱型杆件绕流的大涡模拟研究

通过建立不同拔模角的渐变截面正圆柱型、斜体圆柱型杆件以及阶梯圆柱杆件模型,包括单杆件与双杆件,采用大涡模拟的数值方法,采取涡粘性亚格子Smagorinsky模型封闭方程,对高雷诺数下类圆柱型杆件的绕流流动进行研究。在增加横向速度的条件下,分析了各类杆件模型气动载荷的时域、频域特性,得到了阻力系数、升力系数、周向压力系数的分布规律;分析了尾流漩涡的变化规律,以及由于涡的交替脱落导致的杆件壁面压力的变化。计算结果表明单杆件模型中当拔模角增大时阻力系数的幅值在时间周期上延后出现且幅值减小;双杆件模型中则是拔模角为3°的工况,但斜体放置时拔模角为1°主频最大,同时存在低频的峰值。周期内涡旋脱落产生一个周期升力变化的同时,产生1.5个周期的阻力变化。在气动载荷中升力系数受复杂工况的影响最大,阶梯圆柱型杆件的气动力稳定性较好。拔模角及横向风速影响杆件尾流的分布规律,使得涡的脱落点沿倾角及横向风速的下游方向偏移。     

Numerical simulation of the aeroacoustic noise in the separated laminar boundary layer

The unsteady flow characteristics and the related noise of separated incompressible laminar boundary layer flows (Re _δ*=614, 868, and 1,063) are numerically investigated. The characteristic lines of the wall pressure are examined to identify the primary noise source, related with the unsteady motion of the vortex at the reattachment point of the separation bubble. The generation and propagation of the vortex-induced noise in the separated laminar boundary layer are computed by the method of Computational Aero-Acoustics (CAA), and the effects of Reynolds number, Mach number and adverse pressure gradient strength are examined.     

Experimental verification and numerical simulation of a vortex flowmeter at low Reynolds numbers

This study presents experimental verification and numerical simulations of a vortex flow meter in the Reynolds number range between 8300 and 50,000. A custom-designed bluff body with a wedge back shape was used in the flowmeter. A shedding frequency of the flowmeter was measured in an air duct using a hot-film probe. To evaluate the accuracy of the flowmeter, a measurement uncertainty analysis was performed. Numerical simulations of the vortex flowmeter were performed with the open source code OpenFOAM. Transient simulations of periodic vortex shedding behind the bluff body were performed using different simulation methods depending on the pipe Reynolds number, such as Direct Numerical Simulation (DNS), Large Eddy Simulation (LES) and Unsteady Reynolds Averaged Navier Stokes (URANS) method. The simulated vortex shedding frequencies matched the experimental data very well. Experiments and simulations demonstrated a clear linear dependence of the shedding frequency on the volumetric flow rate over the entire range of Reynolds numbers. In addition, numerical simulations were used to study the main mechanisms of vortex formation and shedding behind the considered bluff body.     

Influence of blockage and shape of a bluff body on the performance of vortex flowmeter with wall pressure measurement

Experimental and numerical investigations are carried out with various bluff body shapes to identify an appropriate shape which can be used for vortex flowmeter application. In both the cases vortex shedding frequency is inferred from the fluctuation of wall pressure. The numerical simulations are carried out with cylindrical and triangular bluff bodies to understand the vortex shedding phenomenon and to identify an appropriate turbulence model for this class of flows with wall pressure measurement. The simulations reveal that the k-ε RNG model predicts the Strouhal number closer to the experimental results than other models. The experimental investigations are carried out with several bluff body shapes, such as triangular, trapezoidal, conical, cylindrical and ring shapes, with water as the working medium. In this context, the effects of sampling rate, tap location and blockage effects are explored. The results suggest that the axisymmetric tapping is better than differential pressure tapping in terms of signal amplitude. The non-dimensional location of the static pressure tap is found to be 0.714 times diameter of pipe times blockage. The trapezoidal bluff body is found to be the best among all the bluff bodies investigated in terms of signal amplitude and constancy of Strouhal number. The vortex flowmeter performance is also measured under disturbed flow conditions created by using gate valve and bends. These results are significant because they provide an optimum bluff body shape and blockage, and also present the performance of vortex flow meter under disturbed flow conditions which is rather seldom reported in the literature.     

半转翼的Weis-Fogh效应及推力的仿真研究

针对仿生飞行研究中具有重要应用前景的新型动力翼—半转翼的推力计算问题,提出了一种半转翼模型,导出了该模型参数的计算方法;基于XFLOW建立了两个半转翼CFD模型,即无固壁和有固壁半转翼模型,通过选择合理的流场计算区域和边界条件,采用湍流计算模型和刚性翼运动模型,结合半转翼实验模型参数和运动参数对半转翼流场速度、压力分布及推力进行了数值计算,获得了Weis-Fogh效应对半转翼运动流场特性和半转翼推力的影响规律,并与一个运动周期的实验推力进行了分析比较。研究结果表明:有固壁的半转翼流场中速度分布始终受到"急张"和"相拍"的影响,可大大提高半转翼的推力;由半转翼-固壁模型获得的推力计算曲线能真实反映半转翼推力的变化规律,这对计算不同参数的半转翼-固壁模型的推力具有参考价值。     

建模/仿真资源的网格化及其开发工具

为解决已有仿真资源在广域网上重用的问题，针对建模／仿真资源的特点对其网格化进行结构划分，提出了仿真资源网格化三层结构框架，以构建通用的建模仿真资源网格化支撑环境。该三层结构包括模型层、网格服务封装层和网格服务应用层。根据三层结构的特点，针对核心的网格服务封装层，开发了网格服务自动部署开发工具，实现服务封装的自动化，对仿真资源网格化三层结构的实现提供支持，从而达到了重用已有仿真资源、提高仿真资源网格化开发效率的目的。最后，介绍了利用三层结构和自动部署开发工具实现的仿真模型网格化应用实例。     

Numerical simulation of wind resonance of a circular profile by means of the vortex element method

The problem regarding the numerical simulation of a circular profile motion in a liquid flow has been studied. To calculate the flow and the aerodynamic loads acting on the profile, the vortex element method is used. The phenomenon of wind resonance has been examined. The investigation has revealed the range of self-frequencies of the circular profile fixed elastically, under which the periodical aerodynamic forces caused by Karman vortexes descend and initiate the resonance aeroelastic oscillations of the profile.     

斜截半椭圆柱面涡发生器在管道中的传热数值模拟研究

管内设置一种斜截半椭圆柱面涡发生器,利用计算软件F luent进行数值模拟研究,研究以烟气为加热介质,冷空气为冷却介质的换热方式在不同Re数下不同攻角和倾角的传热及阻力特性,并与光管进行了对比。结果表明:斜截半椭圆柱面涡发生器能明显提高换热性能,在所研究的纵向涡发生器中,攻角为60°,倾角为15°时,涡发生器强化传热综合效果最佳。     

Numerical solutions of flow past a circular cylinder at Reynolds numbers up to 160

Flow past a circular cylinder at Reynolds numbers up to 160 is simulated using high resolution calculations. Flow quantities at the cylinder surface are obtained and compared with those from the existing experimental and numerical studies. The present study reports the detailed information of flow quantities on the cylinder surface at low Reynolds numbers.     

轴向间隙引气对双级轴流式压气机性能及流场影响的数值研究

采用数值模拟的方法,研究了引气对某双级轴流压气机气动性能的影响。数值计算所获得实壁机匣总性能与试验结果符合良好,结果表明,在靠近第二级转子前缘处的机匣引气能够有效地提高压气机的失速裕度的同时,对压气机的压比和效率影响较小,分析了引气对压气机顶部区域流场结构的影响。     

Numerical simulation of fluid-structure interaction of a moving flexible foil

The hybrid Cartesian/immersed boundary method is applied to fluid-structure interaction of a moving flexible foil. A new algorithm is suggested to classify immersed boundary nodes based on edges crossing a boundary. Velocity vectors are reconstructed at the immersed boundary nodes by using the interpolation along a local normal line to the boundary. For eliminating pressure reconstruction, the hybrid staggered/non-staggered grid method is adapted. The deformation of an elastic body is modeled based on dynamic thin-plate theory. To validate the developed code first, free rotation of a foil in a channel flow is simulated and the computed angular motion is compared with other computational results. The code is then applied to the fluid-structure interaction of a moving flexible foil which undergoes large deformation due to the fluid loading caused by horizontal sinusoidal motion. It has been shown that the moving flexible foil can generate much larger vertical force than the corresponding rigid foil and the vertical force can be attributed to the downward fluid jet due to the alternating tail deflection. This paper was recommended for publication in revised form by Associate Editor Haecheon Choi Sangmook Shin received his B.S. and M.S. degrees in Naval Architecture from Seoul National University, Korea in 1989 and 1991, respectively. He received his Ph.D. degree in Aerospace Engineering from Virginia Tech, USA in 2001. He is currently an Assistant Professor at Department of Naval Architecture and Marine Systems Engineering at Pukyong National University in Busan, Korea. His research interests include fluid-structure interaction, unstructured grid method, internal wave, and two-phase flow. Hyoung Tae Kim received the B.S. and M.S. degrees in Naval Architecture from Seoul National University in 1979 and 1981, respectively and the Ph.D. degree in Mechanical Engineering from University of Iowa, U.S.A. in 1989. Dr. Kim is currently a Professor at the Department of Naval Architecture & Ocean Engineering at Chungnam National University, Korea. His research interests are in the area of Ship Hydrodynamics, CFD calculations of turbulent flows around ships and propellers, and human-powered and solar boat design.