k-ε双方程湍流模型对制退机内流场计算的适用性分析

为研究不同双方程湍流模型对制退机内复杂流场计算的适用性,以某火炮制退机为研究对象,建立了实际结构下的三维计算模型,利用动网格与滑移网格技术,实现了火炮实际后坐速度下的制退机内部三维运动流场的数值计算。分别采用标准k-ε模型、RNGk-ε模型和Realizable k-ε模型计算制退机内部各腔室压力,与实验曲线对比,结果表明,应用标准k-ε模型对后坐冲击过程的制退机内部压力计算的误差最小,与实验结果吻合最好。     

k-ε双方程湍流模型对制退机内流场计算的适用性分析

为研究不同双方程湍流模型对制退机内复杂流场计算的适用性,以某火炮制堪机为研究对象,建立了实际结构下的三维计算模型,利用动网格与滑移网格技术.实现了火炮实际后坐速度下的制退机内部三维运动流场的数值计算.分别采用标准k-ε模型、RNGk-ε模型和Realizablek-ε模型计算制退机内部各腔室压力,与实验曲线对比,结果表...     

带制退器膛口流场的三维数值模拟

利用三维任意坐标 系下Euler方程组和LU分解的数值方法模拟了不带膛口装置的某步枪膛口流场，计算结果与 实验结果比较吻合. 对某口径火炮带有制退器的膛口流场进行了数值模拟，其结果反映了制 退器内外流场的主要特征和冲击波波系之间的相互作用，在数值模拟的基础上分析 了3排侧 孔对制退器性能的影响. 本文提供了有关膛口流场的详细数据，将对制退器总体性能研究有 重要的参考意义.     

非结构混合网格高超声速绕流与磁场干扰数值模拟

对均匀磁场干扰下的二维钝头体无粘高超声速流场进行了基于非结构混合网格的数值模拟.受磁流体力学方程组高度非线性的影响及考虑到数值模拟格式的精度,目前在此类流场的数值模拟中大多使用结构网格及有限差分方法,因而在三维复杂外形及复杂流场方面的研究受到限制.本文主要探索使用非结构网格(含混合网格)技术时的数值模拟方法.控制方程为耦合了Maxwell方程及无粘流体力学方程的磁流体力学方程组,数值离散格式采用Jameson有限体积格心格式,5步Runge-Kutta显式时间推进.计算模型为二维钝头体,初始磁场均匀分布.对不同磁感应强度影响下的高超声速流场进行了数值模拟,并与有限的资料进行了对比,得到了较符合的结果.     

侧向多喷口干扰复杂流动数值模拟研究

采用具有高分辨率的NND格式，通过数值求解N-S方程对典型外形多喷口侧向喷流 复杂干扰流动进行了数值模拟. 为了提高计算效率，采用了LU-SGS隐式算法. 采用分块对接 网格技术，生成高质量的贴体计算网格，精确模拟喷口截面. 对比分析了不同计算格式、限 制器形式、网格拓扑及流动形态(层流与湍流)对喷流干扰流场结构和压力分布特性的影响， 研究和分析了喷口附近流场的涡系结构、波系结构和喷流干扰引起的气动力特性. 在上述研 究的基础上，针对典型飞行器外形的侧向喷流干扰特性进行了详细的数值模拟，得到了喷口 参数(喷口位置、数目等)及来流条件对喷流干扰流场结构、气动力特性的影响规律，并对 其流动机理进行了相应的分析. 研究表明，发展的针对多喷口侧喷干扰的数值计算方法 是成功的，可以应用于飞行器侧向喷流干扰的流场结构分析及气动力特性数值预测.     

超声速多喷流干扰流场特性研究

研究了旋成体上超声速来流与超声速横向多喷流相撞产生的层流干扰流场特性. 数 值方法针对三维可压缩Navier-Stokes方程按二阶精度Roe格式进行离散，采用基于多区对 接网格技术的有限体积法. 数值模拟结果描述了多喷流干扰流场的空间结构以及激波/边界层 干扰引起的分离范围，探讨了沿流向等间距排列的喷口个数对表面和空间流场结构以及压力 分布的影响规律. 结果表明，第一喷口对多喷流干扰流场主要结构和喷口上游表面分离范围 起主导作用. 其中三喷流流场数值模拟的对称面激波结构与实验纹影结果进行对比，符合较 好.     

带制退器的膛口射流噪声数值模拟与实验研究

为了研究膛口装置对膛口噪声气动特性的影响，对带膛口制退器的某小口径武器的膛口射流噪声进行了数值模拟和实验研究。采用计算流体力学CFD (computational fluid dynamics)-计算气动声学CAA (computational aeroacoustics)耦合算法对膛口噪声进行数值模拟，即对膛口流场进行瞬态CFD模拟，获取流场数据，然后利用所得到的结果采用声学方程模拟声源信息求解声场。基于数值模拟结果，分析了膛口流场变化及噪声的指向性分布，并与实验结果进行了对比。研究表明:膛口制退器的安装改变了膛口流场结构，影响了膛口射流噪声的指向性分布。计算结果与实验结果的误差小于9%，验证了该计算方法的可行性。研究结果可为膛口射流噪声的预测及膛口制退器的设计提供一定的参考。     

高速流场气动光学RANS/DSMC混合数值模拟算法研究

提出了适用于高速流场气动光学数值模拟的RANS/DSMC混合算法.通过RANS对全局时均流场进行数值模拟,再对其中局部流场的脉动量采用DSMC进行数值模拟,以Maxwellian速度分布实现RANS宏观量信息向DSMC微观量信息的传递.采用超声速环境下尖劈模型对该混合算法进行校验,对比试验结果论证了算法的正确性.在计算...     

长江三峡巴东县城区三道沟滑坡成因研究

构造了三维混合层流场用离散涡丝描述的计算模型并进行了数值模拟．给出了流场的涡结构以及不同剪切率、不同扰劝强度下涡结构的特征，得到了流场中的平均速度、动量厚度．由计算被动粒子显示了流场螺旋涡结构的图像．做了相应的流动显示实验研究，所得结果与计算结果非常相近．本研究为了解该流场并由此进行流场控制提供了依据．     

用基于M-SST模型的DES数值模拟喷流流场

脱体涡数值模拟方法(dettached eddy simulation,DES)是把雷诺平均Navier-Stokes方程(RANS)方法及大涡模拟方法(LES)结合起来模拟有脱体涡的湍流流场的数值模拟方法,其主要思想是在物面附近解雷诺平均Navier-Stokes方程、在其他区域采用Smagorinski大涡模拟方法。本文在剪切应力传输(SST)湍流模型的基础上用DES及混合非结构网格数值模拟具有横向喷流的湍流流场,算法采用Osher逆风格式,利用该套程序(包括网格生成及算法),对导弹在不同马赫数下的喷流流场进行了数值模拟,并与同时开展的实验研究的结果进行了对比,结果表明用该方法处理这类问题是较准确的。     

磁流体特性对磁流变火炮后坐阻尼器性能的影响

针对火炮后坐磁流变阻尼器的特点,以某单管25 mm火炮实验用磁流变阻尼器为研究对象,基于Herschel-Bulkley本构模型,建立了该炮磁流变后坐阻尼器的轴对称一维层流模型,获得了不同磁场作用下阻尼力随活塞速度的变化规律。运用火炮的后坐运动方程,计算了不同磁流体特性指数下,火炮的后坐位移和后坐速度。计算结果表明,磁流体特性指数的变化对磁流变后坐阻尼器的性能影响显著。     

考虑活塞回复的侧向后喷武器两相流数值模拟

为研究活塞回复运动对火药燃气流动的影响,基于两相流理论对活塞控制侧向后喷武器的发射过程进行了数值模拟研究。考虑控制侧向后喷通道开闭的活塞-弹簧系统的往复运动,建立了结合膛内气固两相流、活塞腔内流固耦合和侧向排气管内气体瞬态流动的武器发射过程数学模型,并将数值模拟结果与相关文献进行了比较验证。得到了该武器发射过程中膛内流场分布与稀疏波传播特性,并与普通武器的膛内流场进行了对比分析。进一步研究了活塞回复运动对火药燃气流动和减后坐效率的影响。结果表明:相对于不考虑活塞的回复运动,在弹丸初速都降低1.52%的情况下,因为活塞回复关闭后喷通道,其减后坐效率由38.86%下降到32.88%,说明在此类武器研究中,不可忽视活塞回复运动。     

Effect of vent opening area and arrangement on gas flow field as gas propelled cylinder exits a flow tube

The effects of auxiliary flow tube vent opening area and arrangement on the gas flow field as a gas propelled cylinder exits a flow tube were studied numerically. Configurations with a single opening of increasing size and multiple opening arrangements with equivalent opening area were considered for comparison to a baseline no-opening system. The openings are positioned near the end of the flow tube. The intended use of the openings is to reduce the pressures of the gases escaping to the surroundings and thus to reduce the intensity and size of the gas expansion zone in the surroundings. The results indicated that increasing the opening flow area decreased the pressure at the axial end of the flow tube and the radial extent of the end of flow tube exit plume. However, the radially directed flow streams leaving through the side vent openings could increase the overall radial spread of the gas expansion into the surroundings. The single opening arrangement produced as much as a 95% decrease in the pressure at the end of the flow tube and a 37% decrease in the recoil force at a given time with about 95% of the exiting flow leaving through the opening. For the parameters considered, the multiple opening arrangement produced up to a 93% decrease in the pressure at the end of the flow tube and a 90% decrease in the recoil force at a given time with about 93% of the exiting flow leaving through the openings. The results showed larger single openings to be more effective at reducing end of flow tube pressure, while the multiple openings to be more conducive to a reduced recoil force.     

炮口冲击式火炮后坐模拟试验的数值分析

为了获得炮口冲击试验装置的冲击参数,保证火炮后坐模拟试验的精度和有效性,以某型地面火 炮为对象,基于MSC.ADAMS软件,开发了虚拟的火炮后坐模拟试验平台,实现了火炮动态后坐、复进过程 的动力学模拟,开展了冲击参数的均匀试验设计。通过试验与数值模拟结果的比较,验证了冲击参数组合的 合理性和模拟试验的有效性。     

Flow modulation of a planar free shear layer with large bubbles—direct numerical simulations

The flow of a planar free shear layer with cylindrical bubbles is simulated using a finite difference/front tracking scheme. This approach allows direct numerical simulation of the multiphase flow by wholly incorporating the local bubble flow field in conjunction with the large scale vortical structures of the liquid. The role of large bubbles in modifying low Reynolds number ( 250) shear flow structures is investigated, specifically for bubbles whose diameter approaches the scale of the largest liquid eddies. The results indicate that duration of eddy crossing is the main mechanism for flow modulation, which is typically characterized by decreased vortex coherency and size, modified fluctuation statistics and significant variations in pairing/merging phenomena. The comparison of fluctuating statistics and flow field visualization also allowed qualitative discrimination between the modulation of the non-linear eddy dynamics and fluctuations due simply to the random bubble induced perturbations.     

Elastic recovery of immiscible blends 1. Analysis after steady state shear flow

Due to the interfacial tension, immiscible blends can show an elastic recovery that is substantially larger than that of their pure components. Here it is attempted to relate the elastic recovery after steady shear flow to the underlying morphology. On the one hand, the predictions of the Palierne and the Doi-Ohta models are calculated for the flow conditions during recoil. On the other hand, systematic recoil experiments after steady state shearing have been performed on a model blend. As the component polymers hardly show any recoil under the stresses applied in these tests, the measured recovery can be attributed completely to the action of the interface. Comparison of the model predictions with the experimental results shows that the recoverable strain can be derived quantitatively from the linear Palierne theory. Although the droplet deformation remained limited during the preshear, the retardation time predicted by this model has to be multiplied by the aspect ratio of the droplet phase to the power 2/3 to describe the experiments. For conditions in which the material does not show an intrinsic length scale, particular scaling relations as derived from the Doi-Ohta theory are found to apply also to recoil. Received: 5 August 1998 Accepted: 17 November 1998     

流场非均匀性对非平面激波诱导的Richtmyer-Meshkov不稳定性影响的数值研究

基于Navier-Stokes方程组，采用可压缩多介质黏性流动和湍流大涡模拟程序MVFT (multi-viscous-flow and turbulence)，模拟了均匀流场与初始密度呈现高斯函数分布的非均匀流场中马赫数为1.25的非平面激波加载初始扰动air/SF₆界面的Richtmyer-Meshkov (RM)不稳定性现象。数值模拟结果表明，初始流场非均匀性将会影响非平面激波诱导的RM不稳定性演化过程。反射激波加载前，非平面激波导致的界面扰动振幅随着流场非均匀性增强而增大；反射激波加载后，非均匀流场与均匀流场条件下的界面扰动振幅差异有所减小。进一步，定量分析流场中环量分布及脉动速度统计量揭示了前述规律的原因。此外，还与平面激波诱导的RM不稳定性进行了简单对比，发现由于非平面激波波阵面区域的涡量与激波冲击界面时产生的涡量的共同作用，使得非平面激波与平面激波诱导的界面失稳过程存在差异。     

Mechanism of transition in a hypersonic sharp cone boundary layer with zero angle of attack

Firstly, the steady laminar flow field of a hypersonic sharp cone boundary layer with zero angle of attack was computed.Then,two groups of finite amplitude T-S wave disturbances were introduced at the entrance of the computational field,and the spatial mode transition process was studied by direct numerical simulation (DNS) method. The mechanism of the transition process was analyzed.It was found that the change of the stability characteristics of the mean flow profile was the key issue.Furthermore,the characteristics of evolution for the disturbances of different modes in the hypersonic sharp cone boundary layer were discussed.     

Mechanism of drag reduction by spanwise oscillating Lorentz force in turbulent channel flow

Numerical simulations and experimental research are both carried out to investigate the controlled effect of spanwise oscillating Lorentz force on a turbulent channel flow. The variations of the streaks and the skin friction drag are obtained through the PIV system and the drag measurement system, respectively. The flow field in the near-wall region is shown through direct numerical simulations utilizing spectral method. The experimental results are consistent with the numerical simulation results qualitatively, and both the results indicate that the streaks are tilted into the spanwise direction and the drag reduction utilizing spanwise oscillating Lorentz forces can be realized. The numerical simulation results reveal more detail of the drag reduction mechanism which can be explained, since the spanwise vorticity generated from the interaction between the induced Stokes layer and intrinsic turbulent flow in the near-wall region can make the longitudinal vortices tilt and oscillate, and leads to turbulence suppression and drag reduction.     

油水重力分离实验模拟系统的研制

所研制的油水重力分离实验模拟系统，由介质循环、乳化液制备、激光片光源、图象采集及设备模型等部分组成，可对系统流量、介质物性、分散相含量、乳化状态、设备结构等多种因素进行实验模拟，从而能有效地将实际介质在工程设备中的流动与分离过程再现到实验室中．该系统与ＰＩＶ、停留时间分布等有关检测技术相配合，可对多种油田地面分离设备进行多工况、多参数的流动诊断分析，为揭示介质在设备中的流动与分离规律、研究设备工作理论、优化设备结构等提供了重要手段．