潜射导弹水下垂直自抛发射过程研究

研究了潜射导弹水下垂直自抛发射过程中的复杂多相流动问题。采用多相流mixture模型，考虑了流体的可压缩性、黏性、重力作用、气水掺混效应和能量交换等各项因素。应有限体积法（FVM）和Simple算法，求解气水两相混合介质的RANS方程和standard k-ε湍流模式。运用自编UDF模块和动网格技术，实现了导弹出筒过程中弹体运动与气水流场的耦合求解。计算结果揭示了潜射导弹水下垂直自抛发射过程中发动机喷管和发射管内复杂多相流动的演化、流场结构和流体动力特性。     

潜射导弹出筒过程的三维非定常数值模拟研究

潜射导弹出筒过程的研究对其水弹道以及水下动载荷的计算具有重要的意义。本文采用多相流模型和动网格技术,求解非定常雷诺平均NS方程,对考虑潜艇平动影响的导弹冷弹射出筒过程进行了三维非定常数值模拟。三维数值模拟体现出筒口效应、发射气团现象等经典实验现象与实验符合较好,说明本文方法能够有效地揭示导弹出筒过程中多相流体间的相互作用以及相应的流体动力特性,通过分析这些现象中导弹所受冲击的形成机理,为工程应用提供有意义的参考。     

水下航行体垂直发射尾部空泡形态与压力预示方法研究

水下航行体垂直发射尾部空泡形态与压力准确预示是航行体轴向速度设计的重要依据。该文基于对尾空泡形态发展演变的基本规律的认识,结合空泡独立膨胀原理和Rayleigh-Plesset方程,建立了尾空泡非定常发展数学模型,形成了尾空泡形态和压力的理论预示方法,并通过与试验数据的比对,验证了方法的合理性和可用性。此外,还研究了航行体出筒速度、阻力系数、尾空泡初始压力和燃气指数等影响要素对尾空泡压力和形态的影响。     

考虑横向流影响的水下齐射载荷特性研究

该文围绕多细长体水下垂直齐射载荷特性,采用VOF多相流模型、k-ε湍流模型和分层嵌套动网格等仿真技术,结合自定义函数(User-Defined Function, UDF)编程模拟的不同水深环境,并考虑艇速、筒口结构形式、筒盖和均压气体等对水下齐射过程流场状态的影响,建立了考虑横向流影响的水下齐射三维非定常多相流场仿真模型,获取了筒口流场状态、相邻位置压强载荷及海水倒灌情况等。仿真结果表明,在一定齐射间隔条件下,前发发射后筒口气泡发展及海水倒灌过程会对后发发射产生一定影响;横向流除作用于弹体产生横向载荷外,也对弹体离筒后的筒口气泡发展演变有着较大影响。该研究方法和结论可为水下齐射发射方案论证及齐射安全性分析提供相关指导。     

通气超空泡航行体后体纵摆运动的数值模拟

利用Fluent 6.3对带圆盘空化器的高速水下航行体的通气超空泡流动进行了三维、非定常的数值模拟,通过在FLUENT软件中加入UDF自定义函数的方式求解非惯性系下的N-S方程,分析了通气超空泡航行体水下纵摆运动过程中的超空泡流流动特征和力学特性。结果表明,三维轴对称超空泡水下航行体的压力场具有如下特点:(1)泡内压力低于外界同样水深处水流压力,(2)泡内压力与泡外压力连续变化,(3)泡内压力分布不均匀,泡内气体在压力差驱动下形成沿周向的二次流动;该二次流动是形成超空泡尾部涡管状泄气结构的重要因素。文中将仿真计算结果与空泡水洞试验进行了对比,验证了数值计算的有效性。     

细长体空泡流型试验研究

在水洞中对细长体通气附体空泡流型和控制途径进行了系列模型实验研究；获得了细长体通气附体空泡五种对称基本空泡流型与三种非对称基本空泡流型；在此基础上，从水下超空化超高速自主航行体的需求出发，提出了三种可用的空泡流型：非对称双空泡流型、尾部开式穿透非对称空泡流型和尾部半开式非对称空泡流型。并分析讨论了这三种空泡流型下航行体的重力平衡、运动控制与稳定性问题。同时，通过对有关参数的设计与控制，在水洞模型试验中实现了水下超空化超高速自主航行体的这三种空泡流型。     

利用球形气泡模型研究导弹水下点火瞬间的推力状况

本文利用由球形气泡假设所得到的简单数学模型研究了导弹在水下点火瞬间所受到的推力状况。计算结果显示由于水的惯性作用,导弹在水下点火瞬间所受到的推力将急剧增大,推力峰值随着喷管喉部截面积和膨胀面积比的增大而增大。而随着导弹发射深度的增大而减小,导弹所受到的推力在峰值后将出现低频波动。     

上海交通大学船舶及海洋工程流体力学研究室概况

上海交通大学船舶及海洋工程流体力学研究室主要研究领域包括船舶阻力、推进、适航性和操纵性,从七十年代初开始,海洋工程结构物的流体动力载荷及其运动性能也成为重点发展的研究领域之一。 研究室下设三个实验室,即船模拖曳试验池、空泡水筒和操纵模拟实验室。船模拖曳试验池建于1958年,其主尺度为长110米,宽6米,水深3米,可进行船舶及海洋工程结构物的流体动力性能试验研究。空泡水筒建于1978年,其技术特征为工作段直径0.6米、长2米、最大流速为每秒15米,可进行螺旋桨、水翼、舵等的空泡剥蚀、噪声及螺旋桨激振力的研究。参加国际船模试验池会议发起组织且作为实验室活动的一部份的各种比较性试验表明,试验结果具有高度准确性,各种设备及测试系统稳定而可靠。操纵模拟实验室有船舶运动模拟器、自航操纵船模和测量船舶及海洋工程结构物的流体动力系数的平面运动机构。     

用MAC方法计算平头物体垂直等速入水空泡

本文用MAC方法模拟平头物体垂直等速入水空泡发展的全过程,用有限差分法直接解N-S方程,用标记质点显示液面位置和空泡形状,不必先假定空泡形状,自由面上的运动学条件和动力学条件自然得到满足。数值计算给出了空泡发展的过程,包括分离、开空泡、深闭合和闭合后的射流,还给出了物面上的压力分布和阻力系数。     

喷管不同摆角对水下发射导弹受力的影响

论文研究了带摆喷管推力矢量控制系统的导弹水下垂直发射时,不同喷管摆角对三维水气流场的非定常发展变化过程及对导弹受力的影响。采用燃气泡物理模型,通过水气流场的耦合计算研究燃气与水的相互作用,运用欧拉-拉格朗日和时间步进的方法跟踪燃气泡自由面。以三维欧拉方程为控制方程对喷管和燃气泡内的三维气流场进行数值计算,根据燃气泡不断运动变化的交界面生成贴体动网格,在贴体坐标系下采用无波动、无自由参数、耗散的差分格式(NND差分格式)数值求解三维气流场。采用势流理论,以拉普拉斯方程为控制方程,利用三维Hess-Smith方法数值求解了导弹与燃气泡周围的三维水流场。给出了不同时刻泡形的变化,气流场内马赫数、压力的演变规律,导弹受力及力矩。通过多个工况的对比计算,研究了喷管摆角对导弹受力及水气流场的影响。     

Numerical analyses of ventilated cavitation over a 2-D NACA0015 hydrofoil using two turbulence modeling methods

The present paper studies the ventilated cavitation over a NACA0015 hydrofoil by numerical methods. The corresponding cavity evolutions are obtained at three ventilation rates by using the level set method. To depict the complicated turbulent flow structure, the filter-based density corrected model(FBDCM) and the modified partially-averaged Navier-Stokes(MPANS) model are applied in the present numerical analyses. It is indicated that the predicted results of the cavitation shedding dynamics by both turbulence models agree fairly well with the experimental data. It is also noted that the shedding frequency and the super cavity length predicted by the MPANS method are closer to the experiment data as compared to that predicted by the FBDCM model. The simulation results show that in the ventilated cavitation, the vapor cavity and the air cavity have the same shedding frequency. As the ventilated rate increases, the vapor cavity is depressed rapidly. The cavitation-vortex interaction in the ventilated cavitation is studied based on the vorticity transport equation(VTE) and the Lagrangian coherent structure(LCS). Those results demonstrate that the vortex dilatation and baroclinic torque terms are highly dependent on the evolution of the cavitation. In addition, from the LCSs and the tracer particles in the flow field, one may see the process from the attached cavity to the cloud cavity.     

THE WALL EFFECT ON VENTILATED CAVITATING FLOWS IN CLOSED CAVITATION TUNNELS

For ventilated cavitating flows in a closed water tunnel, the wall effect may exert an important influence on cavity shape and hydrodynamics, An isotropic mixture multiphase model was established to study the wall effect based on the RANS equations, coupled with a natural cavitation model and the RNG k-ε turbulent model. The governing equations were discretized using the finite volume method and solved by the Gauss-Seidel linear equation solver on the basis of a segregation algorithm. The algebraic multigrid approach was carried through to accelerate the convergence of solution. The steady ventilated cavitating flows in water tunnels of different diameter were simulated for a conceptual underwater vehicle model which had a disk cavitator. It is found that the choked cavitation number derived is close to the approximate solution of natural cavitating flow for a 3-D disk. The critical ventilation rate falls with decreasing diameter of the water tunnel. However, the cavity size and drag coeflicient are rising with the decrease in tunnel diameter for the same ventilation rate, and the cavity size will be much different in water tunnels of different diameter even for the same ventilated cavitation number.     

通气空泡重力效应研究

该文基于VOF方法和有限体积法,求解气水多相流动的RANS方程及标准湍流模式,研究了通气空泡的重力效应.结果表明模拟得到的绕圆盘通气空泡的重力效应与Buyvol的分类准则吻合,通过数值模拟复演了通气空泡的双涡管泄气模式;证实由于与尾空泡的相互作用,重力作用下绕航行体通气空泡在尾部附近出现下沉,航行体上的空泡截面呈现出"月牙"形;阻力随空化数而减小,并在空泡完全包裹住航行体前部锥段时出现突降.     

NUMERICAL SIMULATION OF VENTILATED CAVITATING FLOW AROUND A 2D FOIL

By using a pressure-based method and the finite volume method in the framework of the time dependent Reynolds-averaged Navier-Stokes equations, the authors studied the unsteady process of ventilated cavities generated forcing air through an orifice in a 2D hydrofoil without natural cavitation physically. The computation was carried out with the Volume Of Fluid （VOF） technique to track the gas-liquid two-phase interface. The results of simulation indicate that the ventilation rate is an important parameter in determining the morphology of cavity. There exists a critical value to convert sheet cavity into supereavity. A high ventilation rate can induce a two phase interface fluctuation and enable the ventilated eavitating flow to present a characteristic of periodicity.     

NUMERICAL SIMULATION OF ARTIFICIAL VENTILATED CAVITY

1. INTRODUCTION The cavitation phenomenon[1,2] has already been paid high attention as a primary characteristic in the process of underwater body’s manufacture and exploitation. For a long time, the purpose of cavitation research is to prevent the occurr…     

NUMERICAL INVESTIGATION OF THE VENTILATED CAVITATING FLOW AROUND AN UNDER-WATER VEHICLE BASED ON A THREE-COMPONENT CAVITATION MODEL

Based on the Reynolds-Averaged Navier-Stokes equations and mass transfer model,an approach,where a three-component cavitation model is proposed,is presented to simulate ventilated cavitating flow as well as natural cavitation.In the proposed cavitation model,the initial content of nucleus in the local flow field is updated instantaneously,and is coupled with the Rayleigh-Plesset equation to capture the cavity development.The proposed model is applied to simulate the cavitating flow around an under-water veh...     

绕二维对称水翼的通气空泡流数值研究

本文通过有限体积离散方法求解Reynolds平均Navler—Stokes方程，采用VOF法追踪气一液两相交界面。研究了在高压低速来流，即本质上不发生自然空化的条件下，绕二维对称水翼的非定常通气空泡流动。分析了物理参数——通气方向角和攻角，对通气空泡外形、稳定性及水动力参数的影响。计算结果表明：在通气空泡的形成过程中，通气方向角存在着一个临界值，使得空泡形态由片状空泡过渡到超空泡；特定的参数组合将会诱发空泡表面出现波动现象。而且，当攻角做周期性变化时，水动力参数的变化也随之满足周期性规律，且出现阶段性振荡。     

Hydrodynamics and modeling of a ventilated supercavitating body in transition phase

Compared to other underwater vehicles, supercavitating vehicles can attain a high speed because they eliminate drag by creating a large cavity, thus establishing the so-called "supercavitating condition." Such a cavity is difficult to develop under normal conditions, hence, ventilation is used to attain the supercavitating condition in the initial phase of flight. In this paper, we focus on the hydrodynamic characteristics of a ventilated supercavitating vehicle. First, dynamic modeling of the supercavitating vehicle is performed to calculate the hydrodynamic force/moment acting on the vehicle for a given size of cavity. We then define the relationship between the ventilation rate and the cavitation number based on an air entrainment model of the ventilated cavity. Numerical simulations were performed to analyze the physical feasibility and characteristics of the modeling. The results show that the cavity length/radius increases with the ventilation rate, proving that ventilation can be used to attain the supercavitating condition.     

EXPERIMENTAL RESEARCH ON THE SHAPE CHARACTERS OF NATURAL AND VENTILATED SUPERCAVITATION

A series of projectile and water-tunnel experiments were conducted to investigate the shape characters of natural and ventilated supercavitation. It was found that the shape and dimensions of both the natural supercavitation and the ventilated supercavitation are similar through the comparison of them when the cavitation number is small and equal, and the contour of both the natural supercavitation and the ventilated supercavitation can be calculated effectively with the Savchenko formula. The gravity effect can induce the asymmetry of ventilated supercavitation, and the asymmetry is more apparent as the Froude number is smaller. The empirical formula for calculating the axial deformation of ventilated supercavitation was corrected and expanded based on experiment data. The evolution rules of both the natural supercavitation and the ventilated supercavitation were described, and the vortex frequency of natural cavitation was obtained. In addition, the hysteretic aspect was observed between the development and the fall process of ventilated cavitation.     

PREDICTION OF UNSTEADY CAVITATION OF PROPELLER USING SURFACE-PANEL METHOD

This paper has predicted the range and volume of unsteady sheet cavitation of a propeller by using the surface panel method. The linearization in cavity thickness is adopted to reduce the computing time and storage space. The iteration scheme between chordwise strips has been used because the range and volume of cavitation are both unknown. The propeller cavitation range determined by the calculation method presented in this paper agrees with the observation results of cavity image at cavitation tunnel very well, and this proves the practicability of the method.