通气超空泡稳定性分析的一种数值算法

根据Logvinovich独立膨胀原理发展了一种用于计算非定常通气超空泡形态的计算方法,并运用该方法对通气超空泡形态稳定性进行了数值仿真研究. 研究表明:Semenenko提出的稳定性判据可以有效判定通气超空泡形态稳定性,当超空泡处于判据的稳定区域时,超空泡表面形成的扰动波在扰动停止一段时间后消失,超空泡恢复到初始形态;当超空泡处于判据的不稳定区域时,超空泡发生自激振荡,超空泡表面形成的扰动波振幅逐渐增大,导致超空泡形态与内部压力发生周期性或准周期性振荡.      

STW型生态土壤稳定剂改良工程粘性土胀缩性试验研究

根据Logvinovich独立膨胀原理发展了一种用于计算非定常通气超空泡 形态的计算方法,并运用该方法对通气超空泡形态稳定性进行了数值仿真研究. 研究表明： Semenenko提出的稳定性判据可以有效判定通气超空泡形态稳定性,当超空泡处于判据的稳 定区域时,超空泡表面形成的扰动波在扰动停止一段时间后消失,超空泡恢复到初始形态; 当超空泡处于判据的不稳定区域时,超空泡发生自激振荡,超空泡表面形成的扰动波振幅逐 渐增大,导致超空泡形态与内部压力发生周期性或准周期性振荡.     

水下爆炸近壁面流场局部空化形成机理

为深入认识水下爆炸近壁面流场局部空化的形成机理，采用自行研制的转镜式分幅相机，获得了炸药水下爆炸近壁面流场局部空化效应的光学图像，结合数值模拟和Taylor平面波理论、空泡动力学理论，分析了近壁面空化效应的形成过程。结果表明：界面反射的稀疏波作用和水中空化核的膨胀发展是水下爆炸近壁面流场空化效应形成的原因；外界流场压力对空泡初期膨胀运动影响较小，对空泡后期运动行为影响较大；低压环境下不同尺度空泡的运动行为存在较大差异，小尺度空泡（半径小于10μm）在低压环境下处于快速膨胀、溃灭状态，对流场空化影响较小；大尺度空泡（半径大于10μm）可失去稳定性，半径持续增大，对流场空化区的形成影响较大；水中不同尺寸空泡空间分布的随机性可导致空化区成长过程中呈现非规则形状。     

水下航行体通气超空泡形态实验研究

在水洞中对航行体模型的通气超空泡形态及其影响因素进行了系列实验研究。在低速的情况下通过向空化器下游通入空气生成了超空泡。通过改变水洞速度、压力，通气参数，模型外形和状态产生了多种超空泡外形并研究了超空泡外形与空化器、空化数和通气参数之间的关系以及影响超空泡形状的因素，得出了有益的结论。对于下一步的研究工作具有指导意义，对于航行体超空泡外形控制技术的研究具有重要参考价值。     

超空泡形态及其流动特性的数值模拟

对圆盘空化器分别采用CFD、"1/3法则"和空泡截面独立扩展原理三种不同方法数值模拟了水下航行体定常自然超空泡外形及其流动特性。应用CFD方法基于粘性多相流的空泡捕捉法,采用六面体网格,选择Singhal空化模型和SST湍流模式,数值求解均质超空泡流场RANS方程。研究表明:泡形态时变特性是一种行之有效的工程估算方法,应用空泡截面独立扩展原理其计算结果与CFD方法吻合较好,说明了CFD方法用于超空泡流动仿真计算的可行性和独立性原理快速估算超空泡形态的准确性;同时超空泡外形主要与头部空化器有关,空泡长度会由于航行体本身存在变长;可优先选择空泡截面独立扩展原理对水下航行体超空泡外形进行快速估算。     

超空泡航行体转弯运动流体动力特性的数值研究

基于有限体积法,采用两流体多相流模型和SST(Shear Stress Transport)湍流模型,建立了用于求解超空泡航行体转弯运动过程中的三维数值模型,研究了转弯运动条件下通气空泡的形态特征及超空泡航行体的流体动力特性。计算结果表明:在转弯运动过程中空泡产生弯曲变形,空泡轴线与航行体运动轨道基本重合;由于空泡的弯曲变形航行体两侧表面呈现非对称沾湿,利用空化器横向偏转能够避免沾湿区的出现,而且对航行体水平面流体动力有良好的控制作用。     

超空泡横截面独立膨胀原理解析及其应用

应用能量守恒定律阐释了空泡横截面独立膨胀原理,推导了空泡横截面面积与水中运动物体的相对速度及空化数之间的关系式,对Logvinovich给出的公式作了进一步的完善和扩充,并在此基础上研究了若干种非定常条件下,圆盘后部有限轴对称超空泡长度和形态的非定常变化过程,通过数值算例说明了方法的可行性。本文结论可为水中超空泡航行体的设计提供理论参考,对相关数值计算有重要理论指导意义。     

航行体垂直出水载荷与空泡溃灭机理分析

针对航行体水下垂直发射出水载荷机理问题, 首先开展了典型工况全过程的数值 模拟, 得到了航行 体肩、尾空泡及表面压力的演化过程, 并与试验结果进行了对比验证. 在此基础上揭示了航 行体肩部空泡溃灭的过程和机制, 进而提出了出水溃灭压力的物理模型, 探索了空泡厚度、 水层厚度、声速等重要参数的影响, 讨论了试验溃灭压力相似律等相关问题.     

超空泡射弹尾拍分析与计算

对超空泡射弹进行运动学和动力学分析并数学建模,求解耦合非线性微分方程组,得到水下高速超空泡射弹运动特性。数值模拟结果表明,高速超空泡射弹在航行过程中,由于弹体头部和尾部的阻力作用,水平速度随时间迅速衰减。并且射弹的角速度呈周期性往复变化,即尾拍现象。同时由于空泡尺寸的减小导致尾拍幅度逐渐变小。射弹转动惯量越小,角速度变化幅度越平稳,相同时间内尾拍次数减少。发射深度或发射速度越大,尾拍幅度衰减越快。较大的初始角速度也会使射弹角速度很快衰减。     

环形槽对通气空泡融合的促进作用分析

航行体出水过程中肩部的自然空化将影响航行体的载荷分布及出水姿态,工程上常采用肩部开孔通气的方式改善航行体表面的力学环境, 进而解决此类问题.本文针对水下航行体通气空泡周向融合效果不理想问题, 基于有限体积法,采用VOF (volume of fluid)多相流模型和动态铺层的动网格技术,数值研究了排气孔下游增加小尺度环形凹槽促进空泡融合的作用机制,以及不同发展阶段、不同工况下环形凹槽对空泡融合的促进作用. 结果表明,凹槽可以有效改善通气空泡的融合效果.运动坐标系下来流经过环形凹槽时因为流动膨胀发生了边界层的流动分离,其诱导产生的卷吸作用一方面迟滞了空泡的轴向发展,促进空泡产生周向尺寸更大的剪切涡并沿周向膨胀发展,另一方面将部分通气气体吸入环形凹槽,吸入槽内的气体通过挤压破碎实现了周向融合,且槽内融合气泡溢出下泄促进融合边界上移. 此外,凹槽可以通过改善空泡内部的流动状态,使空泡的形态和内部压力在不同工况下都更加稳定.      

基于双向流固耦合的超空泡射弹入水研究

超空泡射弹通过超空泡减阻技术在水下高速长距离航行, 是对抗水下近距离威胁的有效手段. 为了扩大防御范围、增加杀伤力, 超空泡射弹具有很高的发射速度. 高速超空泡射弹在入水时中受到极大的冲击载荷, 发生显著的结构变形, 结构变形与流场之间存在相互影响和作用, 常规的基于刚体假设的仿真研究方法不再适用. 为了研究高速超空泡射弹入水过程中的结构变形及其对流体动力特性的影响, 通过耦合流体力学求解器和结构动力学求解器, 建立了射弹高速入水双向流固耦合仿真模型, 并通过与文献中的试验结果进行对比验证了该模型空泡形态计算方法和耦合方法的准确性. 使用双向流固耦合的方法对高速射弹在不同初始攻角入水过程中的超空泡流动特性及结构变形特性进行了数值模拟研究, 通过对比流固耦合模型与刚体模型的计算结果, 得到了超空泡射弹的结构弯曲变形对流体动力载荷的影响. 研究结果表明: 高速射弹入水过程中流固耦合效应对超空泡流型及流体动力载荷的计算结果有显著影响; 本文所研究的射弹在考虑流固耦合效应, 带攻角垂直入水两倍弹长的范围内, 超空泡射弹的流体动力载荷与弯曲变形之间形成正反馈; 高速超空泡射弹在入水过程中受到的流体动力载荷及弹体应力应变随入水初始攻角的增加显著增大, 研究对象在初速1400m/s的条件下入水时, 当初始攻角不超过2°时不存在结构安全性问题.      

可压缩旋转气体中超空化射流的热稳定性

液体射流热稳定性研究是对射流稳定性问题的更深层次的探讨,可以进一步加深对液体射流分裂与雾化机理的认识,具有重要的学术意义和工程应用价值. 基于射流稳定性理论,在同时考虑射流周围气体旋转、射流和周围气体可压缩性以及射流液体中含空化气泡的条件下,建立了描述可压缩旋转气体中超空化射流热稳定性的数学模型,并对数学模型及其求解方法进行了验证分析;在此基础上,分析了液体射流表面与周围气体间温差及射流内部温度梯度同时作用下对射流稳定性的影响;并进一步探讨了超空化射流的热稳定性. 结果表明,射流表面扰动波的最大扰动增长率、最不稳定频率以及最大扰动波数皆随气液温差的增大呈近似线性增大趋势;射流内部温度梯度的存在使得气液温差对射流的失稳作用更加显著;射流内部温度梯度会抑制超空化对射流稳定性的影响,但气液温差会在一定程度上促进超空化对射流的失稳作用.      

同轴旋转可压缩流动中液体射流稳定性

基于线性稳定性理论,建立了描述同轴旋转可压缩流动中超空化条件下液体射流稳定性的数学模型,并对数学模型及其求解方法进行了验证;在此基础上,对模型中考虑的射流及气体可压缩性、气体同轴旋转以及超空化等因素对射流稳定性的影响进行了分析. 分析结果表明,模型中考虑射流及气体的可压缩性后,与不考虑可压缩性相比,计算得到的射流稳定性明显变差,最小液滴直径减小,分裂液滴直径变化范围变宽,且小液滴数量增多. 气体的同轴旋转在轴对称与非轴对称扰动下对射流稳定性的影响完全相反;轴对称扰动时,气体旋转使射流稳定性增强,而非轴对称扰动时则正好相反;气体旋转有可能导致影响射流稳定性的扰动模式发生根本性变化. 超空化使射流稳定性变差;超空化程度较弱时,超空化使分裂液滴最小直径减小,分裂液滴直径变化范围增大;而超空化达到一定程度后,进一步提高超空化程度,分裂液滴最小直径几乎保持不变.     

Starting of an axisymmetric convergent-divergent nozzle in a hypersonic flow

The starting of an axisymmetric convergent-divergent nozzle, with the result that supersonic flow is formed within almost the entire channel, is modeled, as applied to the hypersonic aerodynamic setup of the Institute of Mechanics of Moscow State University. A successful starting is realized when the nozzle is thrown in a uniform supersonic air flow at a fairly high Mach number. The steady flow structure is studied. It is numerically shown that in the convergent section of the channel there arises an oblique shock wave whose interaction with the nozzle axis leads to the formation of a reflected shock and a curvilinear Mach disk with a region of unsteady subsonic flow in the vicinity of the throat. The mathematical model is based on the two-dimensional Euler equations for axisymmetric gas flows.     

一种三阶有限体积法及其在欠膨胀射流激波结构数值模拟中的应用

以喷管出口欠膨胀射流为研究对象,在Lagrange坐标系下建立欠膨胀射流二维积分形式的流动方程。通过在单元交接面处进行三阶ENO(essentially nonoscillatory)格式插值,构造得到一种适用于求解该方程的三阶ENO有限体积法。采用该格式对一维Sod激波管算例和喷管出口欠膨胀射流进行数值计算。计算结果表明,该方法具有高精度、基本无振荡的特点,能很好地捕捉包含激波、滑移线以及三波交点等复杂流场波系结构。计算得到的波系结构中马赫盘的位置与实验结果吻合很好,相对误差小于1.1%。     

Interaction of the vortex structures formed in parallel pulsed jets

The experimental investigation of the lateral interaction of the heads of pulsed jets and primary shock waves at various nozzle spacings and pressure ratio numbers is described. The various stages of formation of a composite pulsed jet issuing from a multinozzle block are classified and the flow development mechanisms are explored. It is shown for both a block and a single nozzle the shock wave travels with almost the same velocity, whereas the jet front formed at the exit from a single nozzle moves much more slowly than the jet front formed beyond a nozzle block. Long-lived lateral bursts of gas, whose dimensions are an order greater than those of the jet bursts, are detected. Their long period of existence considerably increases the stabilization time of the steady-state structure and parameters as compared with a single pulsed jet with the same flow rate.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 153–159, November–December, 1987.     

Investigation on the generation process of impact-driven high-speed liquid jets using a CFD technique

High-speed liquid jets have been applied to many fields of engineering, science and medicine. It is therefore of benefit to all these areas to investigate their characteristics by modern and inexpensive methods using a computational fluid dynamics (CFD) technique. Previously, high-speed liquid jets have been studied experimentally using a momentum exchange method, called the “impact driven method (IDM)”, by which the impact of a high-velocity projectile on the liquid package contained in the nozzle cavity produced the jet. The shock pulse reflections in the cavity caused by the impact then drove a multiple pulsed jet from the nozzle exit. In this study, a two-fluid simulation consisting of liquid and air can be successfully calculated by using a two-phase flow mixture model and a moving mesh for the projectile motion. The CFD results show good agreement to the results of previous experimental studies, both quantitatively and qualitatively. For the first time, the wave propagation within the liquid in the nozzle has been captured and analyzed, thereby demonstrating the dynamic characteristics of multiple pulsed high-speed liquid jets initiated by the IDM. This provides a breakthrough in the simulation of the supersonic injection of a liquid into air by using a well-known and user-friendly CFD software. It is useful fundamental knowledge for future studies of high-speed injection with applications in all its related fields.     

超空化条件下液体射流热稳定性研究

基于线性稳定性理论,建立了描述超空化条件下液体射流热稳定性的数学模型,并对数学模型及其求解方法进行了验证;在此基础上,对超空化条件下液体射流与周围气体间的温差对射流稳定性的影响进行了研究。研究结果表明,液体射流与周围气体间存在温差时,射流稳定性变差,扰动波波数范围拓宽,且拓宽的程度随温差的增加有明显加大的趋势;温度扰动对射流稳定性的影响与扰动模式关系不大;温度扰动会在一定程度上削弱超空化对射流稳定性的作用,并有可能完全抑制超空化对扰动波最大波数的作用,只有当超空化达到一定程度后,才能克服温度扰动的抑制作用,使扰动波最大波数变大。     

Jet interaction at supersonic cross flow conditions

The thrust produced by lateral jet systems has been successfully used for several years to control the flight trajectory, i.e., the maneuverability of spacecraft in the high atmosphere and in orbit. Recently this technology has also been applied to projectiles and rockets flying in the low atmosphere from sea level up to more than 10 km. At ISL, investigations have been performed with a 90 mm caliber full-scale projectile in order to study a special side jet controlling system at flight speeds of about 1500 m/s, i.e., Mach number at altitudes of 1.5 and 7.5 km. The High Energy ISL Shock Tunnel facility is used as a ground testing facility in which the flow around the projectile is studied at fully duplicated flight conditions. In the test facility the projectile is fixed inside the test chamber and the atmospheric air is set in motion flowing around the projectile test model. The air flow is generated in the ISL Shock Tunnel STB which is equipped for this purpose with a divergent square nozzle with an exit side length of 184 mm. A lateral gas jet is produced by combusting a solid propellant in a combustion chamber, placed inside the projectile. The powder gases are blown out laterally via a nozzle, creating a complex flow field by the interaction of the lateral jet with the external cross flow. Differential interferometry is used to visualize the behavior of the external flow field distorted by the lateral jet outflow. Numerical simulations have been performed based on steady state computations using the conservation equations of mass, momentum and energy. This was done to theoretically predict the development of the flow field around the projectile under the influence of the side jet. As final result the lateral force acting on the projectile is given as force and moment amplification factors, K_F and K_M respectively.Received: 7 May 2002, Accepted: 12 March 2003, Published online: 16 May 2003An abridged version of this paper was presented at the 23rd Int. Symposium on Shock Waves at Fort Worth, Texas, from July 22 to 27, 2001     

Interaction of a supersonic jet exhausting into vacuum with an obstacle

A study is made of the interaction between an axisymmetric supersonic jet exhausting into vacuum and an obstacle of a fairly complicated configuration and positioned relative to the nozzle in such a way that in the interaction region behind the detached shock wave there is a three-dimensional flow possessing a symmetry plane. The flow in the interaction region is described by the system of equations of motion of an inviscid perfect gas with boundary conditions on the shock wave (Rankine-Hugoniot relation) and on the surface of the obstacle (no-flow condition). The other boundaries of the region are the symmetry plane of the flow and an arbitrarily chosen surface in the supersonic part of the flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti Gaza, No. 1, pp. 156–161, January–February, 1981.