水下航行体变深度发射出筒空泡数值研究

采用数值方法对水下航行体带均压气体出筒过程进行数值模拟,研究了发射筒内均压气体及发射深度对出筒空泡的影响。基于均值混合物多相流模型、气体状态方程、质量输运空泡模型和RNG k-ε湍流方程,并结合动网格技术,实现了水下航行体带均压气体出筒过程数值求解。通过对典型弹体模型从不同深度发射出筒过程进行数值研究,得到了出筒过程空泡形态特征和内部结构,对比分析不同发射深度空泡尾部闭合时气体弹性系数的变化规律,并与文献中理论分析结果进行了对比验证。研究结果表明:均压气体将跟随航行体运动在航行体表面形成通气空泡,气体的弹性系数将影响空泡内气体的脱落速度和空泡尾部闭合位置;相同的弹射速度下,发射深度越大,空泡尾部闭合的越早。     

水下射弹自然超空泡减阻特性的数值模拟

基于均质平衡多相流理论,采用Fluent6.3对水下射弹自然超空泡减阻特性进行了数值模拟。研究了空化数对水下射弹空泡闭合部位和阻力系数的影响,重点分析了水下射弹结构参数对自然超空泡减阻特性的影响,得到了空化器直径、模型长细比和不同尾部形状对水下射弹超空泡减阻特性影响的规律。数值模拟结果表明:随着空化器直径的增大,自然超空泡较易形成,但其减阻能力有所降低;随着长细比的增大,自然超空泡较难形成,但形成超空泡后,不同长细比模型的阻力系数基本一致;尾部形状只影响尾部空泡的发展过程,当尾部被空泡包裹后,模型的自然超空泡形态和阻力系数基本一致。     

超空泡航行体阻力系数的数值模拟研究

采用数值模拟的方法,仿真获得不同空泡形态下超空泡航行体的粘性阻力系数和压差阻力系数,利用这些系数,基于普通流线型航行体的阻力系数估算公式,进行重新拟合修正,形成超空泡航行体的阻力系数估算公式。将无空泡情况下的阻力系数估算公式代入自编的水下航行体弹道仿真软件,计算得到的超空泡航行体全沾湿状态下的水下弹道理论预报结果,与利用模型试验中的实测数据得到的弹道曲线一致性较好,说明数值模拟对超空泡航行体阻力系数的估算基本准确。     

潜射导弹空化特性水洞模型试验研究

潜射导弹水下弹道品质决定了发射过程的成败。发射速度提高形成的导弹附体空泡造成了流体动力的不确定性,增加了水下弹道设计的难度。针对潜射导弹水下航行的特点,采用通气空泡技术来模拟不同空化状态下航行的导弹,给出了空泡形态及其流体动力特性,分析了锥头锥角对空泡形态和流体动力特性的影响,得出了回射流效应及弹体自由攻角随锥角增大而增大的结论。借鉴超空泡武器外形理论,设计了增强弹道稳定性的截头锥头型,并通过试验验证了该头型弹体稳定性好的特点。试验结果可供潜射导弹水弹道设计人员参考。     

减震垫对导弹水下垂直发射横向振动的影响

在导弹的水下垂直发射过程中,减震垫的变形与导弹运动相互耦合,减震垫特性直接影响出筒过程中导弹的横向振动。根据动量和动量矩定理建立了导弹在出筒过程的动力学模型,分析了导弹在筒内横向运动的自由振动特性,得到了导弹在发射平台坐标系下的横向振动方程。在此基础上,研究了减震垫刚度、轴向尺寸和筒内分布对导弹横向振动频率、截面受力以及出筒姿态的影响。研究结果为导弹水下发射系统的结构设计及优化提供了理论基础与研究手段。     

潜载导弹水下发射出筒横向动力学特性研究

导弹在潜艇带速水下垂直发射出筒过程中涉及复杂的力学问题,弹体在出筒阶段受到适配器的约束,并受到其施加的横向支撑反力,使得出筒阶段弹体载荷水平较高。本文依据动量和动量矩定理建立了导弹水下垂直发射出筒过程动力学模型,并对艇速为1.5m/s、2.5m/s时两种横向支撑方式对导弹的出筒过程中的力学特性开展了仿真计算。结果表明：两种横向支撑方式下,适配器方式的出筒姿态较好但是弹体受到的载荷更大,此外气密环-减震垫横向支撑方式下,弹体出筒伴随较大的震荡过程,在今后研究中必须要重视振动问题。     

数值海浪对潜射导弹出水姿态影响研究

根据潜射战术导弹水下垂直运动的过程及特点,建立了导弹在水中及出水阶段的运动数学模型、推力矢量控制模型,分析了导弹水中和出水运动过程中5级海浪对导弹运动姿态的影响。通过仿真计算,得出了潜艇垂直发射战术导弹后,5级海况下导弹水中受控运动和无控运动时出水姿态的变化情况,为研究潜射导弹水中弹道提供了参考。     

超空泡航行体尾部流体动力特性试验研究

在水洞中采用前支撑方式模型进行了通气超空泡试验,对不同的超空泡形态下超空泡航行体尾部阻力系数、升力系数及俯仰力矩系数的变化规律进行了研究,并对航行体有无攻角情况下的尾部流体特性进行了比较,获得了攻角对尾部流体动力特性的影响。研究表明,在空泡开始包裹到尾部天平时,随着空泡形态的增长,尾部阻力系数迅速下降,而升力系数和俯仰力矩系数则迅速上升。当空泡将航行体上表面包裹,而下表面沾湿时,阻力系数减小趋势变平缓,而升力系数和俯仰力矩系数则均到达峰值。当空泡完全包裹航行体时,升力系数和俯仰力矩系数迅速回落至零值附近,此时阻力系数在零值附近变化不大。攻角1度情况下的航行体尾部阻力系数减小幅度与无攻角时相比明显降低,最大升力系数和俯仰力矩系数均远大于无攻角情况。     

回转体匀速垂直入水早期空泡数值模拟研究

基于VOF(Volume of Fluid)方法和有限体积法求解气、水两相流动的RANS方程,并结合动网格技术,对物体垂直入水空泡流动进行了数值计算研究。通过对球体垂直入水早期空泡形态进行数值计算,并将计算结果与May A 理想空泡模型拟合结果进行对比分析,二者具有较好的一致性,验证了数值计算方法的有效性。在此基础之上,进一步研究了150°锥角回转体垂直入水空泡生成过程,空泡壁面运动特性和空泡表面闭合特性,给出了垂直匀速入水空泡形态随时间变化规律,空泡壁面随入水过程时间变化运动规律,以及空泡表面闭合时间与入水速度之间的关系。     

爆破拆除塔架式钢烟囱塔架对筒体的影响研究

为了研究塔架式钢结构烟囱在爆破拆除倒塌过程中塔架对烟囱筒体的影响,以一座120m高塔架式钢烟囱的爆破拆除工程为背景,根据该烟囱的结构特点,对塔架和烟囱筒体的爆破切口分别进行参数设计,并运用LS-DYNA有限元分析软件进行建模计算,分析了数值模拟与实际倒塌过程时间差异的原因。在此基础上分别对烟囱筒体和塔架式钢烟囱建立模型进行数值求解,为方便对比分析,分别在2个模型中1~7段H型钢架临近的筒体处各选取一个监测点(共7个监测点),对各监测点的时间-应力曲线进行对比分析。分析表明:在塔架式钢烟囱在倒塌过程中,塔架倒塌速度大于筒体,能够加快筒体倒塌的进程,且塔架的助推作用会使筒体在倒塌过程中提前发生下坐现象。     

射流速度对气幕发射方式下航行体运动过程的影响研究

气幕发射方式是一种新型的航行体水下垂直发射方式。采用数值模拟的方法,研究了不同射流速度情况下航行体水下垂直发射过程中气幕形态、航行体表面压力及阻力特性等的变化规律,得到了在出筒过程中,不同气体射流速度情况下,航行体均可顺利通过气幕的最小半径处,气体射流马赫数越大,航行体总阻力系数越大;在出水过程中,航行体总阻力系数单调降低,与气体射流马赫数无关等结论。     

艇尾实尺桨空化初始航速和高频噪声谱的工程预报

为了实现艇尾实尺桨空化初始航速和高频噪声谱的工程预报,采用模型桨空化多相流模拟和实桨高频噪声谱半经验公式预报相结合的方法,预报了SUBOFF潜艇标称伴流下的实尺度7叶大侧斜桨的空化初始航速和高频噪声谱曲线以及特定频率1kHz处的谱源级。空化模拟和空化初生的较高预报精度由E779A桨的空化形态、空化面积和初生空化数的预报给予了校验。半经验公式的适用性由USS212型潜艇和Agosta-80潜艇的螺旋桨噪声预报给予了校验,精度适中。计算结果表明:7叶桨在水深16.8 m时空化初始航速为12.8 kn,6 kn航速下1 kHz处谱级为101.7 dB,较相同水深下Agosta-80潜艇临界航速高2.6 kn、谱级低0.3 dB,表明噪声性能更优。较好地建立了艇尾实尺桨空化初始航速和高频噪声谱预报的工程应用方法。     

悬臂方向对TLV空化抑制效果的影响及其机理

该文综合利用实验及数值模拟方法细致研究了悬臂式沟槽叶顶间隙泄漏涡(tip-leakage vortex, TLV)空化抑制器的悬臂凸出方向对抑制TLV空化效果的影响,并对其原因进行了深入讨论。研究表明:相比于原始水翼叶顶处的TLV空化,无论悬臂凸出方向指向水翼的吸力面还是压力面,悬臂式沟槽TLV空化抑制器在各个间隙大小下均能产生显著的抑制效果。相对而言,当所采用的悬臂凸出方向为压力面时,该装置对TLV空化的抑制效果更为显著,且可更有效地抑制TLV空化体积脉动。测量结果表明:悬臂凸出方向对水翼升、阻力系数影响均很小。数值结果则进一步表明:当采用悬臂凸出方向为指向压力面时,悬臂式沟槽TLV空化抑制器能更好地抑制流体从压力面流向吸力面,干扰TLV的生长,进而可以更加有效地抑制TLV空化的发展。     

苏门答腊岛西北海域大型海底滑坡过程反分析

针对苏门答腊岛西北海域大型海底滑坡,建立基于欧拉-欧拉多相流理论的滑坡模型,对滑坡体动态运动过程开展模拟反分析。通过与BING程序和解析模型结果对比,考虑土体分段软化后的多相流模型能够较好的重现该滑坡体的运动过程,能获得与实际海底滑坡相近的沉积形态和滑动距离。分析结果表明滑动首先从坡角较大处开始,并逐渐推动中、前部坡度较小处土体滑动;滑坡体整体启动后沿斜坡逐渐加速,当滑动至斜坡底部时端部峰值速度达到最大值43 m/s,之后逐渐减速并在深海平原处停止运动;土体扰动以及混水后土体强度降低是海底滑坡长距离运移的根本原因,同时滑动过程中滑坡体端部发生的滑水效应,减小了海床摩擦力的影响,增加了滑坡体的运动距离。     

A New Frangible Composite Canister Cover with the Function of Specified Direction Separation

A lightweight and auto-separated canister cover is required for quick launching in some specific missile launchers. In this paper, a new frangible composite canister cover with the function of specified direction separation is proposed and studied via both experimental and numerical approaches. The frangible canister cover with local non-split weak zone structure, which is manufactured by traditional hand lay-up process with vacuum assisted resin infusion (VARI) method, is designed to fail and separate in a predetermined and specified direction in comparison with the cover with full split weak zone structure. This design is innovative and also necessary for reduction of potential risk to peripheral equipment around the missile launcher. The failure pressure of the cover is determined on the basis of the failure criteria used in finite element (FE) model. In experimental pressurized testing, a number of frangible canister covers subjected to pressure loadings in six cases are studied. Close agreements between the experimental and numerical results have been examined. The frangible canister covers with local non-split weak zone structure which have been studied can be separated and fly out to the specified direction.     

Hydraulic Characteristics of Ranque-Hilsch Energy Separators

The hydraulic characteristics of an intensely swirling flow in the energy separation chambers in Ranque-Hilsch vortex tubes are investigated analytically and experimentally. Computer codes are developed and realized numerically for the calculation of the aggregate coefficient of hydraulic drag under conditions of swirling flow in an axisymmetric channel of a vortex tube. The results are treated in the form of criteria equations for the calculation of coefficients of hydraulic drag as functions of the basic process and geometric parameters of the vortex tube. The vortex tube hydraulics are studied experimentally, and the results of calculations performed using our procedure are compared with the data of numerical calculation using the commercially available CFX-TASCFlow package and with experimental data. Adequate agreement is observed between the experimentally obtained and numerical calculation results.     

Study of Subsonic Flow Over a TOW 2B Missile

The objective of this investigation is to study the subsonic flow over a missile. In this paper, a model of TOW 2B missile is studied. Two computational approaches are being explored, namely solutions based on the Reynolds-averaged compressible Navier-Stokes equations and solutions based on the inviscid flow (small disturbance theory). The simulations are performed at the Mach number of 0.6, 0.7, 0.8, 0.9 and 1.0 at four angles of attack of 2, 4, 6 and 8 degree. Results obtained from analytical simulation are compared with numerical data. It is found that lift and drag coefficients would go up by increasing of the angle of attack and the Mach number. Trend of changes of the results that obtained from the small disturbance theory is roughly as same as the numeric solution.     

空化模型中的相变系数影响研究

利用数值计算的方法,对空化模型中的相变系数进行研究.将数值计算和实验数据进行分析和整理,分别获得蒸发系数和冷凝系数与空化数之间的依赖关系.通过比较半球头圆柱体的二维轴对称模型数值计算结果表明:不同空化数对应着不同相变系数.其中,蒸发系数和冷凝系数分别对主空泡、次生空泡、尾空泡等类型的空泡在形态、溃灭位置、溃灭强度等方面有较大影响.     

The trans-critical heat transfer characteristics of LNG in a submerged combustion vaporizer under different operating pressures

It has been reported that trans-critical LNG vaporization process always occurs on the tube-side of typical submerged combustion vaporizer (SCV). In-depth analysis of this complex physical process is crucial for the stable operation of efficient SCV. In the present paper, a three-dimensional CFD numerical model was developed to analyze the flow and heat transfer characteristics of trans-critical LNG in the horizontal tube. Based on the numerical simulation results, the velocity, temperature and heat flux along the tube length were obtained. The distributions of local heat transfer coefficients under different operating pressures were also analyzed. The calculated results displayed that the representative phenomenon of “flow acceleration” occurs inside the horizontal serpentine tube. Affected by the variation of the physical properties, the heat transfer coefficient under the lower operating pressure was higher around pseudo-critical region, but decreased lower in the later field. Totally, the higher operating pressure may bring faster temperature rising and lower energy expenditure to reach the similar outlet temperature.     

Numerical simulation of cryogenic cavitating flow by an extended transport-based cavitation model with thermal effects

Thermodynamic effects on cryogenic cavitating flow is important to the accuracy of numerical simulations mainly because cryogenic fluids are thermo-sensitive, and the vapour saturation pressure is strongly dependent on the local temperature. The present study analyses the thermal cavitating flows in liquid nitrogen around a 2D hydrofoil. Thermal effects were considered using the RNG k-ε turbulence model with a modified turbulent eddy viscosity and the mass transfer homogenous cavitation model coupled with energy equation. In the cavitation model process, the saturated vapour pressure is modified based on the Clausius-Clapron equation. The convection heat transfer approach is also considered to extend the Zwart-Gerber-Belamri model. The predicted pressure and temperature inside the cavity under cryogenic conditions show that the modified Zwart-Gerber-Belamri model is in agreement with the experimental data of Hord et al. in NASA, especially in the thermal field. The thermal effect significantly affects the cavitation dynamics during phase-change process, which could delay or suppress the occurrence and development of cavitation behaviour. Based on the modified Zwart-Gerber-Belamri model proposed in this paper, better prediction of the cryogenic cavitation is attainable.