超空泡射弹尾拍结构动力学响应分析

超空泡射弹在运动过程中存在尾拍现象,导致结构发生振动,影响射弹的弹道稳定性,降低射弹结构的可靠性。该文建立了射弹无约束动力学方程,使用有限元法求解得到了超空泡射弹在尾拍载荷作用下的动力学响应,并对射弹的加固模型进行了分析,给出了环状加强筋个数、直径以及间距对降低射弹振幅效果的影响。研究结果表明：超空泡射弹在尾拍运动过程中转动周期和幅值随加强筋个数的增大而增大;射弹头部的弹性振动幅值随加强筋个数和直径的增大而减小,振动周期亦随加强筋个数的增大而减小;加强筋距离的减小,对于降低射弹中部振幅效果明显,但对射弹头部的振动几乎没有影响。     

空化器形状对超空泡射弹尾拍运动影响的数值研究

为研究空化器形状对超空泡射弹尾拍航行时运动特性的影响,基于有限体积法和Mixture多相流模型,结合动网格技术构建了三维自由尾拍运动仿真模型,在两种长径比下比较了平头弹、凹口弹、锥头弹的尾拍运动特性,并分析了其水动力影响因素。结果表明：较小长径比下,平头弹可以保持运动稳定,凹口弹和锥头弹易失稳,主要是由于空化器产生的空泡尺寸差异导致其临界失稳攻角依次降低。较大长径比下,临界失稳攻角消失,三种头型射弹均能保持尾拍稳定,锥头弹在速度较高时以“单侧尾拍”保持稳定,速度降低后以“双侧尾拍”保持稳定,而平头弹和凹口弹始终以“双侧尾拍”保持稳定;锥头弹由于“单侧尾拍”会产生与初始扰动方向相反的垂直位移,而平头弹和凹口弹由于弹头升力产生与初始扰动方向相同的垂直位移。     

自然超空泡形态特性的射弹试验研究

利用高速射弹试验对自然超空泡的形态特性和发展规律进行了深入研究。试验采用了不同尺寸的试验弹,射弹最大速度可达70m/s,最小空化数可达0.04。获得了水下航行体的自然超空泡形态参数随空化数变化的规律,并与相关文献中使用的经验公式进行了对比,在小空化数下一致性较好。研究结果表明,高速射弹试验是研究自然超空泡形态特性的一种有效手段,能够捕捉到大量超空泡水动力学现象,证实了自然超空泡的直径和长度都随空化数的增大而减小,且呈指数规律。     

变速超空泡航行体壳结构的动力响应分析

通过对变速超空泡水下航行体壳结构受力模型的分析,建立了恒定推力下航行体的平面运动方程,确定了变速过程中的阻力和冲击力。利用有限元方法,进行了结构响应计算,分析了减速过程中节点时域上的最大应力值在轴向的分布情况及典型节点处的响应。结果表明：航行体所需推力和所受应力较大,对其结构强度要求较高;运动过程中,节点时域上的最大应力在空间域上的极大值主要分布在首尾端部和柱壳中部;存在一些振动频率对航行体结构响应影响显著。结果对超空泡航行体壳结构受力和强度分析以及优化设计有着重要的指导意义。&;#61472;     

水下超空泡航行体非线性动力学建模与仿真

超空泡技术可以大幅提高水下航行速度,根据空泡膨胀独立性原理,研究了空泡的记忆效应及其对空泡形态和航行体尾部滑行力等流体动力的影响,在计算超空泡航行体各部分所受的流体动力的过程中考虑了空化器的定向效应和空泡尾部的上漂变形,还研究了航行过程中尾翼浸水深度变化时尾翼效率的变化规律,从而建立了更加精确的超空泡航行体动力学模型。通过仿真分析了超空泡航行体运动的稳定性,最后设计了非线性控制策略来进行深度跟踪。     

基于空泡记忆效应的水下超空泡航行体建模与控制

利用超空泡可以大幅地提高水下航行体的速度,为了研究超空泡航行体的动力学建模和控制问题,根据空泡膨胀独立性原理,研究了空泡的记忆效应及其对空泡形态的影响,详细计算了超空泡航行体各部分所受的流体动力,计算过程中还考虑了空化器定向效应和空泡上飘变形,研究了航行过程中尾翼效率变化规律,建立了一种更精细的超空泡航行体非线性动力学模型。设计了基于输入输出精确线性化的鲁棒极点配置控制器,仿真结果表明实现了系统在一定初始扰动下的稳定控制。     

楔形体诱导的非定常超空泡计算

采用积分方程方法,研究了楔形体外部自然超空泡流问题。提出了楔形体在静止流体中做变速运动所引起的非定常超空泡的积分方程。作为特例,得到了均匀来流时非定常超空泡的积分方程。应用时间有限差分离散化方法和有限差分法对积分方程进行了求解,得到了楔形体做变速运动、楔角变化、空化数变化、小扰动空化流等各种情况下的数值解。数值结果表明:非定常超空泡具有时滞性和波动性。楔体做变速运动时,加速度越大,时间滞后越长。在匀减速运动时,空泡不封闭,可能有回注射流发生。扰动频率越高,空泡长度变化越小,时间滞后越长。扰动以波动形式沿着空泡表面传播,传播速度为来流速度。该文所得到的结果,对于非定常超空化水翼的设计和分析能够起到参考作用。     

空泡外形对超空泡航行体机动回转运动影响

提出超空泡航行体空泡流型概念,将航行体外形、空泡外形、航行体外形与空泡外形匹配统一用超空泡航行体空泡流型描述,用定量关系表达超空泡航行体流体动力特性;建立机动回转运动超空泡数学模型,推导回转运动超空泡外形表达式;研究超空泡航行体由直航运动过渡到稳态机动回转运动过程,给出该过程中超空泡外形变化规律;分析角速度、离心力对机动回转运动超空泡外形影响,揭示该两因素对超空泡外形变化影响程度;以空泡外形与航行体外形匹配为约束,对机动能力进行初步评估,通过仿真计算获得表征航行体机动能力的临界回转角速度。     

通气超空泡水下射弹实验研究

利用射弹装置开展了通气超空泡水下射弹的实验研究。对水下射弹进行通气,得到了水下射弹的通气超空泡,并对空泡的形态进行了研究;得到了不同空化数条件下形成超空泡的通气率：空化数较大时较低的通气率,能形成超空泡,空化数较小时,形成通气超空泡的通气率较高;对超空泡减阻特性进行了验证,比较了同样初速度的通气超空泡射弹与不通气射弹速...     

周期性来流扰动对通气超空泡航行体流体动力特性的影响EI北大核心CSCD

利用滑移网格法,数值研究了周期性来流扰动对通气超空泡航行体流体动力特性的影响,通过上游两片水翼反向摆动使下游流场产生水平速度周期性变化的来流条件,分析来流扰动对航行体空泡形态及流体动力的影响。在周期性水平来流作用下通气超空泡截面发生颈缩现象,航行体易产生沾湿区域影响空泡减阻效果;分析了航行体在周期性来流扰动下的流体动力变化规律,发现当航行体被空泡完全包裹时,阻力呈现周期性波动,升力较小;当航行体被空泡局部包裹时,升力和阻力都会产生较大波动。通过沾湿面积比率分析周期性来流的波长和波幅对空泡形态的影响规律,为空泡在扰动环境中的稳定性研究奠定了基础。     

Dissipation of the mechanical energy of a subsonic stream of compressible fluid with change in direction

An analysis is made of the influence of viscosity and thermal conductivity of a compressible fluid on the process of dissipation of the mechanical energy of a stream decelerated in a region where its direction changes.     

On compressible subsonic flow between impeller and casing of radial-flow compressors with superposed throughflow

Summary Subject of this paper is the numerical investigation of the flow between impeller and casing of compressors of radial construction. The solution procedure is based on implicite difference equations, in which parameters of material such as heat conductivity, viscosity and density are variable. Because of the assumption of low density, laminar flow conditions are assumed. The computation method makes possible the determination of the torque coefficient as a function of Reynolds-and Mach number as well as of geometry and superposed throughflow.With 3 Figures     

Coherent detection in Doppler global velocimetry: a simplified method to measure subsonic fluid flow fields

The principles of an entirely new method to demodulate Doppler signals in Doppler global velocimetry (DGV) are discussed. The method makes use of coherent detection and streak imaging to record both temporal and spatial information on a single image. The method retains the simplicity of the basic DGV technique yet increases its applicability to subsonic flow regimes. The combination of a straightforward optical configuration and the ability to collect large data sets efficiently make this technique particularly useful in high-cost experimental facilities such as wind-tunnel testing where large quantities of data must be collected in a relatively short time period.     

Attachment-line heating in a compressible flow

The attachment-line boundary layer on a swept wing can be subject to either an instability or contamination by wing-root turbulence. A model of the attachment-line boundary layer is first developed including compressibility and wall heating in a Falkner–Skan–Cooke class of three-dimensional boundary layers with a Hartree parameter of 1.0. This is verified with other formulations in the literature. For cases otherwise subcritical to either contamination or instability, the destabilizing effect of leading-edge heating under a variety of sweep angles and flight conditions is demonstrated. The results correlate with the attachment-line Reynolds number. Because the required heating levels are reasonable and achievable to trip the flow over the wing to turbulent, one possible application of this work is in the establishment of a baseline turbulent flow (on demand) for the calibration of a laminar-flow-control health-monitoring system.     

On compressible flow in a rotating cylinder

Summary Axisymmetric steady flow of a perfect gas in a rotating cylinder is studied by applying a linearised analysis to a small perturbation about isothermal rigid body rotation. Motivated by present day gas centrifuges, special attention is focussed on the effect of a length-to-radius ratio which increases from unit magnitude to infinity and on the effect of a strong radial density gradient associated with the isothermal rigid body rotation. The Ekman number E _*based on the small radial density scale and the density at the cylinder wall is taken to be small. It appears that the flow outside Ekman boundary layers at the end caps consists of three types. These correspond to 1 L _* E _* ^{% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyOeI0YaaS% qaaSqaaiaaigdaaeaacaaIYaaaaaaa!386D!\[ - \tfrac{1}{2}\]} E _* ^{% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyOeI0YaaS% qaaSqaaiaaigdaaeaacaaIYaaaaaaa!386D!\[ - \tfrac{1}{2}\]} L _*, E _* ^–1 andE _* ^–1 L _* where L _*is the ratio of the cylinder-length to the radial density scale. For 1 L _* E _* ^{% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyOeI0YaaS% qaaSqaaiaaigdaaeaacaaIYaaaaaaa!386D!\[ - \tfrac{1}{2}\]} an inviscid flow in a region of limited thickness near the cylinder wall is found. Due to the strong decrease of the density, radial diffusion is not confined to Stewartson boundary layers at the wall (typical for incompressible flow) but extends in the core. This finds expression in two layers in the centre of the cylinder, parallel to the rotation axis, having a structure similar to both Stewartson layers and adjusting the inviscid flow near the wall to a flow dominated by radial diffusion near the rotation axis. For L _* E _* ^{% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyOeI0YaaS% qaaSqaaiaaigdaaeaacaaIYaaaaaaa!386D!\[ - \tfrac{1}{2}\]} and L _* E _* ^–1 both Stewartson layers become successively of the same thickness as the density scale. At the same time the corresponding layers in the core go to the wall and join. As a result, for L _* E _* ^–1 radial diffusive processes are significant in the entire cylinder, a situation also known from studies of flows in semi-infinite gas centrifuges.     

BEM simulation of compressible fluid flow in an enclosure induced by thermoacoustic waves

The problem of unsteady compressible fluid flow in an enclosure induced by thermoacoustic waves is studied numerically. Full compressible set of Navier–Stokes equations are considered and numerically solved by boundary-domain integral equations approach coupled with wavelet compression and domain decomposition to achieve numerical efficiency. The thermal energy equation is written in its most general form including the Rayleigh and reversible expansion rate terms. Both, the classical Fourier heat flux model and wave heat conduction model are investigated.The velocity–vorticity formulation of the governing Navier–Stokes equations is employed, while the pressure field is evaluated from the corresponding pressure Poisson equation. Material properties are taken to be for the perfect gas, and assumed to be pressure and temperature dependent.     

Numerical modeling of projectile penetration into compressible rigid viscoplastic media

We develop computational methods for modeling penetration of a rigid projectile into porous media. Compressible rigid viscoplastic models are used to capture the solid–fluid transition in behavior at high strain rates and account for damage/plasticity couplings and viscous effects that are observed in geological and cementitious materials. A hybrid time discretization is used to model the non‐stationary flow of the target material and the projectile–target interaction, i.e. an explicit Euler method for the projectile equation and a forward (implicit) method for the target boundary value problem. At each time step, a mixed finite element and finite‐volume strategy is used to solve the ‘target’ boundary value problem. Specifically, the non‐linear variational inequality for the velocity field is discretized using the finite element method while a finite‐volume method is used for the hyperbolic mass conservation and damage evolution equations. To solve the velocity problem, a decomposition–coordination formulation coupled with the augmented Lagrangian method is adopted. Numerical simulations of penetration into concrete were performed. By conducting a time step sensitivity study, it was shown that the numerical model is robust and computationally inexpensive. For the constants involved in the model (shear and volumetric viscosities, cut‐off yield limit, and exponential weakening parameter for friction) that cannot be determined from data, a parametric study was performed. It is shown that using the material model and numerical algorithms that developed the evolution of the density changes around the penetration tunnel, the shape and location of the rigid/plastic boundary, the compaction zones, and the extent of damage due to air‐void collapse are described accurately. Copyright © 2007 John Wiley & Sons, Ltd.     

空气夹层对含液结构在球形弹体侵彻作用下动态响应的影响

基于一维应力波理论对高强水中冲击波在不同介质间的传播进行分析,提出了2种防护含液结构的空气夹层形式,建立了数值仿真模型。在验证数值仿真方法的基础上,分析了含液结构在弹体侵彻过程中空穴演化、冲击波传播、空气夹层结构变形等的动态变化过程及弹体速度衰减规律,讨论了不同舱室结构在球形弹体侵彻作用下的冲击波特点和结构不同组成部分的能量转换关系,对比了不同弹速下前后板的塑性变形。研究结果表明:(1)在含液结构中添加空气夹层能有效降低含液结构前板和后板的冲量、能量和塑性变形;(2)空气夹层影响前后板变形的主要原因为阻抗失配和空气夹层变形引起的稀疏波及液体空化;(3)从整体看,双层间隔板结构衰减前后板变形能力优于方格夹层板结构,但随着弹速的增加,双层间隔夹层板的前后壁变形相互制约,2种结构对含液塑性变形的改变逐渐接近。     

Calculation of compressible flow in a short vortex chamber

A method for calculating a compressible turbulent flow in a short vortex chamber that incorporates calculations of the boundary layer at the end walls by the integral method and of the discharge by the theory of an ideal atomizer has been proposed. The magnitudes of pressure and circulation on the radius of the outlet orifice of the chamber, obtained in determining the boundary layer, have been used as input parameters in calculating the discharge, and the gas process has been regarded as isothermal. Favorable agreement between the calculated results and the experimental data has been found. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 152–158, September–October, 2006.     

Thermal effects in compressible viscous flow in a capillary

The thermal effects for a compressible viscous flow in a capillary have been calculated by solving the equation of energy, where a parabolic profile is assumed for the axial flow velocity. It is shown that, in general, the temperature changes are small (a few millikelvins), consistent with the current assumption of an isothermal flow, except in the case of a critical, i.e., very compressible, fluid where the cooling can be substantial. This effect is demonstrated numerically on the basis of a flow of ethylene in nearly critical circumstances.Paper dedicated to Professor Joseph Kestin.