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采用理想可压缩流体无旋定常流动及超空泡尾部Riabushinsky闭合方式假定,基于水动力学势流理论及细长体理论,建立了描述水下亚声速条件下细长锥型射弹超空泡流动的积分微分方程。发展了求解该方程的数值离散方法,提出多种超空泡外形初始解,分析了它们对超空泡形态计算结果的影响,优化了计算过程,简化了初始迭代条件。分析了流体压缩性对超空泡流动参数的影响,当马赫数大于0.3时,超空泡外形、射弹表面压力系数及射弹运动压差阻力系数均明显增大。计算得到的超空泡流动参数与相关文献的理论和实验结果吻合良好。 相似文献
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超空泡射弹是水下防御技术的研究热点之一。水下毁伤试验费用大,成本高,陆上等效试验是一种可能的替代方案。为此需要获得水下超空泡射弹侵彻条件下目标与相关材料的等效关系。以MK48-5鱼雷为对象,构建由壳体和14个关键部件组成的典型鱼雷结构模型。考虑水介质对侵彻的影响,将水下超空泡射弹侵彻鱼雷的过程分为两个阶段(a. 射弹侵彻水介质和鱼雷壳体,b. 射弹侵彻鱼雷内部关键部件);建立水介质耗能模型和靶板耗能模型;依据极限穿透速度等效原则和能量等效原则,分别得出两个阶段目标和等效靶之间的靶板厚度关系;为了获得射弹垂直命中鱼雷不同方向及不同工况毁伤效果,需要对纵向侵彻全雷和横向侵彻鱼雷战雷段、控制段、燃料舱和后舱雷尾4个典型舱段分别进行研究;并基于此建立了水下侵彻和不同工况条件下射弹侵彻鱼雷的多层等效靶模型。 相似文献
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认识带尾喷流和自然超空泡的水下高速航行体流体动力特性并发展其预报与控制方法仍是水动力学领域极具挑战性的课题.本研究采用CFD方法对尾喷流和自然超空泡之间的相互作用进行了数值研究.针对发动机欠膨胀超音速喷流,采用现有实验结果验证了基于两方程湍流模型的二维轴对称流动数值模型的可靠性.尾喷流在空气和蒸汽环境中流动的数值计算结果表明,由于蒸汽环境中背压较低,欠膨胀尾喷流无法及时形成压缩波,使得蒸汽环境中尾喷流的过膨胀区和气相扩散区的体积比空气中大;尾喷流很难形成规则的激波格栅,波系结构相对简单.针对携尾喷流的平头航行体超空泡流状态的数值模拟结果表明,尾喷流注入超空泡后迅速充满航行体周围的空腔区域;尾喷流与超空泡尾迹区域形成的回射流相互作用最终导致超空泡断裂,断裂过程中伴随着燃气泡的下泄现象;受空泡壁面约束,尾喷流难以在狭窄的超空泡空腔内完全膨胀,尾喷流的激波波系结构有显著的变化:在喷嘴附近受到压缩,在远离喷嘴区域受到超空泡水汽掺混的破坏;空泡内压强基本维持在饱和蒸汽压附近,没有显著增加. 相似文献
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细长体后部非定常超空泡研究 总被引:2,自引:2,他引:0
采用积分方程方法,研究了轴对称细长体后部非定常超空泡问题.应用时间有限差分离散化方法,对积分方程进行了求解.以细长锥体空化器为例,文中分别给出了当锥角和空化数改变(简称扰动)时,空泡长度和形状的变化规律.当流场周期扰动时,分析计算了超空泡的尺度变化.分别采用本文方法和理论公式,对空泡长度与空化数的关系曲线进行了对比.数值结果表明,扰动周期越短,空泡长度的变化越小;在相同的扰动频率下,空泡越长,时间滞后越长;空泡长度相同时,扰动频率越高,时间滞后越长.在高频脉冲扰动下,有脉冲波形沿着空泡表面传播,其传播速度为来流速度.在周期小扰动情况下,扰动波形沿着空泡表面传播,传播速度也是来流速度.本文得到的数值结果为水下航行体空化器的分析和设计提供参考作用. 相似文献
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应用有限体积方法求解三维可压缩雷诺平均N-S方程,计算了巡航导弹外形飞行器作小振幅俯仰运动时的动态绕流流场和空气动力特性,开展了导弹绕不同转轴、以不同频率和在不同迎角范围内进行俯仰运动的非定常气动力迟滞特性研究。计算结果表明,当导弹作快速俯仰运动时,在上仰和下俯过程中的同一迎角瞬间,绕导弹流场流动明显不同,表现出明显的非定常迟滞特性。导弹的非定常气动力迟滞特性随俯仰运动频率的增大明显增强,且气动力迟滞曲线随着俯仰轴位置的变化而变化。在同一减缩频率下,导弹在不同迎角范围内作周期俯仰运动时,相同的运动相位角所对应的升力系数对迎角的导数是一致的,而不同减缩频率下升力系数对迎角的导数随运动相位角变化曲线明显不同。 相似文献
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The water flow over a semicircular weir is investigated numerically and experimentally in this paper. The numerical model
solves the Reynolds equation for a mean flow field with thek-ε-turbulent model. To trace the motion of the free surface, the COF method with geometric reconstruction is employed. The
velocity of the flow is measured by means of LDV technique. Four types of flow patterns, the position of the separation and
reattachment point, the distribution of shear stress on the bed at downstream of the weir are presented and discussed. The
numerical results agree well with the experiment data. 相似文献
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Numerical and experimental investigation on droplet dynamics and dispersion of a jet engine injector
In the case of turbine combustors operating with liquid fuel the combustion process is governed by the liquid fuel atomization and its dispersion in the combustion chamber. By highly unsteady flow field conditions the transient interaction between the liquid and the gaseous phase is of interest, because it results in a temporal variation of air–fuel ratio which leads to a fluctuating temperature distribution. The objective of this research was the investigation of transient flow field phenomena (e.g. large coherent structures) on droplet dynamics and dispersion of an isothermal flow (of inert water droplets) as a necessary first step towards a full analysis of spray combustion in real-life devices. The advanced injector system for lean jet engine combustors PERM (Partial Evaporated Rapid Mixing) was applied, generating a dilute polydispersed spray in a swirled flow field. Experiments were performed using Phase Doppler Anemometry (PDA) and a patternator to determine the droplet polydispersity, concentration maps, and velocity profiles in the flow. An important finding is the effect of large-scale coherent structures due mainly to the precessing of the vortex core (PVC) of the swirling air jet on the particle dispersion patterns. The experimental results then serve as reference data to assess the accuracy of the Eulerian–Lagrangian computations using a Large Eddy Simulation (LES), a Unsteady Reynolds-Average Navier–Stokes Simulation (URANS) and two simplified (steady-state) simulations. There, a simplified droplet injection model was used and the required boundary conditions of injected droplet sizes were obtained from measurements. Important transient effects of deterministic droplet separation observed during experiments, could be perfectly replicated with this injection model. It is convincingly shown, through extensive computations, that the resolution of instantaneous vortical structures is indeed crucial; hence the LES, or a reasonably-well resolved URANS are preferred over the steady-state solutions with additional, stochastic-type, turbulent dispersion models. 相似文献
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The problem of methane hydrate decomposition in a reservoir saturated with a gas and hydrate mixture is investigated numerically. The results of the numerical simulation and an analytic solution obtained in the linear approximation are compared. It is shown that for high-permeability rocks the convective heat transfer in the near-well space of the reservoir predominates over the conductive transfer. This makes the use of intra-well heaters ineffective. It is found that an increase in the reservoir and well pressures and a decrease in the permeability suppress the formation of an extended hydrate dissociation region. Critical diagrams of existence of the frontal decomposition regime are constructed. 相似文献
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M. Salinas-Vázquez W. Vicente E. Martínez E. Barrios 《International Journal of Heat and Fluid Flow》2011,32(5):876-888
Large eddy simulation of natural convection in a confined square cavity is described. The use of a complex compressible code with an artificial acoustic stiffness correction method, allows the use of higher time steps for a faster time and statistical convergence. We consider a broadly studied experimental case, consisting of a natural convective flow in a confined square cavity, with vertical walls heated at different rates (active walls), set at Ra = 1.58 × 109. Turbulent boundary layers developing on the active walls and a vertical stable stratification characterize the mean flow. It is shown here that the results of this study match the experimental results reported in literature; for instance, mean velocity results. Although results for rms velocity fluctuations are barely over-predicted, the peak region is properly represented, while the greatest disagreements are found in the turbulent heat flow rate (velocity–temperature correlations). Turbulent structures were identified using different visualization methods and statistical studies. The authors found that the boundary layers on the active walls almost reach the fully turbulent regime, tending toward the laminar regime along the horizontal walls. 相似文献
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This paper demonstrates that a numerical method based on the generalized simplified marker and cell (GENSMAC) flow solver and Youngs' volume of fluid (Y‐VOF) surface‐tracking technique is an effective tool for studying the basic mechanics of hydraulic engineering problems with multiple free surfaces and non‐hydrostatic pressure distributions. Two‐dimensional flow equations in a vertical plane are solved numerically for this purpose. The numerical results are compared with experimental data and earlier numerical results based on a higher‐order depth‐averaged flow model available in the literature. Two classical problems, (i) flow in a free overfall and (ii) flow past a floor slot, are considered. The numerical results correspond very well with the experimental data for both sub‐critical and supercritical flows. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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This paper presents results of the numerical study of a piston-driven unsteady flow in a pipe with sudden expansion. The piston closes the larger-diameter pipe and moves between two limiting positions with strong acceleration or deceleration at the beginning and end of each stroke and constant velocity in between. The piston velocity in the exhaust stroke is about four times higher than in the intake stroke. Periodic piston movement in this fashion creates a complex unsteady flow between the piston head and the plane of sudden expansion. The numerical method is implicit and of finite volume type, using a moving grid and a collocated arrangement of variables. Second-order spatial discretization, fine grids and a multigrid solution method were used to ensure high accuracy and good efficiency. Spatial and temporal discretization errors were of the order of 1% and 0.1% respectively. The features of the flow are discussed and the velocity profiles are compared with experimental data, showing good qualitative and quantitative agreement. 相似文献
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Large-eddy simulation (LES) was used to study the influence and the resulting flow mechanisms of active flow control applied to a two-dimensional vehicle geometry. The LES results were validated against existing Particle Image Velocimetry (PIV) and force measurement data. This was followed by an exploration of the influence of flow actuation on the near-wake flow and resulting aerodynamic forces. Not only was good agreement found with the previous experimental study, but new knowledge was gained in the form of a complex interaction of the actuation with the coherent flow structures. The resulting time-averaged flow shows a strong influence of the extension of the actuation slots and the lateral solid walls on the near-wake flow structures and thereby on the resulting drag. 相似文献
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采用SIMPLEC算法对Ghost叶轮的三维非定常流场进行了数值模拟。利用计算所得流场结果并结合Lighthill和Lowson声学方程计算了由叶片表面非定常脉动力产生的气动噪声。计算结果表明:气动噪声的峰值主要集中在基频及其谐波附近;与静止的点声源相比,运动的点声源不仅使声场存在明显的多普勒效应,还会使声场的强度产生较大的变化;但对转速恒定的旋转点声源,加速度的变化对声场的影响可以忽略;从声场的分布来看,整个旋转叶轮可以看成是一个按简谐变化的偶极子源,数值计算结果与理论分析的结果吻合良好。 相似文献