共查询到18条相似文献,搜索用时 312 毫秒
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旋转圆柱绕流的流场特性 总被引:1,自引:0,他引:1
在亚临界区Re=1.4×105条件下,基于大涡模拟(LES)方法对均匀来流作用下的旋转圆柱绕流进行了数值模拟。通过与非旋转时的实验和计算结果比较,验证了文中计算的准确性。在此基础上,对不同转速条件下(0≤α≤2,α为圆周线速度与自由来流速度的比值)的圆柱绕流进行了数值研究。结果表明,圆柱旋转可以有效地抑制其旋涡脱落,随着转速的增加,可大幅提高其升阻比,主要表现为阻力系数减小而升力系数线性增大。当α=2时,阻力系数和升力系数在经过短暂过渡期后达到稳定。 相似文献
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[目的]为探讨近壁旋转圆柱尾流及流体力特性,对典型间隙比下旋转圆柱绕流进行研究。[方法]对雷诺数Re=200下3种典型间隙比(G/D=0.2,0.8,1.4)的旋转圆柱绕流展开数值模拟,对比不同间隙比和转速比下的圆柱尾流及流体力特性。[结果]结果显示:当G/D=0.2时,圆柱表面脱涡会受到显著抑制,圆柱表面升阻力无波动;当G/D=0.8和1.4且转速比较低时,会发生“尾流涡”脱落现象,其结构与2S模式相似,升阻力系数呈正弦周期性波动,振幅较小;当正旋转速较大时,圆柱表面无漩涡脱落,形成稳定的D模式尾流(随转速比增大由D+模式变为D-模式),“尾流涡层”与“壁面涡层”发生分离,“壁面涡”呈现多周期性脱落现象,升阻力系数呈多周期波动,振幅显著增大;当反旋转速较大时,圆柱表面被一层正涡量的涡层包裹,漩涡脱落受到显著抑制,升阻力无波动。[结论]所得结论可为高效流动控制技术发展提供参考。 相似文献
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[目的]为探究有限长圆柱绕流的流动机理和特性,[方法]采用大涡模拟(LES)数值模型并结合涡识别方法,对三维有限长圆柱绕流进行数值模拟,并对有限长圆柱绕流进行验证和分析。[结果]模拟结果表明,有限长圆柱回流区相对较短,自由端的下洗作用会扰乱卡门涡街,导致阻力系数损失;相对于固定壁面,自由端面对顺流向速度影响更大;自由端面"蘑菇"涡成对出现,且存在2个流动源点;有限长圆柱流场存在更明显的三维特性,阻力系数更小;圆柱自由端后存在梢涡,圆柱与固定壁面交界处存在"马蹄"涡。[结论]所得结果可对有限长圆柱的流动特性进行相对全面的描述,对于理解和研究有限长圆柱绕流机理具有一定的参考价值。 相似文献
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利用风力助推转子辅助推进在实际工程中广泛应用,但以往的研究多局限于低雷诺数和单圆柱的范畴。本文基于重叠网格技术研究亚临界雷诺数范围内串列双圆柱体绕流,寻找合适的转速比实现航行器辅助推进。研究结果表明,旋转圆柱体产生的横向力可以为航行器提供辅助动力。然而转速比较大时,上下游圆柱产生的横向力差距变大,这对航行器的航向稳定性不利。要消除这种不利的影响,下游圆柱体需要更大的转速比才能平衡这个扭矩。随着转速比的增加,旋转圆柱体的尾涡由交替脱落转变为无明显的漩涡脱落,上游圆柱体对下游圆柱体的影响逐渐削弱。 相似文献
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海上平台是开采海洋资源的关键建筑,而支撑柱在平台中起着至关重要的作用。本文建立在海水作用下支撑柱做单圆柱绕流、串列双圆柱绕流和并列双圆柱绕流的二维流场模型,运用大涡模拟方法,对这3种模型进行数值模拟,得出其瞬时流场速度云图和圆柱受力特性曲线图。模拟计算层流和湍流情况下的圆柱绕流,通过模拟结果分析流场、升力系数和阻力系数的变化规律。 相似文献
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《船舶与海洋工程学报》2020,(3)
The hydrodynamic performance of a three-dimensional finite-length rotating cylinder is studied by means of a physical tank and numerical simulation. First, according to the identified influencing factors, a hydrodynamic performance test of the rotating cylinder was carried out in a circulating water tank. In order to explore the changing law of hydrodynamic performance with these factors, a particle image velocimetry device was used to monitor the flow field. Subsequently, a computational field dynamics numerical simulation method was used to simulate the flow field, followed by an analysis of the effects of speed ratio, Reynolds number, and aspect ratio on the flow field. The results show that the lift coefficient and drag coefficient of the cylinder increase first and then decrease with the increase of the rotational speed ratio. The trend of numerical simulation and experimental results is similar. 相似文献
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二维圆柱绕流数值模拟 总被引:1,自引:0,他引:1
对于椭球体绕流问题,可以考虑利用二维切片法的思想将其剖成一个个圆剖面,研究圆剖面的二维流动问题即二维圆柱绕流问题。采用Fluent软件,分别用多种流动模型在高雷诺数下对定常和非定常状态的圆柱绕流进行了数值模拟,计算得到圆柱绕流的升阻力系数、分离点位置、Strouhal数、流函数等结果,并与文献中的实验结果进行了比较,得到相应比较合理的计算模型。 相似文献
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应用有限元方法通过求解原始变量的二维不可压粘性流体的N-S方程和管线振动方程,数值模拟了近底管线的绕流及漩涡脱落引起的管线振动,采用ALE方法解决因管线振动引起的动网格问题和流固耦合问题。数值模拟了雷诺数90相似文献
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舵片是保证超空泡航行体运动稳定性和控制航行弹道的重要部分。文章基于均质平衡流模型和SST(Shear Stress Transport)湍流模型,计算了单独舵片的流体动力特性,并与试验数据进行了对比,结果符合较好,验证了计算模型的有效性。基于此方法,计算了单独舵片发生空化后在不同操舵状态下的非定常流体动力变化。结果表明,在攻角相同时,操舵状态下舵片的非定常升力系数和定常结果差别不大,而非定常阻力系数大于定常结果,并且操舵速度越快,阻力系数越大。另外计算了舵片发生空化后的流体动力系数,结果显示在攻角相同时,舵片的阻力系数和升力系数均小于其在全湿状态下的结果;在空化状态下,舵片升力系数的斜率小于全湿状态,并且舵片升力系数的斜率是变化的,存在某临界攻角,攻角大于此临界值时,升力系数的斜率减小,而此临界攻角恰好为舵片的吸力面刚刚出现空化时的攻角;操舵状态下舵片的阻力系数和升力系数的变化规律与定常结果一致,但是数值偏小。 相似文献
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A series of physical experiments were performed in steady current to investigate the hydrodynamic interactions between the cylinder and nets which constitute a main part of offshore aquacultural platforms. The hydrodynamic characteristics of only the cylinder, only nets and combined cylinder-net structures are measured and analyzed systematically under different current velocities, inflow angles and solidity ratios of nets. Based on experimental data, fitted formulas for hydrodynamic coefficients of a single resin net are proposed and compared to previously published empirical formulas. It is observed that the existence of the cylinder brings an increment up to 9.2% to drag coefficient of net panels whose solidity ratios are higher than 0.347, whereas this effect is negligible for nets with lower solidity ratios and perpendicular to the inflow. For nets inclined with 45°, the increment of the drag coefficient of net panels due to the existence of the cylinder is more significant (up to 22.9%) than that for perpendicularly placed nets. Furthermore, the existence of nets also leads to a noticeable increase in the drag coefficient of the cylinder, up to 40.18% for a relatively large net solidity ratio of 0.458, representative of biofouling condition. The increment increases with the rise of the solidity ratio of nets and it is larger for nets placed perpendicularly to the inflow than inclined. Effects of the cylinder and nets on lift coefficients of each other are a bit complicated, leading to an increase or reduction of lift coefficients depending on the inflow velocity, inflow angle and net solidity ratios. Finally, it is worth noting that the hydrodynamic interaction between the cylinder and nets deserves to be considered in current practice of hybrid methods by combining potential flow theory, Morison and screen models for aquacultural structures, especially for biofouling conditions. 相似文献
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Fatemeh Namazi-saleh Velluruzhathil John Kurian Zahiraniza Mustaffa Mohammadreza Tahan Dokyun Kim 《船舶与海洋工程学报》2017,16(1):81-86
The effect of rigid bed proximity on flow parameters and hydrodynamic loads in offshore pipelines exposed to turbulent flow is investigated numerically. The Galerkin finite volume method is employed to solve the unsteady incompressible 2D Navier–Stokes equations. The large eddy simulation turbulence model is solved using the artificial compressibility method and dual time-stepping approach. The proposed algorithm is developed for a wide range of turbulent flows with Reynolds numbers of 9500 to 1.5×104. Evaluation of the developed numerical model shows that the proposed technique is capable of properly predicting hydrodynamic forces and simulating the flow pattern. The obtained results show that the lift and drag coefficients are strongly affected by the gap ratio. The mean drag coefficient slightly increases as the gap ratio increases, although the mean lift coefficient rapidly decreases. The vortex shedding suppression happen at the gap ratio of less than 0.2. 相似文献
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The cross-section geometry of a submerged floating tunnel (SFT) has a large effect on hydrodynamic characteristics, structural behavior and service level, making the tunnel cross section the primary factor in optimizing efficiency. Minimizing the mean drag and the dynamic variability in the lift of the SFT cross section under bi-directional (i.e., tidal) flow has a dramatic impact on the reduction of structural displacements and mooring loads. Based on a parametric Bézier curve dynamically comprising the leading-edge radius, tunnel height and width to define the SFT geometry, a sensitivity analysis of the Bézier curve parameters for a fixed aspect ratio with prototype dimensions under uniform flow conditions was conducted by applying Computational Fluid Dynamics (CFD), and the pressure distribution around the SFT cross-section surface was analyzed. A theoretical method comprising the Kármán vortex street parameters was employed to verify the CFD simulation results. In order to determine the SFT cross section with optimal hydrodynamic properties, the mean drag and Root Mean Square (RMS) lift coefficients were selected as optimization objectives, and four Bézier curve parameters were the input variables, in a neural network and genetic algorithm optimization process (a hybrid BP-GA structure), which is less likely to become trapped in local minima. The results show the optimal tunnel cross section has a mean drag and a RMS lift coefficient reduced by 0.9% and 6.3%, respectively, compared to the original CFD dataset. 相似文献