共查询到20条相似文献,搜索用时 875 毫秒
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《工程热物理学报》2017,(12)
在低进口雷诺数下,低速轴流涡轮内部可能存在复杂的边界层转捩和分离流动。准确模拟边界层转捩和流动分离对低速轴流涡轮的气动设计具有重要意义。本文以某单级低速轴流涡轮为研究对象,采用大涡模拟方法对其在进口雷诺数为20000情况下的内部流动进行了数值模拟研究,并与前期采用全层流模型、S-A模型、Abu-GhannamShaw(AGS)转捩模型的模拟结果进行了对比,对比分析发现,大涡模拟结果与实验结果吻合更好,可以准确模拟该涡轮叶片吸力面的流动分离和叶片通道内的二次流动。由大涡模拟结果可以得出,静叶尾迹和分离使尾迹区的流体流动速度降低,但尾迹对流动角的影响较小。动叶入口低速微团在做周向运动的同时沿径向运动;高速微团主要沿周向运动。静叶叶片表面的分离流存在较大的由叶顶向叶根的径向的运动;动叶吸力面叶顶处也存在较大的分离流动. 相似文献
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DES模型在压气机亚音转子中的应用探讨 总被引:1,自引:0,他引:1
本文运用分离涡模拟(DES)方法研究了不同工况下压气机亚音转子的流动情况,分析了其时均与瞬时流场中顶部间隙泄漏流动和根部角区的流动分离.通过与S-A模型计算结果的对比表明,DES模型在模拟顶部泄漏流动及二次泄漏、泄漏流在转子下游与尾迹的干涉时能够捕捉到更强的旋涡结构,在模拟转子根部角区的分离时也能获得更为丰富的流动现象.对不同工况的DES计算表明负荷的上升会使泄漏涡形成的位置向上游移动,从而导致并加剧二次流动,并对叶栅下游泄漏涡与尾迹的干涉产生影响.对设计工况下瞬时流场的分析表明,泄漏涡在叶栅下游体现出周期性的强弱变化,近叶根分离区也体现出明显的非定常性. 相似文献
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《工程热物理学报》2016,(2)
采用数值模拟的方法研究了超音速流动中斜坡型、双排斜坡型和分裂斜坡型三种不同微尺度涡流发生器诱导的尾迹涡耗散过程和发展轨迹,并对比分析了不同结构涡流发生器布置对激波边界层干涉的控制作用效果。研究结果表明,研究的三种涡流发生器结构诱导的逆旋涡之间具有相互弱化作用。双排斜坡型涡流发生器诱导的逆旋涡之间的弱化作用最强,斜坡型涡流发生器次之,分裂斜坡型涡流发生器诱导的逆旋涡之间的弱化趋势最弱,涡量更易在下游边界层中得到保持。涡流发生器产生的逆旋涡在互相诱导的作用下逐渐向远离壁面边界层的方向移动,分裂斜坡型和双排斜坡型涡流发生器的尾迹涡远离壁面的运动轨迹均较斜坡型涡流发生器的尾迹涡更为平缓。双排斜坡型涡流发生器的尾迹涡远离壁面的趋势更显著弱于分裂斜坡型涡流发生器,有利于保持尾迹涡在边界层内部,提升边界层的抗分离能力。在两种因素综合作用下,双排斜坡型涡流发生器对激波边界层相互作用具有最优的控制效果,分裂斜坡型涡流发生器的控制效果次之。 相似文献
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高速飞行器表面不可避免的存在突起物并形成复杂流场, 从而引起飞行器气动特性和热载荷的变化; 同时, 突起物是流动控制的重要方法之一, 合适的突起物形状及安装位置对于改善冲压发动机进气道性能有重要意义. 本文采用基于纳米粒子的平面激光散射技术(NPLS)研究了马赫3.0来流边界层为层流的平板上三个不同高度圆台突起物绕流流场, 主要关注了突起物后方的尾迹边界层, 并采用高精度的显式五阶精度加权紧致非线性格式(WCNS-E-5)离散求解Navier-Stokes方程模拟了该流场. 获得了超声速圆台绕流精细流场结构, 观察到突起物后方尾迹区域边界层发展的过程. 结合实验和数值模拟结果可以发现, 当圆台高度接近或者小于当地边界层厚度时, 突起物对边界层的扰动非常弱, 圆台后方尾迹边界层能够维持较长距离的层流状态, 在边界层转捩阶段也有清晰的发卡涡结构出现; 反之, 边界层受到的扰动明显增大, 在突起物后方很快发展为湍流; 风洞噪声对本文研究圆台引起的边界层扰动有一定影响, 实验获得的边界层转捩位置要比数值结果靠前. 基于NPLS流场图像, 采用间歇性方法分析了圆台突起物后方边界层的特性, 对于高度大于边界层厚度的圆台其间歇性曲线较为接近并且更加饱满, 边界层的脉动也更为强烈. 相似文献
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非定常尾迹控制叶栅分离研究 总被引:1,自引:0,他引:1
本文采用大涡模拟对某大转角叶栅的非定常分离流动及其在非定常尾迹作用下的分离控制机理进行了数值分析。主要捕捉了两个特征频率:分离泡不稳定频率fshear和尾缘脱落涡频率fshed,研究了不同的激励频率、尾迹移动方向、随机脉动等激励特征控制流动分离的效果。结果显示:特定外部频率强化了分离剪切层中的K-H展向涡结构,fshed能同时影响分离区域和尾涡区域,fshear只能作用于分离区域;尾迹从吸力面向压力面移动时,分离结构表现出对来流周期性更明显的响应;进口随机脉动对破坏K-H展向涡结构非常有效。 相似文献
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绕流叶栅的尾涡脱落是诱发水力机械振动噪声的重要因素。本文以串列布置平板叶栅为研究对象,进行雷诺数Re=5000与10000下的叶栅绕流尾迹速度场的LDA测量实验,分析不同雷诺数下绕叶栅流场速度分布,探究涡脱频率特性。实验结果表明:同一雷诺数下平板尾迹区中心线上速度分布可分为回流区、快速增长区、缓慢增长区三个区域;双平板绕流场,下游平板的存在明显抑制了上游平板尾迹的发展,与单平板模型比回流区流向长度减小;雷诺数从5000增大到10000时,平板尾迹回流区的流向长度变小,但最低流速分布升高;下游平板的存在抑制了上游平板的涡脱,使其频率降低,上、下游平板涡脱频率一致。 相似文献
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The flow field around a rotationally oscillating circular cylinder in a uniform flow is studied by using a particle image
velocimetry to understand the mechanism of drag reduction and the corresponding suppression of vortex shedding in the cylinder
wake at low Reynolds number. Experiments are conducted on the flow around the circular cylinder under rotational oscillation
at forcing Strouhal number 1, rotational amplitude 2 and Reynolds number 2,000. It is found from the flow measurement by PIV
that the width of the wake is narrowed and the velocity fluctuations are reduced by the rotational oscillation of the cylinder,
which results in the drag reduction rate of 30%. The mechanism of drag reduction is studied by phase-averaged PIV measurement,
which indicates the formation of periodic small-scale vortices from both sides of the cylinder. It is found from the cross-correlation
measurement between the velocity fluctuations that the large-scale structure of vortex shedding is almost removed in the cylinder
wake, when the small-scale vortices are generated at the unstable frequency of shear layer by the influence of rotational
oscillation. 相似文献
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The aerodynamic noise and the wake flow field in a cooling fan under actual operating conditions are studied with and without
winglets on the fan blades. In order to understand the influence of the winglet, the aerodynamic noise and the wake velocity
distribution are measured. The results indicated that overall noise level decreased and the noise spectrum was changed in
a low frequency range when the winglet was installed. It was found from the flow visualization and PIV measurement that the
influence of the winglet appeared in the traces of the tip vortices and the magnitude of vorticity was reduced in the near
wake region, which suggest the observed reduction in aerodynamic noise 相似文献
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We use a combination of numerical simulations and experiments to elucidate the structure of the flow of an electrically conducting fluid past a localized magnetic field, called magnetic obstacle. We demonstrate that the stationary flow pattern is considerably more complex than in the wake behind an ordinary body. The steady flow is shown to undergo two bifurcations (rather than one) and to involve up to six (rather than just two) vortices. We find that the first bifurcation leads to the formation of a pair of vortices within the region of magnetic field that we call inner magnetic vortices, whereas a second bifurcation gives rise to a pair of attached vortices that are linked to the inner vortices by connecting vortices. 相似文献
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In this paper,the separation-induced transition in an LPT(low-pressure turbine)cascade is investigated at low Reynolds number with DNS(direct numerical simulation).The transition process is accurately predicted giving good agreements between the DNS and experimental results.To illustrate the secondary instability of separation-induced transition in a low-disturbance environment,the results are comprehensively analyzed in both Fourier space and physical space.It is illustrated that the effect of hyperbolic instability dominates around the saddle point of hyperbolic streamlines.This instability mechanism is responsible for the emergence of the streamwise vortices in the braid region.Elongated and intensified because of the“stretching”effect of the background flow,these vortices become the most noticeable characteristic of the flow field.Fundamental modes of small spanwise wavelength are excited in the braid region,so as some low-frequency modes.The elliptical instability plays a minor role than hyperbolic instability.It is also observed that the fundamental mode with a larger spanwise wavelength is unstable in the vortex core which is associated with the deformation of the vortex core via elliptical instability.There is no convincing evidence for the existence of subharmonic instability. 相似文献
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Hui Wang Guoliang Li 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2014,68(7):1-7
We have reported a theoretical study on the interaction mechanism between dust particles in the presence of asymmetric ion flow and an external magnetic field in complex plasma. The recent experimental and numerical results on the particle-wake interaction ensures the dominance of the wake effect in the subsonic regime of plasma flow using the cold ion approximation. The recent developments in dusty plasma research and its growing interest towards more realistic magnetized dusty plasma scenarios also demand serious attention to study the wake effect both in the sub and supersonic regimes in the presence of a magnetic field. It is a challenging task to develop a correct, quantitative theory of wake potential for different regimes of magnetic field and ion flow velocity. Analytic expressions for the wake potential have been reported in this paper for both subsonic and supersonic regimes in the presence of an external magnetic field along with Debye-Hückel type potentials. The results show that the wake potential plays a dominant role in the subsonic regime and its strength increases with an increase in magnetic field. The behaviour of the wake potential is found to have an interesting effect on the Coulomb crystallization of dust grains and is studied with the help of molecular dynamic (MD) simulation. 相似文献
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Jiang-Ping HuShou-Cheng Zhang 《Journal of Physics and Chemistry of Solids》2002,63(12):2277-2282
A key prediction of the SO(5) theory is the antiferromagnetic vortex state. Recent neutron scattering experiment on LSCO superconductors revealed enhanced antiferromagnetic order in the vortex state. Here we review theoretical progress since the original proposal and present a theory of static and dynamic antiferromanetic vortices in LSCO superconductors. It is shown that the antiferromagnetic region induced by the vortices can be greater than the coherence length, due to the light effective mass of the dynamic antiferromagnetic fluctuations at optimal doping, and close proximity to the antiferromagentic state in the underdoped regime. Systematic experiments are proposed to unambiguously determine that the field induced magnetic scattering originates from the vortices and not from the bulk. 相似文献
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M.S. Howe 《Journal of sound and vibration》1980,71(2):161-170
A theoretical model is examined to determine the influence of a slot in a thin airfoil on the unsteady lift caused by vortices shed into the wake. It is shown that at sufficiently low reduced frequencies based on the width of the slot, vorticity production at the edges of the slot can prevent penetration by the unsteady flow so that the airfoil behaves as if the slot were absent. There exists a range of frequencies, however, in which the magnitudes of both the lift and the accompanying radiated sound can be significantly reduced relative to their respective levels for the unslotted airfoil. 相似文献