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Non-equilibrium turbulent phenomena in the flow over a backward-facing ramp 预览
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作者 Le FANG Hongkai ZHAO +2 位作者 Weidan NI Jian FANG Lipeng LU 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第2期215-236,共22页
Non-equilibrium turbulence phenomena have raised great interests in recent years.Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows,e.g.,grid turbulence,turbulent wakes,a... Non-equilibrium turbulence phenomena have raised great interests in recent years.Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows,e.g.,grid turbulence,turbulent wakes,and homogeneous isotropic turbulence(HIT).The non-equilibrium turbulence in non-canonical flows,however,has rarely been studied due to the complexity of the flows.In the present contribution,a directnumerical simulation(DNS)database of a turbulent flow is analyzed over a backwardfacing ramp,the flow near the boundary is demonstrated,and the non-equilibrium turbulent properties of the flow in the wake of the ramp are presented by using the characteristic parameters such as the dissipation coefficient Cε and the skewness of longitudinal velocity gradient Sk,but with opposite underlying turbulent energy transfer properties.The equation of Lagrangian velocity gradient correlation is examined,and the results show that non-equilibrium turbulence is the result of phase de-coherence phenomena,which is not taken into account in the modeling of non-equilibrium turbulence.These findings are expected to inspire deeper investigation of different non-equilibrium turbulence phenomena in different flow conditions and the improvement of turbulence modeling. 展开更多
关键词 NON-EQUILIBRIUM TURBULENCE BACKWARD RAMP direct numerical simulation(DNS)
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Experimental and numerical study of flow structures of the second-mode instability 预览
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作者 Yiding ZHU 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第2期273-282,共10页
Flow structures of a Mach 6 transitional boundary layer over a 260 mm long flared cone are investigated by the particle image velocimetry(PIV).Particle images near the curved wall are initially transformed into surfac... Flow structures of a Mach 6 transitional boundary layer over a 260 mm long flared cone are investigated by the particle image velocimetry(PIV).Particle images near the curved wall are initially transformed into surface-fitted orthogonal coordinates and spliced with their 180°-symmetric images to satisfy a no-slip condition at the wall.The results are then reversely transformed to the physical domain.Direct numerical simulation(DNS)is also performed to validate the experimental results.The experimental and numerical results are in agreement,indicating a strong dilatation process within the second-mode instability. 展开更多
关键词 HYPERSONIC transition PARTICLE image velocimetry(PIV) direct numerical simulation(DNS)
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Effects of finite-size neutrally buoyant particles on the turbulent channel flow at a Reynolds number of 395 预览
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作者 Zhaosheng YU Chenlin ZHU +1 位作者 Yu WANG Xueming SHAO 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第2期293-304,共12页
A direct-forcing fictitious domain(DFFD)method is used to perform fully resolved numerical simulations of turbulent channel flows laden with large neutrally buoyant particles.The effects of the particles on the turbul... A direct-forcing fictitious domain(DFFD)method is used to perform fully resolved numerical simulations of turbulent channel flows laden with large neutrally buoyant particles.The effects of the particles on the turbulence(including the mean velocity,the root mean square(RMS)of the velocity fluctuation,the probability density function(PDF)of the velocity,and the vortex structures)at a friction Reynolds number of 395 are investigated.The results show that the drag-reduction effect caused by finite-size spherical particles at low particle volumes is negligibly small.The particle effects on the RMS velocities at Reτ=395 are significantly smaller than those at Reτ=180,despite qualitatively the same effects,i.e.,the presence of particles decreases the maximum streamwise RMS velocity near the wall via weakening the large-scale streamwise vortices,and increases the transverse and spanwise RMS velocities in the vicinity of the wall by inducing smaller-scale vortices.The effects of the particles on the PDFs of the fluid fluctuating velocities normalized with the RMS velocities are small,regardless of the particle size,the particle volume fraction,and the Reynolds number. 展开更多
关键词 TURBULENT channel flow FINITE-SIZE PARTICLE direct numerical simulation(DNS)
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The visualization of turbulent coherent structure in open channel flow 预览
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作者 Xiao-dong Bai Wei Zhang +3 位作者 Qing-he Fang Yong Wang Jin-hai Zheng An-xin Guo 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第2期266-273,共8页
Due to its multiscale and multi-layer natures,the coherent structures of turbulent in the open channel flow is complex and difficult to be visualized for understanding its evolution.In this paper,five types of methods... Due to its multiscale and multi-layer natures,the coherent structures of turbulent in the open channel flow is complex and difficult to be visualized for understanding its evolution.In this paper,five types of methods for the vortical structure in the fluids,namely the Q-criterion,the vorticity,the Omega method,the velocity-vorticity correlation structures(VVCS)as well as the most recent Rortex method,are adopted to visualize the turbulent flow in the open channel.With the free surface modelled as a free slip boundary,a direct numerical simulation(DNS)is carried out to study the multi-layered flow structure characteristics under the free surface.The visualization results by the Q-criterion,the vorticity,the Omega method and the Rortex are firstly analyzed.Then the turbulent flow layers near the free surface are identified with corresponding anisotropy indices.Afterwards,the VVCS within various turbulence layers are visualized accordingly.This research indicates that the VVCS can straightforwardly show the geometry information of the cohere nt structures of turbulent in different layers for the ope n channel flow. 展开更多
关键词 Open channel FLOW FLOW VISUALIZATION velocity-vorticity COHERENT structure direct numerical simulation(DNS)
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Direct numerical simulation of the viscoelastic channel flow using Giesekus model with variable parameters 预览
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作者 Wei-guo Gu Yu Li De-zhong Wang 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第2期326-332,共7页
The paper presents a direct numerical simulation(DNS)for the drag-reducing channel flow using the Giesekus model with variable parameters.It is assumed that the relaxation time in the constitutive equation is varied d... The paper presents a direct numerical simulation(DNS)for the drag-reducing channel flow using the Giesekus model with variable parameters.It is assumed that the relaxation time in the constitutive equation is varied depending on the local shear rate.The maximal drag reduction rate is obtained when variable parameters are applied in the Giesekus model at a high Weissenberg number.The Reynolds shear stress is reduced when the Weissenberg number increases.In this case,the turbulence generation and transportation are further weakened and increasingly approach to the values in the experiments. 展开更多
关键词 VISCOELASTIC FLUID Giesekus model direct NUMERICAL simulation(DNS) VARIABLE parameters
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Relationship between wall shear stresses and streamwise vortices in turbulent flows over wavy boundaries 预览
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作者 Lihao WANG Weixi HUANG +2 位作者 Chunxiao XU Lian SHEN Zhaoshun ZHANG 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第3期381-396,共16页
The relationship between wall shear stresses and near-wall streamwise vortices is investigated via a direct numerical simulation(DNS)of turbulent flows over a wavy boundary with traveling-wave motion.The results indic... The relationship between wall shear stresses and near-wall streamwise vortices is investigated via a direct numerical simulation(DNS)of turbulent flows over a wavy boundary with traveling-wave motion.The results indicate that the wall shear stresses are still closely related to the near-wall streamwise vortices in the presence of a wave.The wave age and wave phase significantly affect the distribution of a two-point correlation coefficient between the wall shear stresses and streamwise vorticity.For the slow wave case of c/Um=0.14,the correlation is attenuated above the leeward side while the distribution of correlation function is more elongated and also exhibits a larger vertical extent above the crest.With respect to the fastwave case of c/Um=1.4,the distribution of the correlation function is recovered in a manner similar to that in the flat-wall case.In this case,the maximum correlation coefficient exhibits only slight differences at different wave phases while the vertical distribution of the correlation function depends on the wave phase. 展开更多
关键词 direct NUMERICAL simulation(DNS) WALL SHEAR stress near-wall streamwise VORTEX TWO-POINT correlation
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高压环境下剪切稀化非牛顿撞击射流直接数值模拟
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作者 朱呈祥 郑浩铭 尤延铖 《航空学报》 EI CAS CSCD 北大核心 2019年第6期143-152,共10页
高压环境下的撞击射流是液体火箭推进系统中广泛采用的一种燃料雾化方法,其雾化效果将直接决定最终燃烧效率。采用直接数值模拟(DNS)工具,对10MPa高压环境下剪切稀化非牛顿直角撞击射流的三维非定常雾化特征、机理及非牛顿特性进行了研... 高压环境下的撞击射流是液体火箭推进系统中广泛采用的一种燃料雾化方法,其雾化效果将直接决定最终燃烧效率。采用直接数值模拟(DNS)工具,对10MPa高压环境下剪切稀化非牛顿直角撞击射流的三维非定常雾化特征、机理及非牛顿特性进行了研究。结果表明:高压环境下该撞击射流的雾化流场呈圆形辐射状分布并形成Mushroom头部和Ω状的局部凸起,气体中的涡量分布表现为有序贴附区和无序爆炸区两类,液膜向液丝的破碎主要受平均气体力和平均黏性力作用影响,而液丝向液滴的破碎则主要受局部流场参数影响,撞击雾化过程中液体无量纲表面积不断增长并可分为5个阶段。此外,撞击射流头部在局部强剪切力作用下其无量纲黏性系数最低降至仅0.7。 展开更多
关键词 撞击射流 非牛顿流体 高压环境 直接数值模拟(DNS) 剪切稀化
粗糙元诱导的高超声速转捩机理及应用 被引量:1
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作者 朱德华 袁湘江 杨武兵 《航空学报》 CSCD 北大核心 2018年第1期63-72,共10页
采用直接数值模拟(DNS)方法细致刻画了不同类型粗糙元诱导的高超声速边界层从层流到湍流的转捩过程,从拓扑结构稳定性和边界层流动稳定性两个角度分析了不同类型粗糙元诱导转捩的机理。通过对不同类型粗糙元诱导转捩机理的研究,设计... 采用直接数值模拟(DNS)方法细致刻画了不同类型粗糙元诱导的高超声速边界层从层流到湍流的转捩过程,从拓扑结构稳定性和边界层流动稳定性两个角度分析了不同类型粗糙元诱导转捩的机理。通过对不同类型粗糙元诱导转捩机理的研究,设计了一种对齿型粗糙元,其具有小尺度、低摩阻、低热流、诱导转捩能力强的特点。研究发现不同类型的粗糙元底部区域均存在鞍点-结点-鞍点(SNS)型轨线,在扰动的作用下其会形成非定常、非对称的振荡结构。同时针对斜坡型以及对齿型粗糙元的工程应用开展了研究,验证了不同类型粗糙元诱导转捩的机理,为强制转捩装置设计提供了基础理论支撑。 展开更多
关键词 粗糙元 直接数值模拟(DNS) 高超声速 转捩机理 拓扑结构
分层环境中异重流运动问题的直接数值模拟 预览
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作者 梁小龙 乔文丽 赵西增 《浙江大学学报:工学版》 CSCD 北大核心 2018年第5期996-1001,1013共7页
为了研究线性分层环境下的开闸式异重流运动过程的问题,采用改进的高精度直接数值模拟(DNS)模型,在正交坐标系下,以DNS为基本求解器,实现物质运输方程和Navier-Stokes方程同步求解.采用距离函数平滑初始状态的不连续运输方程,利用具... 为了研究线性分层环境下的开闸式异重流运动过程的问题,采用改进的高精度直接数值模拟(DNS)模型,在正交坐标系下,以DNS为基本求解器,实现物质运输方程和Navier-Stokes方程同步求解.采用距离函数平滑初始状态的不连续运输方程,利用具有六阶精度的迎风紧致差分格式(UCCD)改进原模型,更准确地求解物质输运方程.通过求解一维对流方程和入侵重力流的模拟结果验证了模型的可靠性.开展泥沙异重流与线性分层环境掺混过程的研究,并获得了高精度数值结果,可以更好地捕捉中间入侵的异重流产生的内波效果.结果表明:该模型不仅可以准确模拟入侵异重流卷吸分层环境水体的过程,还可以准确模拟头部运动位置、异重流卷吸沉降以及能量转换等问题. 展开更多
关键词 迎风紧致差分格式 直接最值模拟(DNS) 线性分层 泥沙沉降 能量转化
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剪切稀化非牛顿射流撞击液膜破碎直接数值模拟
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作者 朱呈祥 吴猛 +1 位作者 陈荣钱 尤延铖 《航空学报》 CSCD 北大核心 2018年第5期87-95,共9页
液态射流撞击是液体火箭推进系统中广泛采用的一种燃料雾化方法,其破碎特征直接影响燃料最终的掺混及燃烧效率。采用直接数值模拟(DNS)工具,研究了低雷诺数(Rel=41)和中等韦伯数(Wel=163)条件下剪切稀化非牛顿射流撞击液膜破碎的... 液态射流撞击是液体火箭推进系统中广泛采用的一种燃料雾化方法,其破碎特征直接影响燃料最终的掺混及燃烧效率。采用直接数值模拟(DNS)工具,研究了低雷诺数(Rel=41)和中等韦伯数(Wel=163)条件下剪切稀化非牛顿射流撞击液膜破碎的问题,着重分析了对角液膜的三维结构、破碎特征和非牛顿特性等。研究结果表明:在所研究的射流参数下,该非牛顿撞击液膜破碎属于Open Rim类别,破碎过程具有三维特性并伴随液丝与边缘的融合、液丝向液滴的转变等时域流动特征。液体的总表面积随时间不断增长,但单位表面积随液膜破碎的发生而下降,液膜扩张半角随时间逐渐增加并趋于恒定值43°,而后部液膜的长度几乎不随时间发生变化。此外,撞击液膜表现出明显的剪切稀化特性,液体内部最低黏性系数仅为零剪切黏性系数的1/5。 展开更多
关键词 撞击射流 非牛顿流体 液膜破碎 直接数值模拟(DNS) 剪切稀化
离散式粗糙元诱导翼型边界层转捩的数值和实验研究 预览 被引量:1
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作者 董昊 刘是成 +1 位作者 杨鲤铭 朱志斌 《南京航空航天大学学报》 CSCD 北大核心 2018年第6期807-814,共8页
在Ma=0.6来流条件下,针对三维离散式圆柱粗糙元诱导NACA0012翼型边界层转捩问题开展了直接数值模拟(Direct numerical simulation,DNS)和油膜干涉风洞实验研究,分析了粗糙元诱导转捩的机理及粗糙元高度和相邻粗糙元间距对转捩位置的影... 在Ma=0.6来流条件下,针对三维离散式圆柱粗糙元诱导NACA0012翼型边界层转捩问题开展了直接数值模拟(Direct numerical simulation,DNS)和油膜干涉风洞实验研究,分析了粗糙元诱导转捩的机理及粗糙元高度和相邻粗糙元间距对转捩位置的影响。结果表明,翼型表面粗糙元能够通过诱导出三维Λ涡和马蹄涡促进边界层转捩,达到转捩控制的效果。粗糙元高度和相邻粗糙元间距对边界层转捩有影响,且增加粗糙元高度和减小相邻粗糙元间距能够促进转捩。粗糙元高度对转捩的影响大于粗糙元间距,且对粗糙元后方区域影响大,对相邻粗糙元中间区域影响小。 展开更多
关键词 离散式粗糙元 边界层转捩 直接数值模拟 油膜干涉 风洞实验
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Characteristics of turbulence transport for momentum and heat in particle-laden turbulent vertical channel flows 预览
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作者 Caixi Liu Shuai Tang +1 位作者 Lian Shen Yuhong Dong 《力学学报:英文版》 SCIE EI CAS CSCD 2017年第5期833-845,共13页
The dynamic and thermal performance of particleladen turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with... The dynamic and thermal performance of particleladen turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in conjunction with heat transfer enhancement in particle-laden turbulent flows. The effects of particles on momentum and heat transfer are analyzed, and the possibility of drag reduction in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed.We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow, which shows the heat transfer reduction when large inertial particles with low specific heat capacity are added to the flow. However, we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved. The present results show that particles, which are active agents, interact not only with the velocity field, but also the temperature field and can cause a dissimilarity in momentum and heat transport. 展开更多
关键词 Direction numerical simulation (DNS) LAGRANGIAN tracking approach FLOW drag HEAT transfer Particle-laden FLOW
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Near-wall behaviors of oblique-shock-wave/turbulent-boundary-layer interactions 预览
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作者 Mingsheng YE Ming DONG 《应用数学和力学:英文版》 SCIE EI CSCD 2017年第10期1357-1376,共20页
有 33.2 的一个事件角度的一个倾斜的冲击波上的直接数字的模拟( DNS )??鮼诧?髧??闧花??軦??蒚?龋?华??鮼??軥鮊鷥?????鮼裥?????????????????????鮼??????が?鮼
关键词 湍流边界层 相互作用 斜激波 近壁 直接数值模拟 特性 压力梯度 速度分布
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Boundary-layer disturbances subjected to free-stream turbulence and simulation on bypass transition 预览
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作者 Hong QIN Ming DONG 《应用数学和力学:英文版》 SCIE EI CSCD 2016年第8期967-986,共20页
The phenomena associated with the entrainment of free-stream turbulence(FST) into boundary-layer flows are relevant for a number of subjects.It has been believed that the continuous spectra of the Orr-Sommerfeld(O-S)/... The phenomena associated with the entrainment of free-stream turbulence(FST) into boundary-layer flows are relevant for a number of subjects.It has been believed that the continuous spectra of the Orr-Sommerfeld(O-S)/Squire equations describe the entrainment process,and thus they are used to specify the inlet condition in simulation of bypass transition.However,Dong and Wu(Dong,M.and Wu,X.On continuous spectra of the Orr-Sommerfeld/Squire equations and entrainment of free-stream vortical disturbances.Journal of Fluid Mechanics,732,616–659(2013)) pointed out that continuous spectra exhibit several non-physical features due to neglecting the non-parallelism.They further proposed a large-Reynolds-number asymptotic approach,and showed that the non-parallelism is a leading-order effect even for the short-wavelength disturbance,for which the response concentrates in the edge layer.In this paper,the asymptotic solution is verified numerically by studying its evolution in incompressible boundary layers.It is found that the numerical results can be accurately predicted by the asymptotic solution,implying that the latter is adequate for moderate Reynolds numbers.By introducing a series of such solutions as the inflow perturbations,the bypass transition is investigated via the direct numerical simulation(DNS).The transition processes,including the evolution of streaks,the amplification of secondary-instability modes,and the emergence of turbulent spots,agree with the experimental observations. 展开更多
关键词 free-stream turbulence(FST) bypass transition boundary layer ASYMPTOTIC direct numerical simulation(DNS)
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Effect of particles on turbulent thermal field of channel flow with different Prandtl numbers 预览
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作者 Caixi LIU Yuhong DONG 《应用数学和力学:英文版》 SCIE EI CSCD 2016年第8期987-998,共12页
The direct numerical simulation(DNS) of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed.The focus of this paper is on the modulation of the particles on turbulent t... The direct numerical simulation(DNS) of heat transfer in a fully developed non-isothermal particle-laden turbulent channel flow is performed.The focus of this paper is on the modulation of the particles on turbulent thermal statistics in the particle-laden flow with three Prandtl numbers(P r = 0.71,1.5,and 3.0) and a shear Reynolds number(Reτ = 180).Some typical thermal statistics,including normalized mean temperature and their fluctuations,turbulent heat fluxes,Nusselt number and so on,are analyzed.The results show that the particles have less effects on turbulent thermal fields with the increase of Prandtl number.Two reasons can explain this.First,the correlation between fluid thermal field and velocity field decreases as the Prandtl number increases,and the modulation of turbulent velocity field induced by the particles has less influence on the turbulent thermal field.Second,the heat exchange between turbulence and particles decreases for the particle-laden flow with the larger Prandtl number,and the thermal feedback of the particles to turbulence becomes weak. 展开更多
关键词 direct numerical simulation(DNS) Prandtl number PARTICLE thermal statistic channel flow
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剪切来流中圆盘近尾迹的数值研究 预览
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作者 钱万益 杨渐志 +3 位作者 顾海林 姚梦云 赵普 刘明侯 《中国科学技术大学学报》 CAS CSCD 北大核心 2016年第10期853-859,
采用直接数值模拟(DNS)方法对低雷诺数时剪切来流中圆盘近尾迹进行了数值研究,重点研究剪切率对尾迹结构的影响.选取的雷诺数是140,160和300,无量纲进口来流剪切率范围是0≤k<0.1.当Re=140和160时,尾迹均变为非稳态面对称结构,表明... 采用直接数值模拟(DNS)方法对低雷诺数时剪切来流中圆盘近尾迹进行了数值研究,重点研究剪切率对尾迹结构的影响.选取的雷诺数是140,160和300,无量纲进口来流剪切率范围是0≤k<0.1.当Re=140和160时,尾迹均变为非稳态面对称结构,表明剪切来流中非稳态面对称模态出现的临界雷诺数减小.剪切来流中发夹涡头部在来流速度较高侧明显偏大,且当Re=160时对称面位置随剪切率的增加而逐渐趋于xoy面.当Re=300时,剪切来流中圆盘尾迹结构没有明显变化,仍呈弱紊乱状态.研究还发现,相较于均匀来流,在k值较低(k<0.1)的剪切来流中无量纲涡旋脱落频率基本不变. 展开更多
关键词 圆盘尾迹 剪切流 直接数值模拟(DNS)
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槽道紊流中涡旋倾角的概率密度分布特征 被引量:1
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作者 陈槐 李丹勋 +1 位作者 王浩 王兴奎 《应用基础与工程科学学报》 EI CSCD 北大核心 2016年第4期661-671,共11页
以Del-Alamo等(2004)直接数值模拟的槽道紊流数据为基础,对比两种涡旋方向的计算方法(涡量矢量和速度梯度张量的实特征向量),并统计了涡旋与3个切面(XZ,XY及YZ)间倾角的概率密度分布.研究结果表明,在缓冲层内,涡量矢量与实特征向量存在... 以Del-Alamo等(2004)直接数值模拟的槽道紊流数据为基础,对比两种涡旋方向的计算方法(涡量矢量和速度梯度张量的实特征向量),并统计了涡旋与3个切面(XZ,XY及YZ)间倾角的概率密度分布.研究结果表明,在缓冲层内,涡量矢量与实特征向量存在较大的差异;涡旋以准流向涡为主,其与XZ面的倾角很小,但与YZ面的倾角很大.在缓冲层外,涡量矢量与实特征向量的夹角较小,且概率密度最大的夹角稳定在10°附近;涡旋以发夹涡为主,与XZ面主要呈±45°倾角,与XY及YZ面主要呈±55°倾角.涡旋与切面间倾角的概率密度分布特征可以由Ω状发夹涡模型来解释. 展开更多
关键词 直接数值模拟 槽道流 涡量 实特征向量 准流向涡 发夹涡
Rotation invariant constitutive relation for Reynolds stress structure parameter 预览
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作者 Jinglei XU Zhengguang TU Ning HU 《应用数学和力学:英文版》 SCIE EI CSCD 2015年第4期517-522,共6页
A new Reynolds stress constitutive formula is constructed using the firstorder statistics of turbulent fluctuations instead of the mean strain rate. It includes zero empirical coefficients. The formula is validated wi... A new Reynolds stress constitutive formula is constructed using the firstorder statistics of turbulent fluctuations instead of the mean strain rate. It includes zero empirical coefficients. The formula is validated with the direct numerical simulation(DNS) data of turbulent channel flow at Reτ =180. The Reynolds stresses given by the proposed formula agree very well with the DNS results. The good agreement persists even after the multi-angle rotation of the coordinate system, indicating the rotation invariance of the formula. The autocorrelation of the fluctuating velocity rather than the mean strain rate is close to the essence of the Reynolds stress. 展开更多
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Dynamics and geometry of developing planar jets based on the invariants of the velocity gradient tensor 预览
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作者 吴楠楠 SAKAI Yasuhiko +1 位作者 NAGATA Kouji ITO Yasumasa 《水动力学研究与进展:英文版》 SCIE EI CSCD 2015年第6期894-906,共13页
Based on the direct numerical simulation(DNS), the developing planar jets under different initial conditions, e.g., the conditions of the exit Reynolds number and the exit mean velocity profile, are investigated. We m... Based on the direct numerical simulation(DNS), the developing planar jets under different initial conditions, e.g., the conditions of the exit Reynolds number and the exit mean velocity profile, are investigated. We mainly focus on the characteristics of the invariants of the velocity gradient tensor, which provides insights into the evolution of the dynamics and the geometry of the planar jets along with the flow transition. The results show that the initial flow near the jet exit is strongly predominated by the dissipation over the enstrophy, the flow transition is accompanied by a severe rotation and straining of the flow elements, where the vortex structure evolves faster than the fluid element deformation, in the fully-developed state, the irrotational dissipation is dominant and the most probable geometry of the fluid elements should remain between the biaxial stretching and the axisymmetric stretching. In addition, with a small exit Re and a parabolic profile for the exit mean streamwise velocity, the decay of the mean flow field and the magnitude of the turbulent variables will be strengthened in the process of the flow transition, however, a large exit Re will promote the flow transition to the fully-developed state. The cross-impact between the exit Re and the exit mean velocity profile is also observed in the present study. 展开更多
关键词 平面射流 速度梯度 几何形状 不变量 张量 动力学 直接数值模拟 平均速度
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Numerical investigation of turbulent channel flow controlled by spatially oscillating spanwise Lorentz force 预览
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作者 Wentang WU Yanji HONG Baochun FAN 《应用数学和力学:英文版》 SCIE EI CSCD 2015年第9期1113-1120,共8页
A formulation of the skin-friction drag related to the Reynolds shear stress in a turbulent channel flow is derived. A direct numerical simulation(DNS) of the turbulent control is performed by imposing the spatially o... A formulation of the skin-friction drag related to the Reynolds shear stress in a turbulent channel flow is derived. A direct numerical simulation(DNS) of the turbulent control is performed by imposing the spatially oscillating spanwise Lorentz force. Under the action of the Lorentz force with several proper control parameters, only the periodically well-organized streamwise vortices are finally observed in the near-wall region. The Reynolds shear stress decreases dramatically, especially in the near-wall area, resulting in a drag reduction. 展开更多
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