检索结果-南通市图书馆

Analytic derivation of Monin-Obukhov similarity function for open atmospheric surface layer

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2021年第3期64卷 73-83页

作者： Yong Ji zhen-su she State Key Laboratory for Turbulence and Complex Systems and Department of Mechanics and Engineering Science College of EngineeringPeking UniversityBeijing100871China

The Monin-Obukhov(MO)similarity functionφm of the atmospheric surface layer(ASL)describing the deviation from the log law of the canonical turbulent boundary layer because of thermal stratification has been traditionally determined *** study presents a unified analytic expression derived from a symmetry-based theory of wall turbulence,called structural ensemble dynamics(SED),which postulates a generalized dilation symmetry principle expressing the effect of the wall on turbulence,leading to an analytic multi-regimes expression for the mixing *** ASL in unstable and stable conditions(i.e.,UC and SC),a unified two-regime formula of the mixing length is proposed,leading to aφm,similar to the Businger-Dyer(BD)formula;with a simplified model energy balance equation,φm is completely specified with no free ***,the theory allows the study of the open ASL’s underlying additional physical processes such as bottom-up or top-down flux due to pressure variations *** that Tp is decomposed into shear-like and buoyancy-like components,we propose new explanations for two important features of typical ASL:a significantly smaller Karman constant of 0.36 and a varyingφm for SC mean speed *** theory is validated by the data obtained at Kansas and also at Qingtu Lake Observation Array in Northern China for a variety of heat flux *** conclusion,due to pressure variations,we assert that ASL is intrinsically open and that the current theory offers a new basis for its quantification.

关键词： Monin-Obukhov similarity theory open atmospheric surface layer boundary layer turbulence symmetry-based analysis

Analytic prediction for planar turbulent boundary layers

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2016年第11期59卷 51-57页

作者： Xi Chen zhen-su she State Key Laboratory for Turbulence and Complex Systems and Department of Mechanics College of EngineeringPeking University

Analytic predictions of mean velocity profile(MVP) and streamwise(x) development of related integral quantities are presented for flows in channel and turbulent boundary layer(TBL), based on a symmetry analysis of eddy length and total stress. Specific predictions include the relations for momentum Reynolds number(Reθ) with friction Reτ and streamwise Re_x: Re_θ≈ 3.27Re_τ,and Re_x/Re_θ = 4.94(lnRe_θ + 1.88)~2 + 1; the streamwise development of the friction velocity u_τ: U_e/u_τ≈ 2.22 lnRe_x + 2.86. 3.83ln(lnRe_x), and of the boundary layer thickness δ_e: x/δ_e ≈ 7.27 lnRe_x.5.***.12.52ln(lnRe_x), which are fully validated by recent reliable data.

关键词： turbulent boundary layer symmetry analysis eddy length log law

Precise drag prediction of airfoil flows by a new algebraic model

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2020年第1期36卷 35-43页

作者： Meng-Juan Xiao zhen-su she State Key Laboratory for Turbulence and Complex Systems College of EngineeringPeking UniversityBeijing100871China

We report the results of accurate prediction of lift(C L)and drag(C D)coefficients of two typical airfoil flows(NACA0012 and RAE2822)by a new algebraic turbulence model,in which the eddy viscosity is specified by a stress length(SL)function predicted by structural ensemble dynamics(SED)*** accuracy of the prediction of C D with error of a few counts(one count is 10−4)and of C L with error under 1%-2%are uniformly obtained for varying angles of attack(AoA),indicating an order of magnitude improvement of drag prediction accuracy compared to currently used models(typically around 20 to 30 counts).More interestingly,the SED-SL model is distinguished with fewer parameters of clear physical meaning,which quantify underlying turbulent boundary layer(TBL)with a universal multi-layer structure,and is thus promising to be more easily generalizable to complex *** use of the new model for the calibration of flow condition in experiment and the extraction of flow physics from numerical simulation data of aeronautic flows are discussed.

关键词： Lift and drag coefficients Airfoil Flows Stress Length Structural ensemble dynamics

New perspective in statistical modeling of wall-bounded turbulence

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2010年第6期26卷 847-861页

作者： zhen-su she Xi Chen You Wu Fazle Hussain State Key Laboratory for Turbulence and Complex Systems and Department of Mechanical and Aerospace Engineering College of EngineeringPeking University100871 BeijingChina Department of Mechanical Engineering University of Houston HoustonTX 77204-4792USA

Despite dedicated effort for many decades,statistical description of highly technologically important wall turbulence remains a great *** models are unfortunately incomplete,or empirical,or *** a review of the existing theories of wall turbulence,we present a new framework,called the structure ensemble dynamics （SED）,which aims at integrating the turbulence dynamics into a quantitative description of the mean *** SED theory naturally evolves from a statistical physics understanding of non-equilibrium open systems,such as fluid turbulence, for which mean quantities are intimately coupled with the fluctuation *** from the ensemble-averaged Navier-Stokes（EANS） equations,the theory postulates the existence of a finite number of statistical states yielding a multi-layer picture for wall ***,it uses order functions（ratios of terms in the mean momentum as well as energy equations） to characterize the states and transitions between *** of the SED analysis to an incompressible channel flow and a compressible turbulent boundary layer shows that the order functions successfully reveal the multi-layer structure for wall-bounded turbulence, which arises as a quantitative extension of the traditional view in terms of sub-layer,buffer layer,log layer and wake. Furthermore,an idea of using a set of hyperbolic functions for modeling transitions between layers is proposed for a quantitative model of order functions across the entire flow *** conclude that the SED provides a theoretical framework for expressing the yet-unknown effects of fluctuation structures on the mean quantities,and offers new methods to analyze experimental and simulation *** with asymptotic analysis,it also offers a way to evaluate convergence of *** SED approach successfully describes the dynamics at both momentum and energy levels, in contrast with all prevalent approaches describing the mean velocity profile

关键词： Wall turbulence Statistical modeling Structure ensemble dynamics Order function Multi-layer

Wavy structures in compressible mixing layers

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2013年第5期29卷 633-640页

作者： Jun Chen Xiao-Tian Shi Tie-Jin Wang zhen-su she State Key Laboratory for Turbulence and Complex Systems College of Engineering China Academy of Aerospace Aerodynamics

Semi-periodic structures namely inclined wavy structures （IWS） are experimentally observed in compressible mixing layers at two convective Mach numbers （Mc = 0.11 and 0.47）. Flow structures are visualized by the laserinduced planar laser Mie scattering （PLMS） technique. Two methods are developed to investigate the spatial distribu- tion and geometry of IWS：（1） the dominant mode extrac- tion （DME） method, to extract the dominant modes of IWS from the streamwise gray-level fluctuation, and （2） the phase tracking （PT） method, to identify the shape of IWS. The re- sults suggest that pressure perturbations account for the for- marion of IWS in the initial mixing region and the joint effect of dilatation and coherent vortices enhances IWS in the well- developed region. The large transverse （cross-flow） scale of the IWS and their relation to coherent vortices （CV） indicate that the disturbance originated from CV in the mixing center propagates far into the free streams. The DME and the PT method are shown to be the effective tools to study the geometrical features of wavy structures in compressible shear flows.

关键词： Compressible mixing layer. Growth rate. Visu- alization Structures Coherent vortex

Numerical simulations of compressible mixing layers with a discontinuous Galerkin method

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2011年第3期27卷 318-329页

作者： Xiao-Tian Shi Jun Chen Wei-Tao Bi Chi-Wang Shu zhen-su she State Key Laboratory for Turbulence and Complex Systems and Dept. Mechanical and Aerospace Engineering College of EngineeringPeking University100871 BeijingChina Division of Applied MathematicsBrown UniversityProvidence RI 02912USA Division of Applied Mathematics Brown University Providence RI 02912 USA

Discontinuous Galerkin（DG） method is known to have several advantages for flow simulations,in particular,in fiexible accuracy management and adaptability to mesh refinement. In the present work,the DG method is developed for numerical simulations of both temporally and spatially developing mixing layers. For the temporally developing mixing layer,both the instantaneous fiow field and time evolution of momentum thickness agree very well with the previous results. Shocklets are observed at higher convective Mach numbers and the vortex paring manner is changed for high compressibility. For the spatially developing mixing layer,large-scale coherent structures and self-similar behavior for mean profiles are investigated. The instantaneous fiow field for a three-dimensional compressible mixing layer is also reported,which shows the development of largescale coherent structures in the streamwise direction. All numerical results suggest that the DG method is effective in performing accurate numerical simulations for compressible shear fiows.

关键词： Compressible mixing layer - Discontinuous Galerkin method . Self-similarity . Coherent structure

Boundary layer structure in turbulent rayleigh-bénard convection in a slim box

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2019年第4期35卷 713-728页

作者： Hong-Yue Zou Wen-Feng Zhou Xi Chen Yun Bao Jun Chen zhen-su she State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering Science College of Engineering Peking University Beijing 100871 China Department of Mechanics College of Engineering Sun Yat-sen University Guangzhou 510275 China

Logarithmic boundary layers have been observed in different regions in turbulence. However, how thermal plumes correlate to the log law of temperature and how the velocity profile changes with pressure gradient are not fully understood. Here, we perform three-dimensional simulations of turbulence in a slim-box without the front and back walls with aspect ratio, width:depth:height=L:D:H=1:1/6:1width:depth:height=L:D:H=1:1/6:1 (respectively corresponding to xx, yy and zz coordinates), in the Rayleigh number Ra=[1×10^8,1×10^10]Ra=[1×10^8,1×10^10] for Prandtl number Pr=0.7Pr=0.7. To investigate the structures of the viscous and thermal boundary layers, we examine the velocity profiles in the streamwise and vertical directions (i.e. UU and WW) along with the mean temperature profile throughout the plume-impacting, plume-ejecting, and wind-shearing regions. The velocity profile is successfully quantified by a two-layer function of a stress length, e^+u=e^+0(z^+)3/2[1+(z^+/z^+sub)4]^1/4eu+=e^+0(z+)3/2[1+(z+/zsub+)4]1/4, as proposed by she et al.(J Fluid Mech, 2017), though it is neither \pb type nor logarithmic. In contrast, the temperature profile in the plume-ejecting region is logarithmic for all simulated cases, being attributed to the emission of thermal plumes. The coefficient of the temperature log-law, AA, can be described by composition of the thermal stress length ■■θ0■θ0■ and the thicknesses of thermal boundary layer z■subzsub■ and z?bufzbuf■, i.e. A■z?sub/(■■θ0z■buf3/2)A■zsub?/(■θ0■zbuf^3/2). The adverse pressure gradient responsible for turning the wind direction contributes to intensively emitting plumes and the logarithmic temperature profile at the plume-ejecting region. The Nusselt number scaling and the local heat flux in the slim box are consistent with previous results of the confined cells. Therefore, the slim-box RBC is a preferable system for investigating in-box kinetic and thermal structures of turbulent convection with the large-scale circulation

关键词： Rayleigh-Bénard convection Wall-bounded turbulence Heat transport Direct numerical simulation

A symmetry-based length model for characterizing the hypersonic boundary layer transition on a slender cone at moderate incidence

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Advances in Aerodynamics 2022年第1期4卷 546-568页

作者： Wei-Tao Bi Zhou Wei Ke-Xin zheng zhen-su she State Key Laboratory for Turbulence and Complex Systems and Department of Mechanics and Engineering Science College of EngineeringPeking UniversityBeijing100871China Science and Technology on Scramjet Laboratory China Aerodynamics Research and Development CenterMianyang621000China State Key Laboratory of Aerodynamics China Aerodynamics Research and Development CenterMianyang621000China Computational Aerodynamics Institute China Aerodynamics Research and Development CenterMianyang621000China

The hypersonic boundary layer(HBL)transition on a slender cone at moderate incidence is studied via a symmetry-based length model:the SED-SL *** SED-SL specifies an analytic stress length function(which defines the eddy viscosity)describing a physically sound two-dimensional multi-regime structure of transitional boundary *** studies showed accurate predictions,especially on the drag coefficient,by the SED-SL for airfoil flows at different subsonic Mach numbers,Reynolds numbers and angles of ***,the SED-SL is extended to compute the hypersonic heat transfer on a 7∘half-angle straight cone at Mach numbers 6 and 7 and angles of attack from 0∘to 6∘.It is shown that a proper setting of the multi-regime structure with three parameters(i.e.a transition center,an after-transition near-wall eddy length,and a transition width quantifying transition overshoot)yields an accurate description of the surface heat fluxes measured in wind *** good agreements between simulations and measurements are obtained from windward to leeward side of the cone,implying the validity of the multi-regime description of the transition independent of instability *** is concluded that a unified description for the HBL transition of cone is found,and might offer a basis for developing a new transition model that is simultaneously of computational simplicity,sound physics and greater accuracy.

关键词： Hypersonic boundary layer transition Transition model Cone Heat flux

Universal hierarchical symmetry for turbulence and general multi-scale fluctuation systems

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2009年第3期25卷 279-294页

作者： zhen-su she Zhi-Xiong Zhang State Key Laboratory for Turbulence and Complex Systems, College of Engineering, Peking University, 100871 Beijing, China State Key Laboratory for Turbulence and Complex Systems College of Engineering Peking University Beijing China

Scaling is an important measure of multi-scale fluctuation systems. Turbulence as the most remarkable multi-scale system possesses scaling over a wide range of scales. she-Leveque （SL） hierarchical symmetry, since its publication in 1994, has received wide attention. A number of experimental, numerical and theoretical work have been devoted to its verification, extension, and modification. Application to the understanding of magnetohydrodynamic turbulence, motions of cosmic baryon fluids, cosmological supersonic turbulence, natural image, spiral turbulent patterns, DNA anomalous composition, human heart variability are just a few among the most successful examples. A number of modified scaling laws have been derived in the framework of the hierarchical symmetry, and the SL model parameters are found to reveal both the organizational order of the whole system and the properties of the most significant fluctuation structures. A partial set of work related to these studies are reviewed. Particular emphasis is placed on the nature of the hierarchical symmetry. It is suggested that the SL hierarchical symmetry is a new form of the self-organization principle for multi-scale fluctuation systems, and can be employed as a standard analysis tool in the general multi-scale methodology. It is further suggested that the SL hierarchical symmetry implies the existence of a turbulence ensemble. It is speculated that the search for defining the turbulence ensemble might open a new way for deriving statistical closure equations for turbulence and other multi-scale fluctuation systems.

关键词： Turbulence. Scaling law. she-Leveque modelHierarchical symmetry Self-organization - Turbulenceensemble