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Direct numerical simulation of turbulent boundary layer over an anisotropic compliant wall

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Acta Mechanica Sinica 2019年第2期35卷 384-400页

作者： Qian-Jin Xia Wei-Xi Huang Chun-Xiao Xu AML Department of Engineering MechanicsTsinghua University Beijing 100084 China

Direct numerical simulation of a spatially developing turbulent boundary layer over a compliant wall with anisotropic wall material properties is performed. The Reynolds number varies from 300 to approximately 860 along the streamwise direction, based on the external flow velocity and the momentum thickness. Eight typical cases are selected for numerical investigation under the guidance of the monoharmonic analysis. The instantaneous flow fields exhibit the traveling wavy motion of the compliant wall, and the frequency-wavenumber power spectrum of wall pressure fluctuation is computed to quantify the mutual influence of the wall compliance and the turbulent flow at different wave numbers. It is shown that the Reynolds shear stress and the pressure fluctuation are generally enhanced by the wall compliance with the parameters considered in the present study. A dynamical decomposition of the skin-friction coefficient is derived, and a new term (CW) appears due to the wall-induced Reynolds shear stress. The influence of the anisotropic compliant wall motion on the turbulent boundary layer through the wall-induced negative Reynolds shear stress is discussed. To elucidate the underlying mechanism, the budget analysis of the Reynolds stresses transportation is further carried out. The impact of the wall compliance on the turbulent flow is disclosed by examining the variations of the diffusion and velocity-pressure correlation terms. It is shown that increase of the Reynolds stresses inside the flow domain is caused by enhancement of the velocity-pressure correlation term, possibly through the long-range influence of the wall compliance on the pressure field, rather than diffusion of the wall-induced Reynolds shear stress into the fluid flow.

关键词： Turbulent boundary layer Anisotropic compliant wall Direct numerical simulation Skin-friction coefficient Reynolds shear stress

Strong coupling between height of gaps and thickness of thermal boundary layer in partitioned convection system

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Chinese Physics B 2019年第9期28卷 270-275页

作者： Ze-Peng Lin Yun Bao Department of Mechanics Sun Yat-Sen University

A direct numerical simulation(DNS) method is used to calculate the partitioned convection system with Ra number ranging from 10^7 to 2×10^*** the boundary layer thickness to normalize the height of gaps d, we find a strong consistency between the variation of the TD number(the average value of the temperature in each heat transfer channel is averaged after taking the absolute values) with the change of the height of gaps and the variation of the TD number with the change of Ra number in partitioned *** a given thickness of partition, heights of gaps are approximately equal to 0.5 or 1 time of the thermal boundary layer thickness λθ at different Ra *** number representing temperature characteristics is almost the constant value, which means that TD number is a function of d/λθ *** of local temperature field of area in gaps shows that the temperature distribution in the gaps are basically the same when d/λθ is *** heat transfer Nu number of the system at d/λθ≈ 0.5 is larger than that of d/λθ≈ 1, both of them have the same scaling law with Ra number and Nu^Ra^0.25.

关键词： partitioned convection system height of gaps thermal boundary layer TD number

Enhancing aerodynamic performances of a high-turning compressor cascade via boundary layer suction

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Science China(Technological Sciences) 2010年第10期53卷 2748-2755页

作者： GUO Shuang1, CHEN ShaoWen1, LU HuaWei2, SONG YanPing1 & CHEN Fu1 1 School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China 2 Marine Engineering College, Dalian Maritime University, Dalian 116026, China School of Energy Science and Engineering Harbin Institute of Technology Harbin China Marine Engineering College Dalian Maritime University Dalian China

Experimental investigation was carried out to study the effect of suction positions and suction flow rates on the aerodynamic performance of a compressor cascade with a large camber angle. The ink-trace flow visualization was conducted and the flow fields of the cascade were also measured. Three types of boundary layer suction configurations are compared,i.e. the suction surface suction,the endwall suction and the compound suction. Experimental results show that the large amount of suction flow rate gains more losses reduction than the small amount for a certain proper suction configuration,but the speed of loss decline slows down as the suction flow rate goes on increasing. boundary layer suction on the suction surface obviously enhances the ability of the boundary layer around the midspan to withstand the negative pressure gradient of the flow passage. The range of the suction surface corner is also decreased. If the suction slot locates in the corner separation region where severe separation has happened,the flow separation will be terminated at the slot and redevelop downstream. And boundary layer suction on the endwall mainly influences the endwall corner region in remarkably delaying,lessening and reorganizing the corner separation. While the whole flow field is remarkably improved at both midspan and the corner region in the compound suction schemes. At higher suction flow rates,the aerodynamic performance of the compressor cascade is better than that with boundary layer suction simply on the suction surface or on the endwall. When the suction flow rate is 1.5% of the inlet mass flow,the compound suction scheme achieves a maximum loss reduction of 17% compared with the cascade without boundary layer suction.

关键词： boundary layer suction high-turning diffusion cascade suction flow rate suction position experimental investigation

Effect of boundary Scattering on Magneto-Transport Performance in BN-Encapsulated Graphene

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Chinese Physics Letters 2022年第9期39卷 57-61页

作者： Lijun Zhu Lin Li Xiaodong Fan Zhongniu Xie Changgan Zeng CAS Key Laboratory of Strongly Coupled Quantum Matter Physics and Department of PhysicsUniversity of Science and Technology of ChinaHefei 230026China International Center for Quantum Design of Functional Materials(ICQD) Hefei National Research Center for Physical Sciences at the MicroscaleUniversity of Science and Technology of ChinaHefei 230026China Hefei National Laboratory University of Science and Technology of ChinaHefei 230088China

For conductors in the ballistic regime, electron-boundary scattering at the sample edge plays a dominant role in determining the transport performance, giving rise to many intriguing phenomena like low-field negative magnetoresistance effect. We systematically investigate the magneto-transport behaviors of BN-encapsulated graphene devices with narrow channel width W, wherein the bulk mean free path Lmfp can be very large and highly tunable. By comparing the magnetoresistance features and the amplitude of Lmfp in a large parameter space of temperature and carrier density, we reveal that the boundary-scattering-dominated negative magnetoresistance effect can still survive even when the ballistic ratio(Lmfp/W) is as low as 0.15. This striking value is much smaller than the expected value for achieving(quasi-) ballistic transport regime(Lmfp/W ≥ 1), and can be attributed to the ultra-low specularity of the sample edge of our graphene devices. These findings enrich our understanding of the effects of boundary scattering on channel transport, which is of vital importance for future designs of two-dimensional electronic devices with limited lateral sizes.

关键词： transport scattering boundary

Suitable Heat Transfer Model for Self-Similar Laminar boundary Layer in Power Law Fluids

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Journal of Thermal Science 2004年第2期13卷 150-154页

作者： Liancun ZHENG Xinxin ZHANG Jicheng HE Department of Mathematics and Mechanics University of Science and Technology BeijingBeijing 100083China Mechanical Engineering School University of Science and Technology BeijingBeijing 100083China Thermal Engineering Department Northeastern UniversityShenyang 110006China

The classical power law non-Newtonian fluids energy boundary layer equation is proved improper to describe the self-similar heat transfer. A theoretical analysis for momentum and energy boundary layer transfer behavior is made and the full similarity heat boundary layer equation is developed, which may be characterized by a power law relationship between shear stress and velocity gradient with the Falkner-Skan equation as a special case. Both analytical and numerical solutions are presented for momentum and energy boundary layer equations by using the similarity transformation and shooting technique and the associated transfer characteristics are discussed.

关键词： Power law fluid boundary layer heat transfer similarity solutions.

MHD boundary Layer Flow of Dilatant Fluid in a Divergent Channel with Suction or Blowing

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Chinese Physics Letters 2011年第8期28卷 175-178页

作者： Krishnendu Bhattacharyya G.C.Layek Department of Mathematics The University of BurdwanBurdwan-713104West BengalIndia

An analysis is carried out to study a steady magnetohydrodynamic(MHD)boundary layer flow of an electrically conducting incompressible power-law non-Newtonian fluid through a divergent *** channel walls are porous and subjected to either suction or blowing of equal magnitude of the same kind of fluid on both *** fluid is permeated by a magnetic field produced by electric current along the line of intersection of the channel *** governing partial differential equation is transformed into a self-similar nonlinear ordinary differential equation using similarity *** possibility of boundary layer flow in a divergent channel is analyzed with the power-law fluid *** analysis reveals that the boundary layer flow(without separation)is possible for the case of the dilatant fluid model subjected to suitable suction velocity applied through its porous walls,even in the absence of a magnetic ***,it is found that the boundary layer flow is possible even in the presence of blowing for a suitable value of the magnetic *** is found that the velocity increases with increasing values of the power-law index for the case of dilatant *** effects of suction/blowing and magnetic field on the velocity are shown graphically and discussed physically.

关键词： field walls boundary

A Lattice Boltzmann boundary Condition at Impermeable Boundaries

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Chinese Physics Letters 1997年第12期14卷 912-915页

作者： FANG Hai-ping LIN Zhi-fang TAO Rui-bao T.D.lee physics laboratory and department of physics fudan universityshanghai 200433

A hydrodynamic boundary condition for the lattice Boltzmann model at impermeable boundaries is *** boundary condition satisfies both the no-slip condition and the fluid conservation at boundary *** flow and Couette fl... 详细信息

关键词： boundary flow satis

A New Extrapolation Treatment for boundary Conditions in Lattice Boltzmann Method

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Chinese Physics Letters 2013年第9期30卷 89-93页

作者： WANG Zheng-Dao YANG Jian-Fei WEI Yi-Kun QIAN Yue-Hong Shanghai Institute of Applied Mathematics and Mechanics Shanghai UniversityShanghai 200072 Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai 200072 Shanghai Program for Innovative Research Team in Universities Shanghai 200072 Faculty of Mechanical Engineering and Automatic Zhejiang Sci-Tech UniversityHangzhou 310018 Department of Mechanical and Aerospace Enigineering UC IrvineCA 92617USA

The lattice Boltzmann method is widely used in solving hydrodynamics for various *** accuracy of the extrapolation method for boundary conditions and Mei’s method for curved boundary is not high *** propose a modified extrapolation method for boundary *** simulations conform the higher accuracy and stability compared with the other methods.

关键词： conditions methods boundary

GRAIN boundary CHARACTER DISTRIBUTION, TEXTURE AND SUPERPLASTIC DEFORMATION BEHAVIOR OF AN Al-Li ALLOY

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中国有色金属学会会刊：英文版 1999年第1期9卷 84-87页

作者： Zhang, Baojin Zeng, Meiguang Niu, Xuejun Ge, Shaoping Northeastern Univ Shenyang China

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关键词： aluminum lithium alloy grain boundary character distribution recrystallization texture superplasticity