检索结果-南通市图书馆

Development of SOM combustion model for Reynolds-averaged and large-eddy simulation of turbulent combustion and its validation by DNS

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2008年第8期51卷 1073-1086页

作者： ZHOU LiXing Department of engineering mechanics,{2., beijing 100084, China Department of engineering mechanics Tsinghua University Beijing 100084 China

The derivation and closure methods of the second-order moment (SOM) combus- tion model are proposed. The application of this model to Reynolds averaged (RANS) and large-eddy simulation (LES) of turbulent swirling diffusion combustion, jet diffusion combustion, and bluff-body stabilized premixed combustion is sum- marized. It is indicated that the SOM model is much better than the eddy-beak-up (EBU) and presumed PDF models widely used in commercial software and engi- neering. The SOM modeling results are close to those obtained using the most accurate but much more complex PDF equation model. Moreover, it can save much more computation time than the PDF equation model. Finally, the SOM model is validated by the direct numerical simulation (DNS) of turbulent reacting channel flows.

关键词： turbulent combustion second-order moment model Reynolds averaged simulation large-eddy simulation

Application and Comparison of Two SGS Models in Large Eddy Simulation of FreeTurbulent Jet Flow

在线全文

学校读者我要写书评

暂无评论

Communications in Nonlinear Science and Numerical Simulation 1999年第1期4卷 12-19页

作者： Hong YAN and Mingde SU (Department of engineering mechanics,{2., beijing 100084, China) Department of engineering mechanics Tsinghua University Beijing 100084 China

Large eddy simulations of spatially evolved turbulent round jets were presented. The two SGS models called the standard Smagorinsky’s eddy viscosity model and the non-eddy viscosity stimulated small scale(SSS) model developed by Shah & Ferziger were applied. The Reynolds number of the flow was taken as 10000 based on the orifice diameter and the axial velocity in the orifice. The comparison between these two models showed that the standard Smagorinsky’s viscosity model with Smagorinsky’s constant of 0.1 underestimated the turbulent intensity, while the SSS model showed a better agreement with the experiment. Also the SSS model was used to investigate the development of vortex. The convective boundary condition at the outflow boundary was adopted to ensure less effect of noise on the upstream.

关键词： stimulated small scale model smagorinsky’s eddy viscosity model Round jet, Large eddy simulation

Mechanism and control of convective heat transfer——Coordination of velocity and heat flow fields

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2001年第7期46卷 596-599页

作者： QUO ZengyuanDepartment of engineering mechanics,{2., beijing 100084, China Department of engineering mechanics Tsinghua University Beijing 100084 China

A second look has been given at the mechanism of convective heat transfer based on the analogy between convection and conduction with heat sources. The strength of convective heat transfer depends not only on the fluid velocity and fluid properties, but also on the coordination of fluid velocity and heat flow fields. Hence, based on the included angle of velocity and temperature gradient vectors, the presence of fluid motion may enhance or reduce heat transfer. With this concept, the known heat transfer phenomena may be understood in a deeper way. More important is that some novel approaches of heat transfer control can be developed.

关键词： convective heat transfer coordination heat transfer enhancement.

LARGE DEFLECTION THEORY OF NANOBEAMS

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2010年第5期23卷 394-399页

作者： Dujuan Zeng Quanshui Zheng 1(Department of engineering mechanics,{2. university,beijing 100084,China) [a] Department of engineering mechanics Tsinghua University Beijing 100084 China

One-dimensional nanostructured materials are often used as beams in many applications such as ultrahigh-frequency resonators and ultrasensitive sensors. Compared with usual macroscopic beams, nanobeams have much higher surface/volume ratios so that their surface energies may play a significant role. Besides, they often bear large deflections due to their typically large slenderness ratios and larger elastic ranges. There is, however, lack of a theory that takes into account of both the above two features owned by nanobeams. In this paper, we present such a theory and give applied examples to show that surface energy and large deflection may individually or jointly have notable effects.

关键词： nanobeam surface energy large deflection

CONSERVATION OF THREE-POINT COMPACT SCHEMES ON SINGLE AND MULTIBLOCK PATCHED GRIDS FOR HYPERBOLIC PROBLEMS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2003年第3期21卷 383-400页

作者： Zi-niu Wu (Department of engineering mechanics,{2., beijing 100084, China) Department of engineering mechanics Tsinghua University 北京 100084

For nonlinear hyperbolic problems, conservation of the numerical scheme is important for convergence to the correct weak solutions. In this paper the conservation of the well-known compact scheme up to fourth order of accuracy on a single and uniform grid is studied, and a conservative interface treatment is derived for compact schemes on patched grids. For a pure initial value problem, the compact scheme is shown to be equivalent to a scheme in the usual conservative form. For the case of a mixed initial boundary value problem, the compact scheme is conservative only if the rounding errors are small enough. For a patched grid interface, a conservative interface condition useful for mesh refinement and for parallel computation is derived and its order of local accuracy is analyzed.

关键词： Conservation Compact scheme Uniform grid Multiblock patched grid.

ARNOLDI REDUCTION ALGORITHM FOR LARGE SCALE GYROSCOPIC EIGENVALUE PROBLEM

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 1996年第2期9卷 95-103页

作者： Zheng Zhaochang Ren Gexue, Department of engineering mechanics,{2., beijing 100084 TSING HUA UNIV DEPT ENGN MECH BEIJING 100084 PEOPLES R CHINA

Based on Arnoldi's method, a version of generalized Arnoldi algorithm has been developed for the reduction of gyroscopic eigenvalue problems. By utilizing the skew symmetry of system matrix, a very simple recurrence scheme, named gyroscopic Arnoldi reduction algorithm has been obtained, which is even simpler than the Lanczos algorithm for symmetric eigenvalue problems. The complex number computation is completely avoided. A restart technique is used to enable the reduction algorithm to have iterative characteristics. It has been found that the restart technique is not only effective for the convergence of multiple eigenvalues but it also furnishes the reduction algorithm with a technique to check and compute missed eigenvalues. By combining it with the restart technique, the algorithm is made practical for large-scale gyroscopic eigenvalue problems. Numerical examples are given to demonstrate the effectiveness of the method proposed.

关键词： gyroscopic eigenvalue problem skew symmetry Arnoldi reduction algorithm restart technique

NUMERICAL DISSIPATION FOR THREE-POINT DIFFERENCE SCHEMES TO HYPERBOLIC EQUATIONS WITH UNEVEN MESHES

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2003年第4期21卷 519-534页

作者： Zi-niu Wu(Department of engineering mechanics,{2., beijing 100084, China) Department of engineering mechanics Tsinghua University Beijing 100084 China

The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. The numerical dissipation due to these interfaces is studied here for three-point difference approximations of a hyperbolic equation. It will be shown that if the wave moves in the fine-to-coarse direction then the dissipation is positive (stabilizing), and if the wave moves in the coarse-to-fine direction then the dissipation is negative (destabilizing).

关键词： Refined interfaces Numerical dissipation Three-point difference approxima-tion Hyperbolic equation.

Multiple time step molecular dynamics simulation for interaction between dislocations and grain boundaries

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2005年第4期21卷 371-379页

作者： X.Y.Li W.Yang Department of engineering mechanics,{2. university,beijing 100084.China Department of engineering mechanics Tsinghua University Beijing 100084 China

A multiple time step algorithm, called reversible reference system propagator algorithm, is introduced for the long time molecular dynamics simulation. In contrast to the conventional algorithms, the multiple time method has better convergence, stability and efficiency. The method is validated by simulating free relaxation and the hypervelocity impact of nano-clusters. The time efficiency of the multiple time step method enables us to investigate the long time interaction between lattice dislocations and low-angle grain boundaries.

关键词： Multiple time step Molecular dynamics ,Dislocation Grain boundary

Computational fluid dynamics modeling and hemolysis analysis of axial blood pumps with various impeller structures

在线全文

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2006年第9期16卷 993-997页

作者： XIA Dongdong, ZHAO Chunzhang, ZHANG Xiwen and BAI Jing ( Department of Biomedical engineering, tsinghua university,{2., China Department of engineering mechanics, tsinghua university,{2., China) [a]Department of Biomedical engineering Tsinghua University Beijing China [b]Department of engineering mechanics Tsinghua University Beijing China

The flow fields in the blood pump were analyzed three- dimensionally using computational fluid dynamics (CFD). Hemolysis of the pump was calculated based on the changes in shear stress and related exposure times along the particle trace lines using a forward Euler approach. In this "way, how different impeller structures and rotational speeds affect the hemolysis was particularly acquired. As a result, impeller with long-short alternant vanes behaved best in hemolysis property and can be utilized to axial blood pumps development and design.

关键词： axial blood pump computational fluid dynamics hemolysis.