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The Effects of Limiters on High Resolution Computations of Hypersonic Flows over Bodies with Complex Shapes

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Communications in Nonlinear Science and Numerical Simulation 1998年第2期3卷 30-35页

作者： Bo ZHENG and Chun Hian LEE (national laboratory for computational fluid dynamics, beijing university of Aeronautics & Astronautics, beijing 100083, china) national laboratory for computational fluid dynamics Beijing University of Aeronautics & Astronautics Beijing 100083 China

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关键词： TVD scheme hypersonic flows entropy correction function limiter

Study on the unified algorithm for three-dimensional complex problems covering various flow regimes using Boltzmann model equation

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Science china(Physics,Mechanics & Astronomy) 2009年第1期52卷 124-138页

作者： LI ZhiHui1,2 & ZHANG HanXin1 1 national laboratory for computational fluid dynamics, beijing 100083, china 2 china Aerodynamics Research and Development Center, Hypervelocity Aerodynamics Institute, Mianyang 621000, china national laboratory for computational fluid dynamics Beijing China china Aerodynamics Research and Development Center Hypervelocity Aerodynamics Institute Mianyang China

The Boltzmann simplified velocity distribution function equation describing the gas transfer phenomena from various flow regimes will be explored and solved numerically in this study. The discrete velocity ordinate method of the gas kinetic theory is studied and applied to simulate the complex multi-scale flows. Based on the uncoupling technique on molecular movement and colliding in the DSMC method, the gas-kinetic finite difference scheme is constructed to directly solve the discrete velocity distribution functions by extending and applying the unsteady time-splitting method from computational fluid dynamics. The Gauss-type discrete velocity numerical quadrature technique for different Mach number flows is developed to evaluate the macroscopic flow parameters in the physical space. As a result, the gas-kinetic numerical algorithm is established to study the three-dimensional complex flows from rarefied transition to continuum regimes. The parallel strategy adapted to the gas-kinetic numerical algorithm is investigated by analyzing the inner parallel degree of the algorithm, and then the HPF parallel processing program is developed. To test the reliability of the present gas-kinetic numerical method, the three-dimensional complex flows around sphere and spacecraft shape with various Knudsen numbers are simulated by HPF parallel computing. The computational results are found in high resolution of the flow fields and good agreement with the theoretical and experimental data. The computing practice has confirmed that the present gas-kinetic algorithm probably provides a promising approach to resolve the hypersonic aerothermodynamic problems with the complete spectrum of flow regimes from the gas-kinetic point of view of solving the Boltzmann model equation.

关键词： Boltzmann model equation kinetic theory velocity distribution function discrete velocity ordinate technique hypersonic flow parallel computing numerical methods

Stabilization control of a bumblebee in hovering and forward flight

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Acta Mechanica Sinica 2009年第1期25卷 13-21页

作者： Yan Xiong Mao Sun Institute of fluid Mechanics, beihang university,beijing 100083, china Institute of fluid Mechanics Beihang University Beijing China

Our previous study shows that the hovering and forward flight of a bumblebee do not have inherent stability （passive stability）. But the bumblebees are observed to fly stably. Stabilization control must have been applied. In this study, we investigate the longitudinal stabilization control of the bumblebee. The method of computational fluid dynamics is used to compute the control derivatives and the techniques of eigenvalue and eigenvector analysis and modal decomposition are used for solving the equations of motion. Controllability analysis shows that at all flight speeds considered, although inherently unstable, the flight is controllable. By feedbacking the state variables, i.e. vertical and horizontal velocities, pitching rate and pitch angle （which can be measured by the sensory system of the insect）, to produce changes in stroke angle and angle of attack of the wings, the flight can be stabilized, explaining why the bumblebees can fly stably even if they are passively unstable.

关键词： Insect - Hovering and forward flight - Stabilization control Navier-Stokes simulation Modal analysis

A computational trust model for access control in P2P

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Science china(Information Sciences) 2010年第5期53卷 896-910页

作者： LANG Bo State Key laboratory of Software Development Environment, beihang university, beijing 100191, china State Key laboratory of Software Development Environment Beihang University Beijing China

Trust brings a new method for building scalable and fine-grained access control mechanism in P2P systems. The quantificational expression of trust and the calculation of trust in a trust network are the basis of trust degree based access control. In this paper, the properties of trust is analyzed by referring to the fruits from social science; the semantics of trust in the context of access control is described, and a trust degree based access control model named TDBAC is introduced. Basing on the properties and semantics of trust, a computational trust model which includes a multilevel comprehensive evaluation method for expressing direct trust and calculators for computing recommended trust is put forward. To compute trust in a trust network, an algorithm that transforms a trust network to a computable expression is given. The algorithm simplifies the computation process and is also flexible.

关键词： trust management access control trust degree based access control computational trust model trust graph expression

A non-flux-splitting WENO scheme with low numerical dissipation

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Science china(Technological Sciences) 2010年第4期53卷 3365-3378页

作者： KANG Lei & Lee ChunHian national laboratory for CFD, beihang university, beijing 100191, china national laboratory for CFD Beihang University Beijing China

A WENO scheme without implementing the flux-splitting procedure is developed in the present paper. The scheme is deduced by taking the optimized coefficients, originally constant in any flux-splitting WENO scheme, to vary with respect to eigenvalues in the characteristic space. As a result, the weights are associated with both the eigenvalues and the smoothness measurements. The scheme is formulated to avoid the implementing of the flux-splitting procedure via computation of the weighs of WENO stencils, and is capable of reducing the numerical dissipation. Numerical experiments show that the new scheme is less dissipative than the WENO scheme with flux-splitting, and possesses higher resolution using the same grid mesh. Computations of the test cases also demonstrate a comparatively higher computational efficiency of the new scheme. Especially, for problems involving shocks, strong shear and long time evolution, the solutions computed by the presently developed scheme with no flux-splitting and the other existing methods with flux-splitting differ remarkably from each other, and the new scheme is proven to be an effective way for controlling the numerical dissipation and retaining the real effects of the physical viscosity.

关键词： flux-splitting WENO scheme numerical dissipation

Effects of flexibility on aerodynamic performance of delta wings with different sweep angles

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Science china(Physics,Mechanics & Astronomy) 2010年第5期53卷 915-922页

作者： LIU Yang,ZUO LinXuan & WANG JinJun Institute of fluid Mechanics,beijing university of Aeronautics and Astronautics and fluid Mechanics Key laboratory,Ministry of Education,beijing 100191,china Institute of fluid Mechanics Beijing University of Aeronautics and Astronautics and Fluid Mechanics Key Laboratory Ministry of Education Beijing China

Force measurement and surface oil flow visualization experiments were conducted in a wind tunnel to investigate the effects of flexibility on aerodynamic performance of delta wings with different sweep *** experimental results indicate that the maximum lift coefficient is increased and the stall angle is delayed as the sweep angle increases for both rigid and flexible *** is also found that the maximum lift coefficients of the flexible wings with a sweep angle from 35° to 50° are higher than those of the rigid *** increment of the maximum lift coefficient in particular achieves 32.9% compared with the case without lift enhancement for the 40° flexible delta ***,the surface oil flow visualization experiments show that the stall of the flexible wing of the moderate low sweep angle is accompanied by helical flow structure,while the vortex bursting appears on the corresponding rigid wing.

关键词： delta wing wing flexibility aerodynamics sweep angle

Physical analysis and numerical simulation for the dynamic behaviour of vehicles in pitching oscillations or rocking motions

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Science china(Technological Sciences) 2007年第4期50卷 385-401页

作者： ZHANG HanXin1,2,3, ZHANG Zhao1,3, YUAN XianXu1,2, LIU Wei1, XIE YuFei1,2 & YE YouDa1,2 1 china Aerodynamics Research and Development Center, Mianyang 621000, china 2 national laboratory for computational fluid dynamics, beijing university of Aeronautics and Astronautics, beijing 100083, china 3 School of Aerospace, Tsinghua university, beijing 100084, china china Aerodynamics Research and Development Center Mianyan China national laboratory for computational fluid dynamics Beijing University of Aeronautics and Astronautics Beijing China School of Aerospace Tsinghua University Beijing China

Analytical methods of nonlinear dynamics and numerical simulations for the cou-pling equations of Navier-Stokes and flight mechanics are used to study the dynamic behaviour of pitching motions of reentry capsules with the variation of Mach number, and rocking motions of swept wings with the variation of angle of attack. Conditions under which the dynamic instability, Hopf bifurcation and saddle-node bifurcation occur are obtained. The node-saddle-node topological structure in the phase portrait, i.e. the state of bi-attractors (attracting basins) is described. The evolving process of dynamic behaviour and flow fields are given. The theories are compared with some numerical simulations conducted by the authors. Besides, some verifiable experi-mental results are cited. The agreement between them is very well.

关键词： physical analysis numerical simulation pitching oscillation rocking motion bifurcation

Multi-scale sparse feature point correspondence by graph cuts

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Science china(Information Sciences) 2010年第6期53卷 1224-1232页

作者： ZHANG Hong 1 , MU Ying 1 , YOU YuHu 2 & LI JunWei 3 1 Image Processing Center, beihang university, beijing 100191, china 2 beijing Research Institute of Special Electromechanical Technology, beijing 100012, china 3 national Key laboratory on Optical Features of Environment and Target, beijing 100854, china Image Processing Center Beihang University Beijing China beijing Research Institute of Special Electromechanical Technology Beijing China national Key laboratory on Optical Features of Environment and Target Beijing China

This paper presents a global stereo sparse matching technique based on graph cut theory to obtain accurate correspondence of stereo point pair in vision measurement ***, in order to obtain accurate location of feature points, a new multi-scale corner detection algorithm is proposed where wavelet coefficients are used to determine feature points by calculating an auto-correlation matrix.A sparse graph is constructed based on the feature points according to the graph cut ***, the feature point correspondence problem is transformed into a labeling problem in the sparse graph which can be solved by energy ***-scale analysis is utilized to improve the precision of matching *** was found that the use of sparse feature points in the construction of the graph can lead to both a simple graph structure and a reduced computational *** was also found that node labeling in the graph can be performed using fewer disparity values instead of all disparity *** experimental results show that the new global stereo sparse matching technique can obtain more accurate results than the existing techniques.

关键词： multi-scale feature point extraction graph cut theory stereo correspondence sparse point matching

Study on flow behavior and structure over chined fuselage at high angle of attack

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Science china(Technological Sciences) 2010年第8期53卷 2057-2067页

作者： TIAN Wei,DENG XueYing ,WANG YanKui,FAN GuoLei&DONG Chao Ministry of Education Key laboratory of fluid Mechanics,beijing university of Aeronautics and Astronautics,beijing 100191,china Ministry of Education Key laboratory of fluid Mechanics Beijing University of Aeronautics and Astronautics Beijing China

A study of leeward vortex structure over chined fuselage and the effects of micro tip perturbation on its vortex flow have been carried out in wind tunnel experiments at Reynolds numbers from 1.26×105 to 5.04×105 with PIV and pressure measurement ***,the experiment results have proved that micro tip perturbation has no effects on the vortex flow and its aerodynamic characteristics over chined fuselage at high angle of attack,in which there are not any non-deterministic flow ***,the evolution of leeward vortex structure over chined fuselage along the axis of model can be divided into four flow regimes:linear conical developed regime,decay regime of leeward vortex intensity,asymmetric leeward vortex break down regime and completely break down *** a correlation between leeward vortex structure and sectional aerodynamic force was also revealed in the present ***,the experiment results show the behavior of leeward vortex core trajectories and zonal characteristics of leeward vortex structure with angles of ***,the experiment results of Reynolds number effect on the leeward vortex flow have further confirmed research conclusions from previous studies:the flows over chined fuselage at high angles of attack are insensitive to variation of Reynolds number,and there is a little effect on the secondary boundary layer separation and the suction peak induced by leeward vortex.

关键词： high angle of attack aerodynamics chined fuselage tip perturbation leeward vortex structure zonal characteristics