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Computations of wall distances by solving a transport equation

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Applied Mathematics and Mechanics(English Edition) 2011年第2期32卷 141-150页

作者：徐晶磊阎超范晶晶 National laboratory for computational Fluid dynamics Beihang University

Computations of wall distances still play a key role in modern turbulence modeling. Motivated by the expense involved in the computation, an approach solving partial differential equations is considered. An Euler-like transport equation is proposed based on the Eikonal equation. Thus, the efficient algorithms and code components developed for solving transport equations such as Euler and Navier-Stokes equations can be reused. This article provides a detailed implementation of the transport equation in the Cartesian coordinates based on the code of computational fluid dynamics for missiles （MI- CFD） of Beihang University. The transport equation is robust and rapidly convergent by the implicit lower-upper symmetric Gauss-Seidel （LUSGS） time advancement and upwind spatial discretization. Geometric derivatives must also be upwind determined to ensure accuracy. Special treatments on initial and boundary conditions are discussed. This distance solving approach is successfully applied on several complex geometries with 1-1 blocking or overset grids.

关键词： wall distance numerical simulation overset grid

Simulation of three-dimensional nonideal MHD flow at low magnetic Reynolds number

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Science China(Technological Sciences) 2009年第12期52卷 3690-3697页

作者： LEE ChunHian National laboratory for computational Fluid dynamics Beihang University

A numerical procedure based on a five-wave model associated with non-ideal,low magnetic Reynolds number magnetohydrodynamic(MHD)flows was *** is composed of an entropy conditioned scheme for solving the non-homogeneous Navier-Stokes equations,in conjunction with an SOR method for solving the elliptic equation governing the electrical potential of flow *** validate the developed procedure,two different test cases were used which included MHD Rayleigh problem and MHD Hartmann *** simulations were performed under the assumption of low magnetic Reynolds *** simulated results were found to be in good agreement with the closed form analytical solutions deduced in the present study,showing that the present algorithm could simulate engineering MHD flow at low magnetic Reynolds number *** the end,a flow field between a pair of segmented electrodes in a three dimensional MHD channel was simulated using the present algorithm with and without including Hall *** the introduction of Hall effects,no distortion was observed in the current and potential *** taking the Hall effects into account,the potential lines distorted and clustered at the upstream and downstream edges of the cathode and anode,respectively.

关键词： magnetohydrodynamics(MHD) numerical simulation MHD Rayleigh flow MHD Hartmann flow MHD generator

An implicit algorithm based on iterative modified approximate factorization method coupling with characteristic boundary conditions for solving subsonic viscous flows

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Science China(Physics,Mechanics & Astronomy) 2013年第6期56卷 1187-1208页

作者： LEE XuZhi LEE ChunHian National laboratory for computational Fluid dynamics Beihang University

An algorithm composed of an iterative modified approximate factorization(MAF(k)) method with Navier-Stokes characteristic boundary conditions(NSCBC) is proposed for solving subsonic viscous flows.A transformation on the matrix equation in MAF(k) is made in order to impose the implicit boundary conditions *** be in consistent with the implicit solver for the interior domain,an implicit scheme for NSCBC is *** performance of the developed algorithm is investigated using spatially evolving zero pressure gradient boundary layer over a flat plate and a wall jet mixing with a cross flow over a flat plate with a square hole as the test *** numerical results are compared to the existing experimental datasets and a number of general correlations,together with other available numerical solutions,which demonstrate that the developed algorithm possesses promising capacity for simulating the subsonic viscous flows with large CFL number.

关键词： iterative modified approximate factorization Navier-Stokes characteristic boundary conditions subsonic viscous flow

Quantification of parametric uncertainty in c-Reh model for typical flat plate and airfoil transitional flows

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Chinese Journal of Aeronautics 2023年第4期36卷 237-251页

作者： Ziming SONG Zaijie LIU Jiachen LU Chao YAN National Key laboratory of computational Fluid dynamics Beihang UniversityBeijing 100191China

Owing to the lack of physical knowledge of boundary layer transition,the c-Reh transi-tion model introduces closure parameters,which increase the uncertainty of transition *** objective of this work is to quantify the uncertainties of closure parameters in the quantities of interests and identify the key *** six closure parameters in the uncertainty intervals are used as input variables,and the uncertainties of the output results are propagated by a stochas-tic expansion based on the point-collocation nonintrusive polynomial chaos *** relative contribution of each parameter to uncertainty is evaluated by the Sobol *** computational cases include natural and bypass transitional flows on zero-pressure-gradient flat plates,and sub-sonic and transonic flows around *** most cases,c_(e2),c_(a2),and c_(a1)dominate the uncertainty,and the influence of r ht is also significant when the history effects of flow are *** contri-bution of parameters in airfoils is more complex than that in flat *** transonic airfoil case shows that flow separation dramatically changes the distribution of Sobol indices,which poses a challenge to the accurate prediction of ***,c_(e2)and c_(a2)are the key parameters of the c-Reh model.

关键词： Airfoil transition Closure parameters Sensitivity analysis Uncertainty analysis c-Reh transition model

The stability of rolling motion of hypersonic vehicles with slender configuration under pitching maneuvering

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Science China(Physics,Mechanics & Astronomy) 2015年第6期58卷 86-94页

作者： YE YouDa TIAN Hao ZHANG XiaFeng State Key laboratory of Aerodynamics China Aerodynamic Research and Development Center National laboratory for computational Fluid dynamics

The configurations of near space hypersonic flying vehicles are considerably different from those of conventional *** configurations are relatively slender;hence their moment of inertia around the longitudinal axis is much smaller than those around the other two axes,resulting in strong coupling of rotations around the three ***,the stability analysis of rolling motion for such flying vehicles is more complicated than those for conventional aircrafts,and there is no available result of stability analysis which can readily be applied to such *** paper is mainly concerned with the stated *** the practical situation,our investigation is targeted a slightly simpler problem,namely the rolling stability of flying vehicle under known pitching *** stability criterion of rolling motion is obtained with and without lateral *** also conducted numerical simulation for the pitching-rolling coupled motions of flying vehicles by solving Navier-Stokes equations coupled with dynamic equations of *** results of simulation agree well with those of theoretical analysis and experiments.

关键词： stability rolling motion pitching motion hypersonic flying vehicle

Enhancement and Application of Overset Grid Assembly

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Chinese Journal of Aeronautics 2010年第6期23卷 631-638页

作者： Fan Jingjing Yan Chao National laboratory of computational Fluid dynamics Beijing University of Aeronautics and AstronauticsBeijing 100191China

In this article, the overset grid assembly method is improved to efficiently solve several critical problems that occur when applying overset grids to the complicated geometries and moving body. First, instead of using the two-step searching (i.e. cut and paste), a single-step searching method based on the grid cell size is proposed to modify holes and optimize the grid overlapping automatically. Second, discrepancies between the wall surface representations, where the grids overlap, are handled by introducing the wall's normal directions to the hole-map and projecting the interpolated points on the recipient mesh into the donor mesh. Finally, the dynamic overset method is modified to address the complex moving body problem. At every time step, the initial hole surface of the previous time step is dynamically adjusted to accomplish hole cutting and avoid the time consuming hole-map procedure. Numerical experiments show that the enhanced overset grid assembly method obtains satisfactory results.

关键词： overset grid hole-map hole-surface optimization surface grid overset dynamic overset

How does the rarefaction of the air affect hypersonic vehicles

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Acta Mechanica Sinica 2021年第1期37卷 18-19,I0002页

作者： Youda Ye National laboratory for computational Fluid dynamics Beijing100086China

The scope,physical concept,and mathematical model for describing how the rarefaction of the air affects on hypersonic flows have been discussed.A new method,namely the data improved Naive-Stroke(DiNS)model,was proposed for the computation of hypersonic shear flows around vehicles flying at altitude of 30-100 *** of the new continuum method has also been done.

关键词： hypersonic flows rarefaction

Towards an entropy-based detached-eddy simulation

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Science China(Physics,Mechanics & Astronomy) 2013年第10期56卷 1970-1980页

作者： ZHAO Rui YAN Chao LI XinLiang KONG WeiXuan National laboratory for computational Fluid dynamics Beijing University of Aeronautics and Astronautics Key laboratory of High Temperature Gas dynamics Institute of Mechanics Chinese Academy of Sciences

A concept of entropy increment ratio （ s- ） is introduced for compressible turbulence simulation through a series of direct nu- merical simulations （DNS）. s- represents the dissipation rate per unit mechanical energy with the benefit of independence of freestream Mach numbers. Based on this feature, we construct the shielding function f, to describe the boundary layer region and propose an entropy-based detached-eddy simulation method （SDES）. This approach follows the spirit of delayed de- tached-eddy simulation （DDES） proposed by Spalart et al. in 2005, but it exhibits much better behavior after their performanc- es are compared in the following flows, namely, pure attached flow with thick boundary layer （a supersonic fiat-plate flow with high Reynolds number）, fully separated flow （the supersonic base flow）, and separated-reattached flow （the supersonic cavity-ramp flow）. The Reynolds-averaged Navier-Stokes （RANS） resolved region is reliably preserved and the modeled stress depletion （MSD） phenomenon which is inherent in DES and DDES is partly alleviated. Moreover, this new hybrid strategy is simple and general, making it applicable to other models related to the boundary layer predictions.

关键词： hybrid RANS/LES detached-eddy simulation turbulence compressible flows entropy

Numerical simulation of sand load applied on high-speed train in sand environment

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Journal of Central South University 2017年第2期24卷 442-447页

作者：王田天蒋崇文高振勋李椿萱 National laboratory for computational Fluid dynamics School of Aeronautic Science and Engineering Beihang University Beijing 100191 China

High-speed train running in the sand environment is different from the general environment. In the former situation, there will be sand load applied on high-speed train(SLAHT) caused by sand particles hitting train surface. This will have a great impact on the train stability, running drag and surface corrosion. Numerical simulation method of SLAHT in sand environment is studied. The velocity and mass flow rate models of saltation and suspension sand particles and the calculation model of SLAHT caused by sand particles hitting train surface are established. The discrete phase method is adopted for numerical simulating the process of saltation and suspension sand particles moving to train surface and generating sand load. By comparison with the field tests, the numerical simulation reliability is analysed. The theoretical formula of SLAHT changing with cross-wind and train speed is proposed. SLAHT changing law is analyzed. Research results indicate that SLAHT changing with cross-wind and train speed is a quadratic relationship. When train speed is constant, SLAHT increases quadratically with cross-wind speed improvement. When cross-wind speed is constant, SLAHT increases quadratically with train speed improvement.

关键词： sand environment train saltation suspension sand load numerical simulation