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41.
Kazem Hejranfar Vahid Esfahanian Mehdi Najafi 《Journal of computational physics》2009,228(11):3936-3972
The purpose of this paper is to study and identify suitable outflow boundary conditions for the numerical simulation of viscous supersonic/hypersonic flow over blunt bodies, governed by the compressible Navier–Stokes equations, with an emphasis motivated primarily by the use of spectral methods without any filtering. The subsonic/supersonic composition of the outflow boundary requires a dual boundary treatment for well-posedness. All compatibility relations, modified to undertake the hyperbolic/parabolic behaviour of the governing equations, are used for the supersonic part of the outflow. Regarding the unknown downstream information in the subsonic region, different subsonic outflow conditions in the sense of the viscous blunt-body problem are examined. A verification procedure is conducted to make out the distinctive effect of each outflow condition on the solution. Detailed comparisons are performed to examine the accuracy and performance of the outflow conditions considered for two model geometries of different surface curvature variations. Numerical simulations indicate a noticeable influence of pressure from subsonic portion to supersonic portion of the boundary layer. It is demonstrated that two approaches for imposing subsonic outflow conditions namely (1) extrapolating all flow variables and (2) extrapolation of pressure along with using proper compatibility relations are more suitable than the others for accurate numerical simulation of viscous high-speed flows over blunt bodies using spectral collocation methods. 相似文献
42.
Myoungjean Bae Shangkun Weng 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2018,35(1):161-186
We address the structural stability of 3-D axisymmetric subsonic flows with nonzero swirl for the steady compressible Euler–Poisson system in a cylinder supplemented with non-small boundary data. A special Helmholtz decomposition of the velocity field is introduced for 3-D axisymmetric flow with a nonzero swirl (=?angular momentum density) component. With the newly introduced decomposition, a quasilinear elliptic system of second order is derived from the elliptic modes in Euler–Poisson system for subsonic flows. Due to the nonzero swirl, the main difficulties lie in the solvability of a singular elliptic equation which concerns the angular component of the vorticity in its cylindrical representation, and in analysis of streamlines near the axis . 相似文献
43.
Velocity effect and critical velocity are incorporated into the average space gap cellular automaton model [J.F. Tian, et al., Phys. A 391 (2012) 3129], which was able to reproduce many spatiotemporal dynamics reported by the three-phase theory except the synchronized outflow of wide moving jams. The physics of traffic breakdown has been explained. Various congested patterns induced by the on-ramp are reproduced. It is shown that the occurrence of synchronized outflow, free outflow of wide moving jams is closely related with drivers time delay in acceleration at the downstream jam front and the critical velocity, respectively. 相似文献
44.
45.
《Comptes Rendus Mecanique》2017,345(8):581-594
Fly higher, faster, preserve the life of test pilots and passengers, many challenges faced by man since the dawn of the twentieth century, with aviation pioneers. Contemporary of the first aerial exploits, wind tunnels, artificially recreating conditions encountered during the flight, have powerfully contributed to the progress of aeronautics.But the use of wind tunnels is not limited to aviation. The research for better performance, coupled with concern for energy saving, encourages manufacturers of ground vehicles to perform aerodynamic tests. Buildings and bridge structures are also concerned.This article deals principally with the wind tunnels built at ONERA during the last century. Somme wind tunnels outside ONERA, even outside France, are also evocated when their characteristics do not exist at ONERA. 相似文献
46.
The 12CO (J=1-0), 13CO (J=1-0) and C18O (J=1-0) emissions in 9 massive star forming regions, which are believed to be at different stages of massive star formation,
were mapped with the 13.7 m millimeter wave telescope at Qinghai Station of Purple Mountain Observatory. Of the observed 9
sources, 13CO cores were detected in seven of them, and C18O cores in five of them. And only two sources associated with C18O cores and H2O masers showed the extended structures and strong outflows. This is the first detection of outflow associated with IRAS 22566+5828
in the observing field of S152/S153. The physical parameters of cores and outflows for these sources, derived from Local Thermal
Equilibrium (LTE) analysis, are presented. These observing results suggest that the C18O cores will only appear when the gas density is high enough and the probability to have an outflow is very high when the
clumps show the C18O and H2O maser simultaneously. 相似文献
47.
V. Ricci A. Shukla V. B. Chalivendra K. H. Lee 《Theoretical and Applied Fracture Mechanics》2003,39(2):143-161
An experimental study has been conducted in which strain fields were used to investigate the behavior of subsonic crack propagation along the interface of an isotropic–orthotropic bimaterial system. Strain field equations were developed from available field equations and critically evaluated in a parametric study to identify optimum strain gage location and orientation. Bimaterial specimens were prepared with PSM-1 polycarbonate and Scotchply® 1002 unidirectional, glass-fiber-reinforced, epoxy composite. Dynamic experiments were conducted using these specimens with strain gages mounted on the composite half to obtain values of the dynamic complex stress intensity factor, K=K1+iK2, in the region of the crack tip while photoelasticity was used on the PSM-1 half. Results show that the trend and magnitude of K obtained using strain gages compare favorably with those obtained using photoelasticity. 相似文献
48.
A variational method for solving directly the full steady Euler equations is presented. This method is based on both Newton's linearization and a least squares formulation. The validity of the Euler model and boundary conditions to capture the vortex sheet is discussed. A finite element approximation of the groups of conservative variables is described and results are given for 3D subsonic flows as well as supersonic flows past a flat plate at high angle of attack. 相似文献
49.
B. K. Shivamoggi 《Proceedings Mathematical Sciences》1978,87(5):107-112
In an effort to shed further light upon the nature of “supersonic” disturbances as distinct from that of ‘subsonic’ disturbances
in parallel compressible flows, this paper makes an investigation of the stability characteristics of the surface waves generated
in a liquid layer adjacent to a high-speed gas-stream. It turns out that the nature of the surface waves generated in the
liquid layer depends markedly upon the type of disturbances present in the high-speed gas-stream. For the case of ‘subsonic’
disturbances it is shown that the energy transfer from the gas stream to the surface waves is contributed predominantly by
the Fourier component of the normal gas-pressure force-field in phase with the slope of the wavy surface. For the case of
‘supersonic’ disturbances, this energy transfer is shown to be predominantly due to the component of the pressure-field in
phase with the surface-wave displacement and is related to the presence of travelling periodic waves in the gas-stream—this
energy transfer is shown to promote always the growth of the surface waves. 相似文献
50.
For incompressible Navier–Stokes equations in primitive variables, a method of setting absorbing outflow boundary conditions on an artificial boundary is considered. The advection equations used on the outflow boundary are convenient for finite difference (FD) methods, where a weak formulation of a problem is inapplicable. An unsteady viscous incompressible Navier–Stokes flow in a channel with a moving damper is modeled. An accurate comparison and analysis of numerical and mechanical situations are carried out for a variety of boundary conditions and Reynolds numbers. The proposed outflow conditions provide that the problem with Dirichlet boundary conditions should be solved on each time step. 相似文献