排序方式: 共有70条查询结果,搜索用时 15 毫秒
1.
A multigrid acceleration technique developed for solving the three-dimensional Navier–Stokes equations for subsonic/transonic flows has been extended to supersonic/hypersonic flows. An explicit multistage Runge–Kutta type of time-stepping scheme is used as the basic algorithm in conjunction with the multigrid scheme. Solutions have been obtained for a blunt conical frustum at Mach 6 to demonstrate the applicability of the multigrid scheme to high-speed flows. Computations have also been performed for a generic High-Speed Civil Transport configuration designed to cruise at Mach 3. These solutions demonstrate both the efficiency and accuracy of the present scheme for computing high-speed viscous flows over configurations of practical interest. 相似文献
2.
A numerical investigation for an axisymmetric hypersonic turbulent inlet flow field of a perfect gas is presented for a three-shock configuration consisting of a biconic and a cowl. An upwind parabolized Navier-Stokes solver based on Roe's scheme is used to compute an oncoming flow Mach numberM
=8, temperatureT
=216 K, and pressureP
=5.5293×103 N/m2. In order to assess the flow quantities, the interaction between shock and turbulence, and the inlet efficiency, three different flow calculations — laminar, turbulent with incompressible and compressible two-equationk- turbulence models — have been performed in this work.Computational results show that turbulence is markedly enhanced across an oblique shock with step-like increases in turbulence kinetic energy and dissipation rate. This enhancement is at the expense of the mean kinetic energy of the flow. Therefore, the velocity behind the shock is smaller in turbulent flow and hence the shock becomes stronger. The entropy increase through a shock is caused not only by the amplification of random molecular motion, but also by the enhancement of the chaotic turbulent flow motion. However, only the compressiblek- turbulence model can properly predict a decrease in turbulence length scale across a shock. Our numerical simulation reveals that the incompressiblek- turbulence model exaggerates the interaction between shock and turbulence with turbulence kinetic energy and dissipation rate remaining high and almost undissipated far beyond the shock region. It is shown that proper modeling of turbulence is essential for a realistic prediction of hypersonic inlet flowfield. The performed study shows that the viscous effect is not restricted in the boundary layer but extends into the main flow behind a shock wave. The loss of the available energy in the inlet performance therefore needs to be determined from the shock-turbulence interaction. The present study predicts that the inlet efficiency becomes relatively lower when turbulence is taken into account. 相似文献
3.
R.C. Mehta 《Shock Waves》2002,11(6):431-440
The pressure oscillations over a forward facing spike attached to an axisymmetric blunt body are simulated by solving time-dependent
compressible Navier–Stokes equations. The governing fluid flow equations are discretized in spatial coordinates employing
a finite volume approach which reduces the equations to semidiscretized ordinary differential equations. Temporal integration
is performed using the two-stage Runge–Kutta time stepping scheme. A global time step is used to obtain a time-accurate numerical
solution. The numerical computation is carried out for a freestream Mach number of 6.80 and for spike length to hemispherical
diameter ratios of 0.5, 1.0 and 2.0. The flow features around the spiked blunt body are characterized by a conical shock wave
emanating from the spike tip, a region of separated flow in front of the hemispherical cap, and the resulting reattachment
shock wave. Comparisons of the numerical results are made with the available experimental results, such as schlieren pictures
and the surface pressure distribution along the spiked blunt body. They are found to be in good agreement. Spectral analysis
of the computed pressure oscillations are performed employing fast Fourier transforms. The surface pressure oscillations over
the spike and phase plots exhibit a behaviour analogous to that of the Van der Pol equation for a self-sustained oscillatory
flow.
Received 28 February 2001 / Accepted 17 January 2002 相似文献
4.
We study the temporal evolution of the combustion flowfield established by the interaction of ram accelerator-type projectiles
with an explosive gas mixture accelerated to hypersonic speeds in an expansion tube. The Navier-Stokes equations for a chemically
reacting gas mixture are solved in a fully coupled manner using an implicit, time accurate algorithm. The solution procedure
is based on a spatially second order, total variation diminishing scheme and a temporally second order, variable-step, backward
differentiation formula method. The hydrogen-oxygen-argon chemistry is modeled with a 9-species, 19-step mechanism. The accuracy
of the solution method is first demonstrated by several benchmark calculations. Numerical simulations of expansion tube flowfields
are then presented for two different geometries: an axisymmetric projectile and a ram accelerator configuration. The development
of the shock-induced combustion process is followed. The temporal variations of the calculated thrust and drag forces on the
ram accelerator projectile are also presented. In the axisymmetric projectile case, which was designed to ensure combustion
only in the boundary layer, the radial extent of the flame front during the initial transient phase was surprisingly large.
In the ram accelerator configuration the flame propagated upstream along both the projectile and tube wall boundary layers,
resulting in unstart.
Received 25 September 1996 / Accepted 15 January 1997 相似文献
5.
Troy N. Eichmann Timothy J. McIntyre Alexis I. Bishop Sosefo Vakata Halina Rubinsztein-Dunlop 《Shock Waves》2007,16(4-5):299-307
Flow visualization experiments were performed for supersonic and hypersonic nitrogen test gas flows over a cylinder. The results
were used to quantify the influence of three-dimensional effects on optical line-of-sight visualization measurements. Images
of cylindrical models of varying aspect ratios (length to diameter) were taken. Shock stand-off distance measurements for
the models were compared with a two-dimensional approximation and numerical simulations. For aspect ratios of two and above,
the two-dimensional approximation was acceptable within experimental uncertainty. The measured shock stand-off decreased by
less than 5% from an asymptotic value for an infinite length cylinder. For smaller aspect ratios, a correction factor for
the shock stand-off needs to be applied if comparisons between the two-dimensional approximation and experimental measurements
are to be drawn. An estimate of this correction factor has been derived from an empirical fit to the available data.
相似文献
6.
Rajiv R. Thareja James R. Stewart Obey Hassan Ken Morgan Jaime Peraire 《国际流体数值方法杂志》1989,9(4):405-425
An upwind finite element technique that uses cell-centred quantities and implicit and/or explicit time marching has been developed for computing hypersonic laminar viscous flows using adaptive triangular grids. The approach is an extension to unstructured grids of the LAURA algorithm due to Gnoffo. A structured grid of quadrilaterals is laid out near a solid surface. For inviscid flows the method is stable at Courant numbers of over 100000. A first-order basic scheme and a higher-order flux-corrected transport (FCT) scheme have been implemented. This technique has been applied to the problem of predicting type III and IV shock wave interactions on a cylinder, with a view to simulating the pressure and heating rate augmentation caused by an impinging shock on the leading edge of a cowl lip of an engine inlet. The predictions of wall pressure and heating rates compare very well with experimental data. The flow features are distinctly captured with a sequence of adaptively generated grids. 相似文献
7.
A theoretical model of an elastic panel in hypersonic flow is derived to be used for design and analysis. The nonlinear von Kármán plate equations are coupled with 1st order Piston Theory and linearized at the nonlinear steady-state deformation due to static pressure differential and thermal loads. Eigenvalue analysis is applied to determine the system’s stability, natural frequencies and mode shapes. Numerically time marching the equations provides transient response prediction which can be used to estimate limit cycle oscillation amplitude, frequency and time to onset. The model’s predictive capability is assessed by comparison to an experiment conducted at a free stream flow of Mach 6. Good agreement is shown between the theoretical and experimental natural frequencies and mode shapes of the fluid–structure system. Stability analysis is performed using linear and nonlinear methods to plot stability, flutter and buckling zones on a free stream static pressure vs temperature differential plane. 相似文献
8.
Numerical and experimental techniques are used to model the flow and pressure distribution around the forebody of the HYFLEX
hypersonic flight vehicle. We compare numerical simulation results with modified Newtonian theory and flight data to determine
the accuracy of the computational fluid dynamics (CFD) technique used. The numerical simulations closely match the trends
in flight data, and show that real gas effects have a small but significant influence on the nose pressure distribution. We
also present pressure results from a scale-model tested in a shock tunnel, and compare them with simulation results. For the
shock tunnel experiment, the model was placed such that part of the upper surface was in a region of the test flow where nonuniformities
were significant, and it was shown that the numerical simulation could adequately capture these experimental flow features.
The binary scaling parameter (describing the similarity in species dissociation between flight and model) was used to design
the scale-model tests in the shock tunnel, and its effectiveness is discussed. We find that matching the flight Mach number
in the shock tunnel experiment is not critical for reproducing flight pressure data, so long as flight velocity is matched,
and binary scaling is maintained.
Received 11 June 1998 / Accepted 1 September 1998 相似文献
9.
We present the extension of our wall-laws developed for low-speed flows to super-and hyper-sonic configurations. In particular, we are interested in flows over isothermal walls and in the modeling of heat transfer. We recall the main steps of the development: ?Obtaining generalized wall functions for low-speed fluids, valid for all y +. ?Taking into account transversal effects in wall-laws. ?Accounting for the compressible feature of the flow on adiabatic walls without using information on the local boundary layer structure, for instance its thickness, but only using information available at the fictitious wall. ?Taking into account thermal effects on isothermal walls. In particular, the heat flux at the real wall is obtained by an a posteriori evaluation using information at the fictitious one. ?Only using information available on unstructured meshes and avoiding the information coming from a Cartesian hypothesis for the mesh in near-wall regions. These ingredients are validated on hyper-sonic configurations on adiabatic and isothermal walls for expansion and compression ramps. 相似文献
10.