共查询到20条相似文献,搜索用时 15 毫秒
1.
J. F. Milthorpe 《国际流体数值方法杂志》1992,14(3):267-288
A simple convection algorithm for simulation of time-dependent supersonic and hypersonic flows of a perfect but viscous gas is described. The algorithm is based on conservation and convection of mass, momentum and energy in a grid of rectangular cells. Examples are given for starting flow in a shock tube and oblique shocks generated by a wedge at Mach numbers up to 30·4. Good comparisons are achieved with well-known perfect gas flows. 相似文献
2.
The application of grid stretching or grid adaptation is generally required in order to optimize the distribution of nodal points for fluid-dynamic simulation. This is necessitated by the presence of disjoint high gradient zones, that represent boundary or free shear layers, reversed flow or vortical flow regions, triple deck structures, etc. A domain decomposition method can be used in conjunction with an adaptive multigrid algorithm to provide an effective methodology for the development of optimal grids. In the present study, the Navier-Stokes (NS) equations are approximated with a reduced Navier-Stokes (RNS) system, that represents the lowest-order terms in an asymptotic Re expansion. This system allows for simplified boundary conditions, more generality in the location of the outflow boundary, and ensures mass conservation in all subdomain grid interfaces, as well as at the outflow boundary. The higher-order (NS) diffusion terms are included through a deferred corrector, in selected subdomains, when necessary. Adaptivity in the direction of refinement is achieved by grid splitting or domain decomposition in each level of the multigrid procedure. Normalized truncation error estimates of key derivatives are used to determine the boundaries of these subdomains. The refinement is optimized in two co-ordinate directions independently. Multidirectional adaptivity eliminates the need for grid stretching so that uniform grids are specified in each subdomain. The overall grid consists of multiple domains with different meshes and is, therefore, heavily graded. Results and computational efficiency are discussed for the laminar flow over a finite length plate and for the laminar internal flow in a backward-facing step channel. 相似文献
3.
Generalized reference enthalpy formulations and simulation of viscous effects in hypersonic flow 总被引:1,自引:0,他引:1
G. Simeonides 《Shock Waves》1998,8(3):161-172
A generalized reference enthalpy formulation for the skin friction, heat transfer and radiation-equilibrium temperature distributions
over aerodynamic surfaces in attached hypersonic / hyperenthalpic flow is proposed. The formulation, which has been extensively
employed in various forms by numerous investigators in the perfect gas regime, has also been recently demonstrated to provide
adequate estimates of the heat transfer distribution in thermochemically active high enthalpy flow conditions when coupled
to thermochemically active Euler solutions. It is now used to reveal the relevant similitude parameters for viscous effects
in hypersonic flow, and the importance of the temperature distribution across the boundary layer and of the temperature-viscosity
relation. It is shown that, although reproduction of the flight total flow enthalpy as well as surface temperature is the
obvious solution for full viscous simulation in (perfect gas) hypersonic flow, the hot surface testing requirement and, in
a number of practical applications, also the hot flow requirement may be relaxed with reasonably small error that can be of
the same order as the measurement accuracy in present-day hypersonic testing. This similitude error, however, may increase
significantly in cases exhibiting strong viscous/inviscid interaction or when the laminar-turbulent transition process becomes
important. In this respect, alternative full simulation solutions, which are less demanding in terms of reproduction of the
high levels of flight freestream and surface temperature or even Reynolds number, are discussed.
Received 6 May 1997 / Accepted 8 October 1997 相似文献
4.
The paper discusses flat plate boundary layer transition in supersonic/hypersonic flow conditions. Examination of experimental infrared thermography data illustrates the importance of the leading edge thickness and (non-) uniformity to the transition process. Such observations have triggered the collection of a wide range of experimental data on supersonic/hypersonic flat plate boundary layer transition, and a number of attempts to correlate this data with characteristic parameters including leading edge thickness. Results indicate a strong dependence of the relevant transition parameters on the pressure field in the transition region, as this is determined by the combined effects of leading edge thickness and boundary layer growth/viscous interaction, and particularly on the relative importance of the two effects. In fact, two distinct correlation zones are established, depending on whether the pressure distribution at the onset of transition is dominated by leading edge bluntness effects or by boundary layer growth and viscous interaction, thus limiting the observed data scatter to reasonable levels.Received: 13 August 2002, Accepted: 7 February 2003, Published online: 28 April 2003 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.
R. Hillier R.R. Boyce S.A. Creighton A. Fiala A.P. Jackson S.G. Mallinson A.H. Sheikh S. Soltani S. Williams 《Shock Waves》2003,12(5):375-384
Abstract. This paper presents a set of test cases in high speed aerodynamics that describe our perceived relationship between experiment
and computation. Computational fluid dynamics, with sensible interpretation, can guide experimental design, so that wind tunnel
studies can focus better on fundamental ‘benchmark’ studies. Likewise experimental data may be used as feed back to evaluate
codes and to improve their physical modelling. Here we present several test cases, developed in our laboratory, that we regard
as basic ‘building blocks’ for high speed aerodynamics. These include: design for boundary-layer/pressure-gradient interaction;
cavity flows; shock-wave/boundary-layer interactions; techniques for a graduated and controlled study of three-dimensional
separated flows.
Received 10 October 2001/ Accepted 19 November 2002 Published online 4 February 2003
Correspondence to: R. Hillier (r.hillier@ic.ac.uk)
An abridged version of this paper was presented at the 23rd Int. Symposium on Shock Waves at Fort Worth, Texas, from July
22 to 27, 2001 相似文献
7.
《Particuology》2014
In this study the flow field and the nanoparticle collection efficiency of supersonic/hypersonic impactors with different nozzle shapes were studied using a computational modeling approach. The aim of this study was to develop a nozzle design for supersonic/hypersonic impactors with the smallest possible cut-off size d50 and rather sharp collection efficiency curves. The simulation results show that the changes in the angle and width of a converging nozzle do not alter the cut-off size of the impactor; however, using a conical Laval nozzle with an L/Dn ratio less than or equal to 2 reduced d50. The effect of using a cap as a focuser in the nozzle of a supersonic/hypersonic impactor was also investigated. The results show that adding a cap in front of the nozzle had a noticeable effect on decreasing the cut-off size of the impactor. Both flat disks and conical caps were examined, and it was observed that the nozzle with the conical cap had a lower cut-off size. 相似文献
8.
Oscillatory flows of a choked underexpanded supersonic impinging jet issuing from a convergent nozzle have been computed using
the axisymmetric unsteady Navier--Stokes system. This paper focuses on the oscillatory flow features associated with the variation
of the nozzle-to-plate distance and nozzle pressure ratio. Frequencies of the surface pressure oscillation and flow structural
changes from computational results have been analyzed. Staging behavior of the oscillation frequency has been observed for
both cases of nozzle-to-plate distance variation and pressure ratio variation. However, the staging behavior for each case
exhibits different features. These two distinct staging behaviors of the oscillation frequency are found to correlate well
if the frequency and the distance are normalized by the length of the shock cell. It is further found that the staging behavior
is strongly correlated with the change of the pressure wave pattern in the jet shear layer, but not with the shock cell structure.
Communicated by K. Takayama
PACS 02.60.Cb; 47.40.−x; 47.40.Nm; 47.35.+I; 47.15.−x 相似文献
9.
Numerical study of the oscillations induced by shock/shock interaction in hypersonic double-wedge flows 总被引:1,自引:0,他引:1
In this paper, the shock pattern oscillations induced by shock/shock interactions over double-wedge geometries in hypersonic
flows were studied numerically by solving 2D inviscid Euler equations for a multi-species system. Laminar viscous effects
were considered in some cases. Temperature-dependent thermodynamic properties were employed in the state and energy equations
for consideration of the distinct change of the thermodynamic state. It was shown that the oscillation results in high-frequency
fluctuations of heating and pressure loads over wedge surfaces. In a case with a relatively lower free-stream Mach number,
the shock/shock interaction structure maintains a seven-shock configuration during the entire oscillation process. On the
other hand, the oscillation is accompanied by a transition between a six-shock configuration (regular interaction) and a seven-shock
configuration (Mach interaction) in a case with a higher free-stream Mach number. Numerical results also indicate that the
critical wedge angle for the transition from a steady to an oscillation solution is higher compared to the corresponding value
in earlier numerical research in which the perfect diatomic gas model was used.
相似文献
10.
A Lagrangian framework is set out to describe turbulent non-premixed combustion in high speed coflowing jet flows. The final aim is to provide a robust computational methodology to simulate, in various conditions, the underexpanded GH2/GO2 torch jet that is used to initiate combustion in an expander cycle engine. The proposed approach relies on an early modelling proposal of Borghi and his coworkers. The model is well suited to describe finite rate chemistry effects and its recent extension to high speed flows allows one to take the influence of viscous dissipation phenomena into account. Indeed, since the chemical source terms are highly temperature sensitive, the influence of viscous phenomena on the thermal runaway is likely to be all the more pronounced since the Mach number values are high. The validation of the extended model has been recently performed through the numerical simulation of two distinct well-documented experimental databases. Only a brief summary of this preliminary validation step is provided here. The main purpose of the present work is to proceed with the numerical simulation of geometries that bring together the essential peculiarities of the underexpanded GH2/GO2 torch. The behavior of the corresponding supersonic coflowing jet flames for various conditions is discussed in the light of computational results. To cite this article: J.-F. Izard, A. Mura, C. R. Mecanique 337 (2009). 相似文献
11.
Chang Qianshun 《国际流体数值方法杂志》1987,7(7):719-731
The splitting difference scheme is used to study flow separation. Flows behind a circular cylinder are computed as a model problem. In view of the nature of the flow, the variables are transformed. The boundary condition for the pressure is given from an intermediate velocity. The free-slip velocity boundary conditions on the rigid wall are given by interpolation. The multigrid algorithm is applied to the pressure iteration. We also choose better initial values for the model problem by means of the multigrid algorithm idea. 相似文献
12.
This study employs the Space-Time Conservation Element and Solution Element (CE/SE) method to determine the influence of downstream
flow conditions on Mach stem height. The results indicate that the Mach stem height depends on the incident shock wave angle
and the distance between the trailing edge and the symmetry plane. Furthermore, it is shown that the downstream length ratio
and the trailing edge angle do not affect the Mach stem height nor the Mach reflection (MR) configuration, and the Space-Time
Conservation Element and Solution Element method is able to simulate the MR as well as many other numerical schemes.
Communicated by K. Takayama
PACS 47.40.Nm 相似文献
13.
A numerical simulation of flow interactions due to a transverse sonic jet ejected from a two-dimensional slot into a hypersonic
stream is carried out to examine the capability of Navier–Stokes solutions in predicting a massively separated flow upstream
of the jet exit. Grid sensitivity has been studied using gradually refined meshes to address the numerical accuracy of the
discretised solution of the governing equations. Comparison has been made with published experimental data regarding the separation
and reattachment points and the pressure distribution in the separated region. Flow field visualisation provides further insight
into the interaction region and reveals a small clockwise vortex immediately ahead of the jet exit, which is found to be responsible
for the second peak in the surface pressure distribution.
Received 30 June 1998 / Accepted 27 September 1998 相似文献
14.
The unsteady aspects of shock-induced-separation patterns have been investigated inside a Mach 2 planar nozzle. The mean location
of the shock can vary by changing, relatively to the nozzle throat, the height of the second throat which is positioned downstream
of the square test section. This study focuses on the wall pressure fluctuations spectra and the unsteady behaviour of the
shock. Symmetric shock configurations appear both for the largest openings of the second throat, and for the smallest openings.
For an intermediate opening the shock system exhibits asymmetrical configurations. A coating with roughnesses sticked on the
throat part of the nozzle in order to modify the state of the incoming boundary layers (from smooth to rought turbulent statement)
is a driver for the asymmetry. The fluctuating displacements of the shock patterns were analysed by using an ultra fast shadowgraph
visualization technique. A spectral analysis of the unsteady wall pressure measurements has revealed low frequency phenomena
governed by large structure dynamics in the separated flows.
Communicated by K. Takayama
PACS 02.60.Cb; 05.10.Ln; 47.11.+j; 47.15.Cb; 47.40.Nm 相似文献
15.
16.
A new preferential vibration-dissociation-exchange reactions coupling model – labelled CVDEV – resulting from an extension
of the well-known Treanor and Marrone CVDV model, has been derived to take into account the coupling between the vibrational
excitation of the and molecules and the two Zeldovich exchange reactions. Analytical expressions for the exchange reactions coupling factor and
for the average vibrational energy lost – or gained – by a molecule through an exchange reaction have been developed. The
influence of such a coupling has been shown by means of numerical simulations of hypersonic air flows through normal and bow
shock waves. Code-to-code comparisons between our model and other recent approaches have been conducted. The infrared radiation
of nitric oxide behind a normal shock wave resulting from computations with the CVDEV model has been compared with other coupling
model results and to recent shock tube experimental data. These comparisons have shown a good agreement of our model results
with the experimental data. In this context, the results show the prominent influence of vibration coupling on the first Zeldovich reaction, and the absence of vibration coupling effects on the second Zeldovich reaction.
Received 30 June 1997 / Accepted 3 December 1997 相似文献
17.
Summary A numerical scheme is presented which employs the characteristic surfaces in space-time for solving Navier-Stokes equations
for compressible fluid flow. We consider the general case of a three-dimensional flow, a simplification of which yields the
equations of the two-dimensional case. Emphasis is put on the method itself. We apply it to simulate a laminar hypersonic
flow around a circular cylinder of a five-components gas mixture of nitrogen and oxygen with thermally perfect constituents
and at chemical nonequilibrium. First, the partial differential equations are transformed into a standard form with directional
derivatives, enabling to attain the compatibility conditions, including the viscosity terms. These conditions are discretized
by approximating their integrals along the corresponding characteristic surfaces. The result is an explicit time-marching
numerical scheme. Using a grid fitted between the shock and the cylinder, and starting from roughly estimated initial conditions,
a steady solution is searched. A comparison is made with the solution obtained under the assumption of a perfect gas.
Received 6 April 1999; accepted for publication 13 May 1999 相似文献
18.
An unstructured non‐nested multigrid method is presented for efficient simulation of unsteady incompressible Navier–Stokes flows. The Navier–Stokes solver is based on the artificial compressibility approach and a higher‐order characteristics‐based finite‐volume scheme on unstructured grids. Unsteady flow is calculated with an implicit dual time stepping scheme. For efficient computation of unsteady viscous flows over complex geometries, an unstructured multigrid method is developed to speed up the convergence rate of the dual time stepping calculation. The multigrid method is used to simulate the steady and unsteady incompressible viscous flows over a circular cylinder for validation and performance evaluation purposes. It is found that the multigrid method with three levels of grids results in a 75% reduction in CPU time for the steady flow calculation and 55% reduction for the unsteady flow calculation, compared with its single grid counterparts. The results obtained are compared with numerical solutions obtained by other researchers as well as experimental measurements wherever available and good agreements are obtained. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
19.
The supersonic and hypersonic.laminar and turbulent vi-scous separated flows over two and three-dimensional com-pression corners are solved by the antidissipative explicit-implicit difference scheme presented in this paper.The re-sults obtained show that a high accuracy has been achieved bythis method and the time needed for computation is greatlyreduced. 相似文献
20.
Numerical and experimental analyses are performed on a supersonic air ejector to evaluate the effectiveness of commonly-used computational techniques when predicting ejector flow characteristics. Three series of experimental curves at different operating conditions are compared with 2D and 3D simulations using RANS, steady, wall-resolved models. Four different turbulence models are tested: k–ε, k–ε realizable, k–ω SST, and the stress–ω Reynolds Stress Model. An extensive analysis is performed to interpret the differences between numerical and experimental results. The results show that while differences between turbulence models are typically small with respect to the prediction of global parameters such as ejector inlet mass flow rates and Mass Entrainment Ratio (MER), the k–ω SST model generally performs best whereas ε-based models are more accurate at low motive pressures. Good agreement is found across all 2D and 3D models at on-design conditions. However, prediction at off-design conditions is only acceptable with 3D models, making 3D simulations mandatory to correctly predict the critical pressure and achieve reasonable results at off-design conditions. This may partly depend on the specific geometry under consideration, which in the present study has a rectangular cross section with low aspect ratio. 相似文献