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1.
Abstract. The starting process of two-dimensional and axisymmetric nozzle flows has been investigated numerically. Special attention
has been paid to the early phase of the starting process and to the appearance of a strong secondary shock wave. For both
cases, shock intensities and velocities are obtained and discussed. The flow evolution in the axisymmetric case is proved
to be more complex and the transient starting process is slower than in the plane case. Finally, the effects of changing the
nozzle angle and the incident shock wave Mach number on the transient flow are addressed. It is shown that a faster start-up
can be induced either by decreasing the nozzle angle or increasing the Mach number of the incident shock wave.
Received 16 November 2001 / Accepted 24 September 2002 / Published online 4 December 2002
Correspondence to:A.-S. Mouronval (e-mail: mouronv@coria.fr) 相似文献
2.
The starting process of the flow in a wedge-like expansion nozzle of a shock tunnel is simulated by an unsplit 2-D GRP scheme
on an unstructured grid. The scheme is briefly outlined and results are presented and discussed in comparison to the experimental
(shadowgraph) findings obtained by Amann. The simulated pattern of reflected and transmitted shock waves in the nozzle inlet
region and inside the nozzle is found to agree well with the experimental data.
Received 5 April 1996 / Accepted 16 June 1997 相似文献
3.
We propose to find out numerical solutions of a travelling shock wave in condensed mixtures by using a direct numerical simulation.
Condensed multiphase materials under shock wave conditions are mechanically characterized by a unique pressure and a unique
velocity. In this study, the mixture is considered as a collection of grains separated by interface between each material:
this problem of interfaces is solved by a diffuse interface method. The results will be compared to existing one-dimensional
numerical models, analytical solutions and also experimental data. The volume fraction (or the phase temperature) is not measured
in experiments and it is then important to verify the behaviour of a phase quantity through various methods. A non-monotonous
evolution of the volume fraction is obtained with analytical solution as well as numerical simulation.
相似文献
4.
The problem of attenuating the noise from weapons firing is studied experimentally and numerically. As a possible method of attenuating the noise significantly, a silencer with no internal baffles is attached to the M242 cannon. The internal pressures inside the muffler are measured. The near-field overpressures outside the muffler at various polar angles are also measured. A numerical simulation of the flow through the muffler is performed, using Harten's shock-capturing method to solve the Euler equations of ideal compressible flow. The numerical simulation yields a detailed picture of the flow field as displayed by the pressure and Mach contours. Pressure–time curves at selected locations are obtained and compared with experimental data. There is good agreement, except that the numerical simulation generates more vigorous oscillations. 相似文献
5.
Different vibration-dissociation-vibration coupling models have been used to compute the nonequilibrium N-CH-Ar mixture flow behind a normal shock wave. A three-temperature model was used and the diffuse nature of vibrational relaxation
at high temperatures was accounted for. The numerical results obtained with the Treanor and Marrone model (preferential or
non preferential) and the Park model of vibration-dissociation-vibration coupling are compared. These results show that the
temperatures and the concentrations are mainly affected by the value of the characteristic temperature U in the preferential
model of Marrone and Treanor. An assessment of the more realistic model was realized by comparing numerical results with shock
tube experiments. The influence of argon addition on the nonequilibrium emission of CN behind the shock wave was also numerically
studied and compared to experimental measurements.
Received 1 September 1995 / Accepted 10 December 1996 相似文献
6.
P. Kosinski 《Shock Waves》2006,15(1):13-20
The problem of wave propagation in a dust–air mixture inside a branched channel has not been studied widely in literature, even though this topic has many important applications especially in process safety (dust explosions). In this paper, a shock wave interaction with a cloud of solid particles, and the further behaviour of both gas and particulate phases were studied using numerical techniques. The geometry mimicked a real channel where bends or branches are common. Two numerical approaches were used: Eulerian–Eulerian and Eulerian–Lagrangian. Using Eulerian-Lagrangian simulation, it was possible to include the effects of particle–particle and particle–wall collisions in a realistic and direct manner. Results are mainly shown as snap-shots of particle positions during the simulations and statistics for the particle displacement. The results show that collisions significantly influence the process of particle cloud formation.
PACS47.40.Nm, 02.60.Cb, 47.55.kf 相似文献
7.
A great number of experimental data indicating shock wave/boundary layer interactions in internal or external supersonic flows
were reviewed to make clear the mechanism of the interaction and to decide the onset of shock-induced separation. The interesting
conclusions were obtained for the considerably wide range of flow geometries that the onset of separation is independent of
the flow geometries and the boundary layer Reynolds number. It is found that the pressure rise necessary to separate the boundary
layer in supersonic external flows could be applied to such internal flows as overexpanded nozzles or diffusers. This is due
to the fact that the separation phenomenon caused by shock wave/boundary layer interactions is processed through a supersonic
deceleration. The shock-induced separation in almost all of interacting flow fields is governed by the concept of free interaction,
and the onset of shock-induced separation is only a function of the Mach number just upstream of shock wave. However, physical
scales of the produced separation are not independent of the downstream flow fields. 相似文献
8.
V.V. Shuvalov 《Shock Waves》1999,9(6):381-390
Eulerian, three-dimensional, numerical code, which conserves mass, momentum and energy simultaneously both in the Lagrangian
and remap steps, is developed. The use of special form of linear viscosity provides a weaker time step restriction as compared
with the Courant condition. The code is designed to investigate the multi-material problems, including dusty flows. The performance
of the code is illustrated by the modeling of shock wave interaction with a dusty thermal layer.
Received 15 June 1998/ Accepted 6 January 1999 相似文献
9.
In this paper, the wave pattern characteristics of shock-induced two-phase nozzle flows with the quiescent or moving dusty
gas ahead of the incident-shock front has been investigated by using high-resolution numerical method. As compared with the
corresponding results in single-phase nozzle flows of the pure gas, obvious differences between these two kinds of flows can
be obtained.
Received 14 June 1996 / Accepted 19 October 1996 相似文献
10.
Planar laser-induced fluorescence visualisation is used to investigate nonuniformities in the flow of a hypersonic conical nozzle. Possible causes for the nonuniformity are outlined and investigated, and the problem is shown to be due to a small step at the nozzle throat. Entrainment of cold boundary layer gas is postulated as the cause of the signal nonuniformity.
PACS 47.80.Jk, 47.40.Ki, 47.60.+i 相似文献
11.
Investigation of the starting process in a Ludwieg tube 总被引:1,自引:0,他引:1
The hypersonic Ludwieg tube Braunschweig (HLB) is a valve-controlled wind tunnel that has been designed for a Mach number
of Ma = 5.9 and a Reynolds number range from 2.5 × 106 up to 2.5 × 107 1/m. The intermittent working principle implies an unsteady onset of flow, which leads to a delay of the time frame suitable
for measurements as well as to heat loads different from steady flow conditions. This work numerically simulates the starting
process. It determines whether the onset of flow leads to a significant temperature rise in the model surface which in turn
impacts results gathered during measurement time. The flow field in the HLB is numerically rebuilt for two operating points
including valve opening. The non-stationary flow around a hyperboloid/flare configuration in the test section is calculated
for one operating point including surface heating. For laminar flow it is found that due to the short duration of the starting
process no significant model heating affects results obtained during measurement time.
相似文献
12.
A simple entrainment model is used to estimate droplet streamlines, velocity and mass flux in rocket exhaust plumes. Since
droplet mass flux constitutes only about 1% of the exhaust mass flux, the effect of droplet entrainment on the gas flow is
neglected. The novelty of the present model is in obtaining the droplet distribution within the nozzle by assuming a small
radial random velocity component for droplets at the throat. Gas flow in the nozzle is approximated as isentropic plus a correction
for the boundary layer. The computed distribution of droplet mass flux is found to be in good agreement with experimental
data.
Received 15 January 1996 / Accepted 11 September 1996 相似文献
13.
14.
In this paper we wish to demonstrate to what extent the numerical method regularized smoothed particle hydrodynamics (RSPH) is capable of modelling shocks and shock reflection patterns in a satisfactory manner. The use of SPH based methods to model shock wave problems has been relatively sparse, both due to historical reasons, as the method was originally developed for studies of astrophysical gas dynamics, but also due to the fact that boundary treatment in Lagrangian methods may be a difficult task. The boundary conditions have therefore been given special attention in this paper. Results presented for one quasi-stationary and three non-stationary flow tests reveal a high degree of similarity, when compared to published numerical and experimental data. The difference is found to be below 5, in the case where experimental data was found tabulated. The transition from regular reflection (RR) to Mach reflection (MR) and the opposite transition from MR to RR are studied. The results are found to be in close agreement with the results obtained from various empirical and semi-empirical formulas published in the literature. A convergence test shows a convergence rate slightly steeper than linear, comparable to what is found for other numerical methods when shocks are involved. 相似文献
15.
Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the prac-ticability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disinte-grates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17%occurs with a triangular shape, while the max-imum increase in aerodynamic efficiency (lift-to-drag ratio) of around 10%happens with a rectangular shape at an angle of attack of 2.26?. 相似文献
16.
The importance of the lift force acting on the dispersed phase in the boundary layer of a laminar gas-particle dilute mixture
flow generated by a shock wave is investigated numerically. The particle phase is supposed to form a continuum and is described
by an Eulerian approach. The ability of the Eulerian model to simulate particle flows and the importance of the two-way coupling
are proven by comparison with experimental data as well as with the numerical results from schemes based on a Lagrangian approach.
The models used for the lift force are discussed through comparisons between numerical and experimental results found in the
literature. Some results about the formation of a dust cloud are numerically reproduced and show the major role of the lift
force. Simulations of two-dimensional two-phase shock tube flows are also performed including the lift force effects. Although
the wave propagation is weakly influenced by the lift force, the force modifies substantially the dynamics of the flow near
the wall.
Received 17 February 2000 / Accepted 30 November 2000 相似文献
17.
Abderrahmane Nebbache 《Comptes Rendus Mecanique》2018,346(9):844-854
A separated turbulent flow in an axisymmetrical nozzle is studied numerically. Two configurations nozzle are investigated. The first one is the truncated ideal contour nozzle, DLR-TIC, is fed with nitrogen. The second configuration is called the thrust optimized contour nozzle or TOC type, ONERA-TOC, where the operating gas is a hot air. The classical pattern of a free shock separation is obtained for different values of the nozzle pressure ratio. The results are compared and validated using experimental data. 相似文献
18.
Zeguang Pei Chongwen Yu 《Journal of Fluids and Structures》2011,27(1):121-133
Murata vortex spinning (MVS) is a recently developed spinning technology which utilizes high speed swirling airflow to insert twist into the yarn. The motional characteristics of the flexible fibers in the airflow inside the MVS nozzle are of vital importance to the yarn formation mechanism and properties. The fiber motion in the MVS nozzle involves fluid-structure interaction (FSI) and contact problems. In this paper, a two-dimensional FSI model combined with the fiber-wall contact is introduced to simulate a single fiber moving in the airflow inside the MVS nozzle. The model is solved using a finite element code ADINA. Based on the model, the motional characteristics of the fiber are analyzed and the effect of two process parameters - the nozzle pressure and yarn delivery speed - on the fiber motion and, in turn, the yarn tenacity is discussed. The results indicate that the fiber firstly undergoes a false-twisting process. Subsequently, its trailing end splays out and whirls within the nozzle chamber for several turns to helically wrap and make the spun yarn. The results also show that the effect of the nozzle pressure on the tenacity of the produced MVS yarn is not obvious. The increased yarn delivery speed leads to the decreased MVS yarn tenacity. The numerical results show good agreement with the experimental results provided by other researchers. 相似文献
19.
A holographic interferometric study was made of the focusing of reflected shock waves from a circular reflector. A diaphragmless
shock tube was used for incident shock Mach numbers ranging from 1.03 to 1.74. Hence, the process of reflected shock wave
focusing was quantitatively observed. It is found that a converging shock wave along the curved wall undergoes an unsteady
evolution of mach reflection and its focusing is, therefore, subject to the evolution of the process of shock wave reflections.
The collision of triple points terminates the focusing process at the geometrical focus. In order to interprete quantitatively
these interferograms, a numerical simulation using an Eulerian solver combined with adaptive unstructured grids was carried
out. It is found numerically that the highest density appears immediately after the triple point collision. This implies that
the final stage of focusing is mainly determined by the interaction between shock waves and vortices. The interaction of finite
strength shock waves, hence, prevents a curved shock wave from creating the infinite increase of density or pressure at a
focal point which is otherwise predicted by the linear acoustic theory. 相似文献
20.
M. B. Tyndall 《Shock Waves》1993,3(1):55-66
Results are presented for a range of one- and two-dimensional shock-wave problems in elastic-plastic and hydrodynamic metals. These problems were solved numerically using the Flux-Corrected Transport (FCT) technique which achieves high resolution without non-physical oscillations, especially at shock fronts, and has not been used before in elastic-plastic solids. The two-dimensional problems were solved using both operator- and non-operator-split techniques to highlight the significant differences between these techniques when solving shock-wave problems in elastic-plastic solids. Comparisons of the elastic-plastic solutions with the hydrodynamic solutions are made and illustrate the importance of including elastic-plastic conditions when modelling the behaviour of solids. Also, the errors in these solutions that are due to the initial conditions are discussed in detail.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献