共查询到20条相似文献,搜索用时 15 毫秒
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Interfacial wave parameters, in this case the frequency, height, velocity, and slope, were investigated experimentally in a horizontal air-water stratified flow. Experiments were conducted with a parallel wire conductance sensor and PIV visualization in a rectangular channel, of which the width and height are 40 mm and 50 mm, respectively. In the experiments, the flow condition covered the liquid Reynolds number Rel range of 450 to 3540 and the gas Reynolds number Reg range of 14,000 to 70,000. The results revealed that the observed wave types according to the flow conditions in the rectangular channel are similar to those in a horizontal pipe. The frequency, height, and slope of the interfacial wave show complicated tendencies according to the combination of Reg and Rel, which affects the coalescence and breakup of the wave. Specifically, the wave height and wave slope have opposite tendencies regarding the criterion of Reg = 34,000. For cases in which Reg ≥ 34,000, the interfacial drag force significantly affects the height and slope of the disturbance wave. In contrast, for Reg < 34,000, the growth of the wave has an important effect on the wave parameters. Finally, new empirical correlations for the frequency, height, and slope of the interfacial wave were proposed for application to the development of a droplet entrainment model in a horizontal stratified flow. 相似文献
3.
In this paper, the basic equation of internal long waves in stratified shear flow is derived under Boussinesq assumption,
the first order approximation solution is given for solitary waves with the effects of slowly varying topograph at the sea
bottom, weak stratification and basic shear flow.
The Project Supported by the National Natural Science Foundation of China. 相似文献
4.
The evolution of a few large scale high frequency standing internal waves confined to a vertical plane is studied numerically. The growth of nonlinear interactions leads to a transfer of energy toward small vertical scales and lower frequencies: the result is a steep energy decrease due to wave breaking. Induced mixing is evaluated. A parametric forcing is also introduced in order to compare with laboratory experiments. Wave breaking also occurs but as opposed to the unforced case different phases are next observed: internal wave growth due to constructive forcing alternate with energy decrease. 相似文献
5.
V.I. Shrira 《International Journal of Non》1981,16(2):129-138
The evolution of a three-dimensional packet of weakly non-linear internal gravity waves propagating obliquely at an arbitrary angle to the vertical line is considered. Two coupled non-linear equations connecting variations of a packet amplitude and induced flows are derived. three-dimensionality of the packet having been found responsible for the non-linearity of the system. Explicit formulae for the induced flow vertical component and the mean density field variation caused by packet propagation have been obtained. The plane wave is shown to be unstable at any arbitrary slope of the wave vector. The non-linear equation describing the evolution of the two-dimensional packet is derived in the subsequent order of the asymptotic scheme.It has been found possible for the packet to collapse. The collapse of internal waves packets may be one of the possible mechanisms of “blini”-shaped regions of mixed waters formation in the ocean. 相似文献
6.
Yu. V. Kistovich Yu. D. Chashechkin 《Journal of Applied Mechanics and Technical Physics》1998,39(5):729-737
Beams of harmonic internal waves in a liquid with smoothly changing stratification are calculated in the Boussinesq approximation
taking into account the effects of diffusion and viscosity. A procedure of local reduction of the beam in a medium with an
arbitrary smooth stratification to the case of an exponentially stratified liquid is constructed. The coefficient of energy
losses in the case of beam reflection on the critical level is calculated. Parameters of internal boundary flows with split
scales of velocity and density that are formed by a wave beam on discontinuities of the buoyancy frequency and its higher
derivatives are determined.
Institute of Problems of Mechanics, Russian Academy of Sciences, Moscow 117526. Translated from Prikladnaya Mekhanika i Tekhnicheskaya
Fizika, Vol. 39, No. 5, pp. 88–98, September–October, 1998. 相似文献
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Chantal Staquet 《Meccanica》1994,29(4):489-505
A numerical study is conducted to find out the conditions of occurrence of a secondary Kelvin-Helmholtz instability in the thin layers (referred to as baroclinic layers) that form in a stably-stratified shear layer. For this purpose, three high resolution calculations of a moderately stratified shear layer have been carried out, at a fixed Reynolds number. The wavelength of the initial perturbation is progressively increased, starting from the fundamental wavelength predicted by linear stability theory up to twice this fundamental wavelength. The baroclinic layer of the flow is shown to lengthen and destabilize progressively from one calculation to the other, eventually bearing a secondary Kelvin-Helmholtz instability. The structure and dynamics of the baroclinic layers of the three calculations are examined in the frame of a theoretical model proposed by Corcos and Sherman ([1]). An excellent agreement with the predictions of this model have been found. We next show that the stability of the layer is controlled by the large-scale Kelvin-Helmholtz vortex, via the strain field that it induces in the stagnation point region of the layer. A consequence of this study is that secondary Kelvin-Helmholtz instabilities are fostered by the pairing of primary Kelvin-Helmholtz vortices in a strongly-stratified shear layer.
Sommario E stato condotto uno studio numerico per trovare le condizioni in cui insorge una instabilità secondaria di Kelvin-Helmholtz negli strati sottili che si formano in uno strato di scorrimento stabilmente stratificato. A questo scopo sono state effettuate tre simulazioni ad alta risoluzione a fissato numero di Reynolds e stratificazione bassa. La lunghezza d'onda della perturbazione iniziale è stata progressivamente aumentata dalla lunghezza fondamentale predetta dalla teoria lineare della stabilità fino a due volte questa stessa lunghezza. È stato osservato che da una simulazione all'altra lo strato baroclino del flusso si allunga e si destabilizza progressivamente, generando eventualmente un'instabilità di Kelvin-Helmholtz secondaria. Utilizzando il modello teorico proposto da Corcos e Sherman (1976), per le tre simulazioni sono state analizzate la struttura e la dinamica dello strato baroclino. È stato trovato un accordo eccellente con le predizioni di questo modello. È stato in seguito mostrato che la stabilità dello strato è controllato dai vortici di Kelvin-Helmholtz di larga scala attraverso il campo di deformazione che inducono nella regione del punto di ristagno dello strato. Una conseguenza di questo studio è che le instabilità secondarie di Kelvin-Helmholtz sono forzate dall'accoppiamento dei vortici primari in uno strato di scorrimento fortemente stratificato.相似文献
9.
Two flow visualization techniques, the shadowgraph and the hydrogen bubbles, are combined to facilitate simultaneous observation of the vertical velocity profile and the density interfaces in a stratified mixing layer in an annulus. The experimental setup is described and some examples of the resulting photographs are presented and discussed. 相似文献
10.
A large stratified shear flow water channel facility 总被引:6,自引:0,他引:6
11.
John P. McHugh 《Theoretical and Computational Fluid Dynamics》2008,22(2):107-123
Internal waves propagating in an idealized two-layer atmosphere are studied numerically. The governing equations are the inviscid anelastic equations for a perfect gas atmosphere. The numerical formulation eliminates all variables in the linear terms except vertical velocity, which are then treated implicitly. Nonlinear terms are treated explicitly. The basic state is a two-layer flow with continuous density at the interface. Each layer has a unique constant for the Brunt–Väisälä frequency. Waves are forced at the bottom of the domain, are periodic in the horizontal direction, and form a finite wave packet in the vertical. The results show that the wave packet forms a mean flow that is confined to the interface region that persists long after the wave packet has moved away. Large-amplitude waves are forced to break beneath the interface. 相似文献
12.
V. A. Gorodtsov 《Fluid Dynamics》1988,23(2):237-244
Conclusions In the transitional stage of the evolution of small perturbations in a flowing stratified fluid various structures may be formed. The form of these structures will depend on the initial conditions, the velocity shear, the stratification, and the dissipative characteristics of the fluid. In some cases in the intermediate stage the perturbations may increase.However, at large times in the final dissipative stage all the perturbations decay and the structure of the longest-lived of them is fairly simple. Owing to the shear effect the surviving perturbations are highly elongated in the direction of flow. However, under the influence of the stratification, from all the perturbations with h L/g in the transverse plane perturbations of two types are gradually filtered out: internal waves and thin horizontal layered structures.In the presence of shear flow the layered structure in a stratified fluid is not only preserved but even becomes more sharply expressed owing to the suppression by the shear if many of the competing perturbations.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 94–102, March–April, 1988. 相似文献
13.
The results of theoretical analysis, which show that molecular heat or salt diffusion can stabilize the flow, are experimentally confirmed with reference to the problem of the motion of a density-stratified fluid towards an opening in a vertical wall. An asymptotic regime in which neither stratification nor diffusion affects the integral characteristics of the flow is established.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.1, pp. 35–40, January–February, 1993.The authors are grateful to O. F. Vasil'ev for his valuable contribution to the organization of the research. 相似文献
14.
B. K. Sen-Gupta 《Meccanica》1973,8(1):52-55
Summary In this paper, we consider a linear model for internal waves in a stratified fluid. The equations are generalised by Fourier analysis after the manner of Scorer(1949) who considered an infinite atmosphere.
相似文献
Sommario Si considera un modello lineare per le onde interne in un fluido stratificato. Le equazioni sono generalizzate con un'analisi di Fourier secondo il metodo di Scorer(1949) che ha considerato un'atmosfera infinita.
相似文献
15.
This paper describes the deformation of an elastic pipe submitted to gravity and to an internal fluid flow. The pipe is clamped horizontally at one end and free at the other end. As the fluid velocity increases, the shape changes from an elastic beam deflected by its own weight towards an horizontal position. The shape of the pipe is characterized experimentally and is compared with a theoretical model based on the Euler–Bernoulli approximation and the conservation of the fluid momentum. We study how the determination of the pipe deformation provides an estimation of the conveyed fluid flow. Finally, the vertical force produced by the conveyed fluid to lift off a mass is deduced. 相似文献
16.
Speckle velocimetry with forward scattering has been applied to measure and visualize the two-dimensional velocity field in an internal gravity wave. The wave was produced by towing a cylinder in vertical direction, normal to its axis, through stratified salt water. Neutrally buoyant tracer particles whose density was matched with the density distribution of the stratification were uniformly distributed in the test fluid. The experimental results verify the results of a linear theory in the far field of the wave.Most part of this work was performed when the three authors were with Institut für Thermo- und Fluiddynamik, Ruhr-Universität Bochum. 相似文献
17.
The linear stability of unstably stratified shear flows between two horizontal parallel plates has been investigated. The eigenvalue problem was solved numerically by making use of the expansion method in Chebyshev polynomials, and critical Rayleigh numbers were obtained accurately in the Reynolds number range of [0.01,100]. It was found that the critical Rayleigh number for two-dimensional disturbances increases with an increase of the Reynolds number. The result strongly supports previous stability analyses except for the analysis by Makino and Ishikawa (1985) in which a decrease of the critical Rayleigh number was obtained. For some cases, a discontinuity in the critical wavenumber occurs, due to the development of two extrema in the neutral stability boundary. 相似文献
18.
V. V. Mitkin Yu. D. Chashechkin 《Journal of Applied Mechanics and Technical Physics》1999,40(1):69-75
The flow pattern around a horizontal cylinder towed at constant velocity in a continuously stratified fluid is visualized
by the shadow method. The velocities in the leading flow disturbance, i. e., in the flow-blocking region ahead of the cylinder,
are presented. In the body wake, a new class of small-size structures in the density gradient field is revealed against the
background of a smooth velocity profile. The evolution of the flow pattern with variation of the parameters of body motion
is studied.
Institute of Mechanics Problems, Moscow 117526. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No.
1, pp. 80–88, January–February, 1999. 相似文献
19.
《European Journal of Mechanics - B/Fluids》2005,24(5):642-658
The ‘dam-break’ initial behaviour of an inviscid gravity current which is released from a lock and then propagates over a horizontal boundary at the base of a stratified ambient fluid is considered. Analytical and finite-difference solutions of the one-layer shallow-water equations are developed and compared for the linear stratification in a rectangular channel case, and corroborated by numerical solutions of the full two-dimensional Navier–Stokes equations. Extensions of the shallow-water solution to non-linear stratification, release from an elliptical reservoir, and axisymmetric geometry are also presented. The results indicate that the shallow-water formulation captures well the essential features of the motion, which are qualitatively similar to the non-stratified case, but with details modified by the stratification; in particular, the forward propagation of the head and the backward spread of the depression wave are reduced when the stratification increases. 相似文献