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1.
The problem of the stabilization of the diffusion-induced flow over a sphere submerged in a continuously stratified fluid is solved using both asymptotic and numerical methods. The analytical solution describes the structure of the main convective cells, including thin meridional jets flowing along the surface and plumes spreading from the flow convergence regions above the upper and lower poles of the sphere which gradually return the fluid particles to the neutral buoyancy horizon. The total width of the flows adjacent to the surface exceeds the thickness of the salinity deficit layer or the density boundary layer. The numerical solution of the complete problem in the nonlinear formulation describes the main convective cells and two systems of unsteady integral waves formed in the vicinity of the sphere poles. At large times, out of the entire system of internal waves only those nearest to the neighborhood of their horizon of formation remain clearly defined. The calculated flow patterns are in agreement with each other and the data of shadow visualization of the stratified fluid structure near a submerged obstacle at rest. 相似文献
2.
Transformation of hanging discontinuities into vortex systems in a stratified flow behind a cylinder
The mechanisms of formation of hanging discontinuities, vortex dipoles, and vortex arrays in the wave wake behind a cylinder moving at a constant velocity in a stratified fluid are investigated using various schlieren methods. The existence of discontinuities is attributable to the distortion of the internal-wave phase pattern in the shear flow and to the varying stratification and subsequent interaction of the waves with the appearing nonuniformities. Hanging discontinuities and vortex systems are low-velocity analogs of shock waves. An analysis of the internal-wave pattern indicates that the values of the normal velocity component differ on the upper and lower edges of the discontinuities. A regime diagram for flows of this kind is given. 相似文献
3.
An analytical solution of a linearized problem of the emission of periodic internal waves by part of a plane which oscillates with a small amplitude in an arbitrary direction in a viscous exponentially stratified fluid is constructed. Solutions of the dispersion equation are given for all positions of the emitting surface (arbitrary, vertical, horizontal, and critical when one of the beam propagation directions is collinear with the emitting surface). The possibility of transition to the case of a uniform fluid, which is important for applications, is analyzed. 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.
R. N. Bardakov V. V. Mitkin Yu. D. Chashechkin 《Journal of Applied Mechanics and Technical Physics》2007,48(6):840-851
The pattern of disturbances arising during the motion of a strip along a horizontal surface in a continuously stratified fluid
with identified upstream and attached internal waves, boundary layers, and edge singularities is calculated in the liner approximation.
The flow pattern behind a flat plate moving with a constant velocity in a continuously stratified fluid is studied with the
use of the optical schlieren technique; transformation of waves and finely structured elements of the flow with increasing
plate velocity is analyzed. The calculated and experimentally observed patterns of internal waves at low velocities are demonstrated
to be in good agreement.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 6, pp. 77–91, November–December, 2007. 相似文献
6.
A. Yu. Kazakov 《Journal of Applied Mechanics and Technical Physics》2009,50(2):235-242
This paper studies the problem of pairs of horizontal shear flows of weakly stratified fluids with identical mass, momentum,
and energy fluxes. The initial problem is reduced to a system of two scalar equations for the main- and perturbed-flow parameters
by using bifurcation methods. The existence conditions for nontrivial branches of conjugate flows close to the main flow are
investigated.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 79–88, March–April, 2009. 相似文献
7.
I. V. Sturova 《Fluid Dynamics》2006,41(4):619-628
The plane problem of the small steady-state oscillations of a horizontal cylinder arbitrarily located in a three-layer fluid whose upper and lower layers are homogeneous and whose middle layer is linearly stratified is considered in the linear formulation using the Boussinesq approximation. The fluid is assumed to be ideal and incompressible. The method of mass sources distributed along the body contour is used in the internal wave generation regime and an integral equation for the fluid pressure is derived in the non-wave regime. The hydrodynamic load acting on the body is calculated as a function of the oscillation frequency of the cylinder and its location. The results are compared with experimental data. 相似文献
8.
Yu. D. Chashechkin 《Fluid Dynamics》1989,24(1):1-7
The flow pattern around a sphere moving at constant velocity in a fluid with an exponential density distribution is investigated by optical methods. The thin density boundary layer forming the high-gradient envelope of the wake is distinguished as one of the elements of the structure. The symmetry properties of the flow are investigated. The limits of applicability of the traditional approximation of weak stratification in the problem of excitation of attached internal waves are noted.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 3–9, January–February, 1989. 相似文献
9.
V. A. Gorodtsov 《Fluid Dynamics》2006,41(3):415-423
The problem of the wave drag of ellipsoids moving in a uniformly stratified ideal fluid is considered by means of modeling the bodies by surface distributions of mass sources. Analytical results are obtained using the distributions known from the theory of a uniform fluid, which make it possible to describe the emission of internal waves by rapidly moving ellipsoids of revolution (spheroids) in the limit of large Froude numbers. An asymptotically simplified form of the dependence of the wave drag on the Froude number and the spheroid axis ratio is found. In the particular case of a sphere, the result confirmed earlier by Greenslade by making comparisons with a numerical calculation and experimental data is obtained. 相似文献
10.
O. A. Druzhinin 《Fluid Dynamics》2009,44(2):213-223
The process of generation of internal waves by an initially cylindrical, turbulent jet with a Gaussian profile of the average horizontal velocity component in a fluid with stable linear density stratification is investigated by direct numerical simulation. It is shown that on time intervals Nt < 30, where N is the buoyancy frequency, the vertical velocity pulsations collapse, which is accompanied by the generation of internal waves whose spatial period is close to the wavelength of the spiral mode of jet instability in a homogeneous fluid. The wave dynamics and kinematics can be satisfactorily described by the linear theory for a pulsed source and their parameters are in good agreement with the parameters of the “coherent” internal waves generated by a stratified wake in a laboratory experiment. At large times the wave generation ceases and the variations of the fluid density are localized in the neighborhood of the centers of large-scale vortices formed in the horizontal plane in the neighborhood of the jet. 相似文献
11.
A three-dimensional ray theory is presented for calculating the phase configuration of internal waves around a moving disturbance
in a flow with arbitrary stratification and background shear. The theory is applied to two-dimensional stratified shear flows
which have been produced in the laboratory and good agreement is shown between the theoretical and experimental phase configurations.
Good agreement is also shown when caustics and critical levels are present. This paper includes the wave systems arising from
a combined translation and oscillatory motion of a source and it shows how distinct systems of waves arise from each, type
of motion under different background conditions. This paper shows that for two-dimensional steady wave systems the critical
level is at a well defined height which is independent of wavenumber but in three dimensions the critical height can in general
vary with wavenumber. 相似文献
12.
V. A. Gushchin V. V. Mitkin T. I. Rozhdestvenskaya Yu. D. Chashechkin 《Journal of Applied Mechanics and Technical Physics》2007,48(1):34-43
The fine structure of the flow field of a continuously stratified fluid around a circular cylinder for small values of the
Froude number was investigated in laboratory and numerical experiments. The parameters of the leading perturbation, the internal-wave
field, and the cylinder wake were calculated using a two-dimensional model. The existence of the previously experimentally
observed high-gradient density layers in the wake that are parallel to the flow axis was for the first time confirmed by numerical
calculations. Results of the numerical and experimental studies are in good agreement with each other and with analytical
models for small values of the Froude number.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 43–54, January–February, 2007. 相似文献
13.
J. B. Flor W. S. S. Govers G. J. F. Van Heijst R. Van Sluis 《Applied Scientific Research》1993,51(1-2):405-409
This paper reports on an experimental study of vortices in a stratified fluid. The vortices were generated by two different stirring devices, viz. a rotating sphere and a rotating bent rod. It was found that the vortices created with the rotating sphere are mostly axisymmetric and stable, whereas the vortices produced with the bent rod generally show instabilities, under certain conditions leading to the formation of a tripolar vortex. This report concentrates on this tripolar structure and presents quantitative information about the flow obtained through streak photography of tracer particles. 相似文献
14.
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 55–60, March–April, 1991. 相似文献
15.
Yunxiaing You Tianqun Hu Hao Xu Yongliu Fang Zhong Yu Zhongmin Shi Yan Qu Yue Xiao 《力学学报》2010,42(3):400
对密度分层流体中内波与半潜平台的相互作用问题
进行了模型试验研究. 采用摇板方法进行了内波造波试验,对内波波长、周期和波高进行了
测量分析,获得了内波波高和波长与周期之间的相关关系. 利用激光和倾角仪方法对半潜平
台的纵荡和纵摇运动响应进行了测量分析,获得了平台纵荡运动及纵摇角幅值与内波周期之
间的相关关系. 结果表明,在半潜平台的设计与应用中,内波对其运动响应的影响是不可忽
视的. 特别地,发现了在内波周期的某个范围内, 半潜平台的纵荡和纵摇都会出现
倍频周期运动响应的现象. 相似文献
16.
Internal waves from a body accelerating in a thermocline 总被引:1,自引:0,他引:1
Many papers study the steady wave system around bodies moving in thermoclines but little attention has been given to unsteady wave systems. This paper concentrates on the unsteady wave systems around accelerating bodies in thermoclines. The wave shapes are calculated using a theory derived from a dispersion relation based on an exp-tanh density profile. All modes of oscillation can be determined and it is shown that for the lowest mode both oblique and transverse waves occur whereas for the higher modes the presence of transverse waves depends on the background conditions and on the speed of the body. Cauchy-Poisson impulsive start waves are included. The theoretical wave shapes compare quite well with those calculated using finite-difference formulations of the full Navier-Stokes equations when a body accelerates from rest.It is also shown how the dispersion relation =N sin together with the WKB approximation can produce the same plan-view wave forms as those obtained using the thermocline wave dispersion relation given by [17, 30]. 相似文献
17.
18.
19.
Chia-Shun Yih 《Acta Mechanica Sinica》1993,9(3):193-209
A systematic procedure is proposed for obtaining solutions for solitary waves in stratified fluids. The stratification of
the fluid is assumed to be exponential or linear. Its comparison with existing results for an exponentially stratified fluid
shows agreement, and it is found that for the odd series of solutions the direction of displacement of the streamlines from
their asymptotic levels is reversed when the stratification is changed from exponential to linear. Finally the interaction
of solitary waves is considered, and the Korteweg-de Vries equation and the Boussinesq equation are derived. Thus the known
solutions of these equations can be relied upon to provide the answers to the interaction problem. 相似文献
20.
H. Houcine Yu. D. Chashechkin P. Fraunié H. J. S. Fernando A. Gharbi T. Lili 《国际流体数值方法杂志》2012,68(4):451-466
Numerical simulations of two‐dimensional stratified flow past an obstacle (thin vertical strip) were performed at relatively low Reynolds numbers. A finite differences solver was adopted to simultaneously solve Navier–Stokes equations together with transport equations for salinity (stratifying agent), and the standard Smagorinsky turbulent closure scheme was called in whenever necessary to account for turbulence. The emphases were on the evaluation of code for unsteady stratified flow applications as well as identification of transient and steady internal‐wave processes during flow past obstacles. Simulations were compared with laboratory experiments, where observations were made using a high resolution Schlieren technique and conductivity probes. Blocking was observed upstream of the obstacle, surrounded by near‐zero frequency internal waves, the phase lines of which joined those of lee waves through a transition zone in the proximity of the obstacle. This pattern was preceded by initial transients of the starting flow in which propagating internal waves played a dominant role. Confluence of isopycnals passing over/under the obstacle in the wake led to interesting flow phenomena, including the radiation of internal waves. The numerical simulations were in good agreement with observations, except that some phenomena could not be captured due to resolution issues of either numerical or experimental techniques. The efficacy of the code in point for stratified flow calculations with relevance to the atmosphere and oceans was confirmed. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献