共查询到20条相似文献,搜索用时 15 毫秒
1.
We derive a fully nonlinear evolution equation that can describe the two-dimensional motion of finite-amplitude long internal waves in a uniformly stratified three-dimensional fluid of finite depth. The derived equation is the two-dimensional counterpart of the evolution equation obtained by Grimshaw and Yi [J. Fluid Mech. 229, 603 (1991)]. In the small-amplitude limit, our equation is reduced to the celebrated Kadomtsev-Petviashvili equation. 相似文献
2.
The Rayleigh-Bénard theory by Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000)] is extended towards very large Prandtl numbers Pr. The Nusselt number Nu is found here to be independent of Pr. However, for fixed Rayleigh numbers Ra a maximum in the Nu(Pr) dependence is predicted. We moreover offer the full functional dependences of Nu(Ra,Pr) and Re(Ra,Pr) within this extended theory, rather than only give the limiting power laws as done in J. Fluid. Mech. 407, 27 (2000). This enables us to more realistically describe the transitions between the various scaling regimes. 相似文献
3.
Herein, an efficient numerical method is presented to describe the flow of a liquid in an open channel with various types of bottom configurations. The method is developed for steady two-dimensional potential free surface flows. The resulting nonlinear problem is solved numerically by boundary integral equation methods. In addition weakly nonlinear solutions are derived. New solutions which complement those of Dias and Vanden-Broeck [J. Fluid Mech. 59, 93-102 (2004)] are presented. Furthermore some solutions for channel flows past dips in the bottom are discussed. 相似文献
4.
Using a multi-scaled, chaotic flow known as the KS model of turbulence [J.C.H. Fung, J.C.R. Hunt, A. Malik, R.J. Perkins, Kinematic simulation of homogeneous turbulence by unsteady random fourier modes, J. Fluid Mech. 236 (1992) 281-318], we investigate the dependence of Lyapunov exponents on various characteristics of the flow. We show that the KS model yields a power law relation between the Reynolds number and the maximum Lyapunov exponent, which is similar to that for a turbulent flow with the same energy spectrum. Our results show that the Lyapunov exponents are sensitive to the advection of small eddies by large eddies, which can be explained by considering the Lagrangian correlation time of the smallest scales. We also relate the number of stagnation points within a flow to the maximum Lyapunov exponent, and suggest a linear dependence between the two characteristics. 相似文献
5.
A. Salhi M. Omri 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):463-475
An analysis based on the available experimental data and second-order closures is made for a turbulent shear flow over a rotating
cylinder in a quiescent fluid. The near-wall behaviour of the non-linear model for the pressure-strain correlation proposed
by Speziale, Sarkar and Gatski [J. Fluid Mech. 245, 227 (1991)] is enlarged; and the methodology proposed by Lai and So [J. Fluid Mech. 221, 641 (1990)] is adopted to take into account the wall-effects. The radial profile of the curvature parameter, Rs, is examined in connection with the logarithmic law. It is shown that the log-layer is associated to the region where the
mean velocity profile, V, is related to the power of the radial distance as Computations reveal that this region corresponds to the state with the most destabilizing curvature effects; which can be
chararacterized by the minimum value of the parameter B
c
=2R
s
(1+2R
s
), and not that one of the parameter B=2R
s
(1+2R
s
)/(1+R
s
)2 firstly introduced by Bradshaw [J. Fluid Mech. 36, 171 (1969)] and extensively used to characterize the turbulence structure in curved flows.
Received 9 December 1997 相似文献
6.
N.K. Vitanov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):249-266
By means of the Howard-Busse method of the optimum theory of turbulence we obtain upper bounds on the convective heat transport
in a horizontal fluid layer heated from below and rotating about a vertical axis. We consider the interval of large Taylor
numbers where the intermediate layers of the optimum fields expand in the direction of the corresponding internal layers.
We consider the 1 - α-solution of the arising variational problem for the cases of rigid-stress-free, stress-free, and rigid
boundary conditions. For each kind of boundary condition we discuss four cases: two cases where the boundary layers are thinner
than the Ekman layers of the optimum field and two cases where the boundary layers are thicker than the Ekman layers. In most
cases we use an improved solution of the Euler-Lagrange equations of the variational problem for the intermediate layers of
the optimum fields. This solution leads to corrections of the thicknesses of the boundary layers of the optimum fields and
to lower upper bounds on the convective heat transport in comparison to the bounds obtained by Chan [J. Fluid Mech. 64, 477 (1974)] and Hunter and Riahi [J. Fluid Mech. 72, 433 (1975)]. Compared to the existing experimental data for the case of a fluid layer with rigid boundaries the corresponding
upper bounds on the convective heat transport is less than two times larger than the experimental results, the corresponding
upper bound on the convective heat transport, obtained by Hunter and Riahi is about 10% higher than the bound obtained in
this article. When Rayleigh number and Taylor number are high enough the upper bound on the convective heat transport ceases
to depend on the boundary conditions.
Received 30 January 2001 and Received in final form 28 May 2001 相似文献
7.
Large eddy simulation of a turbulent nonpremixed piloted methane jet flame (Sandia Flame D) 总被引:5,自引:0,他引:5
M.R.H. Sheikhi T.G. Drozda P. Givi F.A. Jaberi S.B. Pope 《Proceedings of the Combustion Institute》2005,30(1):549-556
Large eddy simulation (LES) is conducted of the Sandia Flame D [Proc. Combust. Inst. 27 (1998) 1087, Sandia National Laboratories (2004)], which is a turbulent piloted nonpremixed methane jet flame. The subgrid scale (SGS) closure is based on the scalar filtered mass density function (SFMDF) methodology [J. Fluid Mech. 401 (1999) 85]. The SFMDF is basically the mass weighted probability density function (PDF) of the SGS scalar quantities [Turbulent Flows (2000)]. For this flame (which exhibits little local extinction), a simple flamelet model is used to relate the instantaneous composition to the mixture fraction. The modelled SFMDF transport equation is solved by a hybrid finite-difference/Monte Carlo scheme. This is the first LES of a realistic turbulent flame using the transported PDF method as the SGS closure. The results via this method capture important features of the flame as observed experimentally. 相似文献
8.
9.
We determine the intrinsic longitudinal dispersivity l(d) of randomly packed monodisperse spheres by separating the intrinsic stochastic dispersivity l(d) from dispersion by unavoidable sample dependent flow heterogeneities. The measured l(d), scaled by the hydrodynamic radius r(h), coincide with theoretical predictions [Saffman, J. Fluid Mech. 7, 194 (1960)] for dispersion in an isotropic random network of identical capillaries of length l and radius a, for l/a=3.82, and with rescaled simulation results [Maier et al., Phys. Fluids 12, 2065 (2000)]. 相似文献
10.
The horizontal convection within a rectangular tank is numerically simulated. The flow is found to be unsteady at high Rayleigh numbers. There is a Hopf bifurcation of Ra from steady solutions to periodic solutions, and the critical Rayleigh number Rac is obtained to be Rac = 5.5377×10^8 for the middle plume forcing at Pr = 1, which is much larger than the value previously obtained. In addition, the unstable perturbations are always generated from the central jet, which implies that the onset of instability is due to velocity shear (shear instability) other than thermally dynamics (thermal instability). Finally, Paparella and Young's first hypotheses [J. Fluid Mech. 466 (2002) 205] about the destabilization of the flow is numerically proven, i.e. the middle plume forcing can lead to a destabilization of the flow. 相似文献
11.
B. Eckhardt S. Grossmann D. Lohse 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):541-544
We interpret measurements of the Reynolds number dependence of the torque in Taylor-Couette flow by Lewis and Swinney [Phys.
Rev. E 59, 5457 (1999)] and of the pressure drop in pipe flow by Smits and Zagarola [Phys. Fluids 10, 1045 (1998)] within the scaling theory of Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000)], developed in the context of thermal convection. The main idea is to split the energy dissipation into contributions
from a boundary layer and the turbulent bulk. This ansatz can account for the observed scaling in both cases if it is assumed
that the internal wind velocity introduced through the rotational or pressure forcing is related to the external (imposed) velocity U, by with and for the Taylor-Couette (U inner cylinder velocity) and pipe flow (U mean flow velocity) case, respectively. In contrast to the Rayleigh-Bénard case the scaling exponents cannot (yet) be derived
from the dynamical equations.
Received 9 September 2000 相似文献
12.
Feng and Weinbaum [J. Fluid Mech. 422, 282 (2000)]] have shown that there is a remarkable dynamic similarity between a red cell gliding on the endothelial surface glycocalyx and a human snowboarding on fresh powder although they differ in mass by 10(15). The lift forces in each case are 4 orders of magnitude greater than classical lubrication theory. Herein we report the first measurements of the pore pressures generated on the time scale of snowboarding and show a feasibility of designing a train that can glide on a track whose permeability and elastic properties are similar to goose down. 相似文献
13.
Robey HF Perry TS Klein RI Kane JO Greenough JA Boehly TR 《Physical review letters》2002,89(8):085001
Laser-driven experiments are described which probe the interaction of a very strong shock with a spherical density inhomogeneity. The interaction is viewed from two orthogonal directions enabling visualization of both the initial distortion of the sphere into a double vortex ring structure as well as the onset of an azimuthal instability that ultimately results in the three-dimensional breakup of the ring. The experimental results are compared with 3D numerical simulations and are shown to be in remarkable agreement with the incompressible theory of Widnall et al. [J. Fluid Mech. 66, 35 (1974)]. 相似文献
14.
We report the first detailed experimental observation of the Batchelor regime [G. K. Batchelor, J. Fluid. Mech. 5, 113 (1959)], in which a passive scalar is dispersed by a large scale strain, at high Peclet numbers. The observation is performed in a controlled two-dimensional flow, forced at large scale, in conditions where a direct enstrophy cascade develops [J. Paret, M.-C. Jullien, and P. Tabeling, Phys. Rev. Lett. 83, 3418 (1999)]. The expected k(-1) spectrum is observed, along with exponential tails for the distributions of the concentration and concentration increments and logarithmlike behavior for the structure functions. These observations, confirmed by using simulated particles, provide a support to the theory. 相似文献
15.
By using the Onsager principle of minimum energy dissipation, the hydrodynamic boundary conditions at the fluid–solid interface are shown to be the natural emergent behavior of microscopic interactions that lead to the interfacial tension and the tangential friction at the fluid–solid interface [T. Qian, C. Qiu, P. Sheng, J. Fluid Mech. 611 (2008) 333]. This is satisfying because the equations of motion, e.g., the Stokes equation, and the hydrodynamic boundary conditions can now be derived from a unified framework. The resulting continuum hydrodynamic formulation yields predictions for immiscible two-phase flows that are in quantitative agreement with molecular dynamic simulations. In particular, the classical problem of the moving contact line is resolved. We also show results on the moving contact line over chemically patterned surfaces which exhibit striking nanoscale characteristics as well as sub-quadratic dependence of the moving contact line dissipation on its average velocity. 相似文献
16.
The scaling law for the threshold amplitude of perturbations to initiate a transition in subcritical plane Poiseuille flow as a function of the Reynolds number is demonstrated experimentally. The disturbances are introduced through an almost streamwise independent slot drilled at the bottom wall of a horizontal air-channel flow. Following the two stages of transition, linear transient growth and nonlinear secondary instability, it is found that the normalized critical injection rate (v0) scales with the Reynolds number (R) as v0 approximately R-3/2. This scaling law agrees with the theoretical predictions of Chapman [J. Fluid Mech. 451, 34 (2002).]. 相似文献
17.
We address the question of stability of the so-called S-type Riemann ellipsoids, i.e. a family of Euler flows in gravitational equilibrium with the vorticity and background rotation aligned along the principal axis perpendicular to the flow. The Riemann ellipsoids are the simplest models of self-gravitating, tidally deformed stars in binary systems, with the ellipticity of the flow modelling the tidal deformation. By the use of the WKB theory we show that mathematically the problem of stability of Riemann ellipsoids with respect to short-wavelength perturbations can be reduced to the problem of magneto-elliptic instability in rotating systems, studied previously by Mizerski and Bajer [K.A. Mizerski, K. Bajer, The magneto-elliptic instability of rotating systems, J. Fluid Mech. 632 (2009) 401-430]. In other words the equations describing the evolution of short-wavelength perturbations of the Riemann ellipsoids considered in Lagrangian variables are the same as those for the evolution of the magneto-elliptic-rotational (MER) waves in unbounded domain. This allowed us to use the most unstable MER eigenmodes found in Mizerski et al. [K.A. Mizerski, K. Bajer, H.K. Moffatt, The α-effect associated with elliptical instability, J. Fluid Mech., 2010 (in preparation)] to provide an estimate of the characteristic tidal synchronization time in binary star systems. We use the idea of Tassoul [J.-L. Tassoul, On synchronization in early-type binaries, Astrophys. J. 322 (1987) 856-861] and that the interactions between perturbations significantly increase the effective viscosity and hence the energy dissipation in an Ekman-type boundary layer at the surface of the star. The results obtained suggest that if the magnetic field generated by (say) the secondary component of a binary system is strong enough to affect the flow dynamics in the primary, non-magnetized component, the characteristic tidal synchronization time can be significantly reduced. 相似文献
18.
We show [J. Fluid Mech. 592, 447 (2007)] that swapping (reversing) trajectories in confined suspension flows prevent collisions between particles approaching each other in adjacent streamlines. Here we demonstrate that by inducing layering this hydrodynamic mechanism changes the microstructure of suspensions in a confined Couette flow. Layers occur either in the near-wall regions or span the whole channel width, depending on the strength of the swapping-trajectory effect. While our theory focuses on dilute suspensions, we postulate that this new hydrodynamic mechanism controls the formation of a layered microstructure in a wide range of densities. 相似文献
19.
Numerical Simulation for thermohaline multiple equilibrant system in non—rectangular domains
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In this paper, incompressible, double-diffusive convection is simulated
using finite-difference schemes. The Navier--Stokes equations are
expressed in terms of stream function and vorticity. Because of
the existence of large velocity, temperature and salinity gradients
in boundary layers, a boundary-fitted coordinate system is used
to concentrate the grid points near the wall and fit complex
boundaries. The finite-difference methods used include the high-order
accurate upwind difference scheme. It is
shown that the scheme is a good candidate for direct simulations of
double-diffusive convection flows. The proposed method is first
applied to symmetry breaking and overturning states in
thermohaline-driven flows in trapezoid basins. The basic phenomena
agree well with those by Dijkstra and Molemaker (1997 {\em J. Fluid
Mech.} {\bf 331} 169)
and Quon and Ghil (1992 {\em J. Fluid Mech.} {\bf 245} 449), but symmetry breaking and
overturning states can occur in an asymmetric geometrical region
without perturbations. Then the method is applied to double-diffusive
convections in a cavity with opposing horizontal temperature and
concentration gradients at large thermal ($Rt$), solutal ($Rs$)
Rayleigh numbers and Lewis number. There are three straight sides
and a sine curve side in the cavity. Basically, numerical results
are in agreement with those of Lee and Hyun (1990 {\em Int. J. Heat
Mass Transfer} {\bf 33} 1619) qualitatively, but eddies mixing in the
top left-hand corner near the curved wall affects the layered structure. 相似文献
20.
Fellah ZE Fellah M Lauriks W Depollier C 《The Journal of the Acoustical Society of America》2003,113(1):61-72
This paper provides a temporal model of the direct and inverse scattering problem for the propagation of transient ultrasonic waves in a homogeneous isotropic slab of porous material having a rigid frame. This new time domain model of wave propagation takes into account the viscous and thermal losses of the medium as described by the model of Johnson et al. [D. L. Johnson, J. Koplik, and R. Dashen, J. Fluid. Mech. 176, 379 (1987)] and Allard [J. F. Allard (Chapman and Hall, London, 1993)] modified by a fractional calculus based method applied in the time domain. This paper is devoted to the analytical calculus of acoustic field in a slab of porous material. The main result is the derivation of the expression of the scattering operators (reflection and transmission) which are the responses of the medium to an incident acoustic pulse. In this model the reflection operator is the sum of two contributions: the first interface and the bulk of the medium. Experimental and numerical results are given as a validation of our model. 相似文献