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81.
82.
In this work we report theoretical and numerical results on convection in a viscoelastic binary mixture under rotation for realistic rigid-rigid boundary conditions. We focus our analysis in the DNA aqueous suspensions. Instability thresholds for oscillatory convection are calculated. Finally, we analyze the stabilizing effect for the onset of convection. 相似文献
83.
K. Gersten M. Grobel H. Klick W. Merzkirch 《International Journal of Heat and Fluid Flow》1991,12(4):331-335
Theoretical and experimental studies of flow separation in laminal natural convection are presented. Since classical boundary-layer theory cannot determine separation on curved walls in natural convection, two extensions of the classical boundary-layer theory are discussed: boundary-layer theory of higher order and double-deck theory. Both theories are applied to experiments on a vertical flat plate with humps. 相似文献
84.
In the case of convection dominated problems, multigrid methods require an appropriate smoothing to ensure robustness. As a first approach we discuss a Gauss–Seidel smoothing with a correct numbering of the unknowns and if necessary a special block partitioning. Numerical experiments show that, in the case of general convection directions, the multigrid algorithms obtained in this way have the same properties as in the model situation. If the graph arising from the convection part is acyclic, we describe a numbering algorithm which is valid for all spatial dimensions. Cycles give rise to special blocks for a blockwise Gauss–Seidel smoothing. We describe an algorithm for the two-dimensional case. The proposed algorithm requires a computational work of optimal order (linear in the size of the problem). © 1997 by John Wiley & Sons, Ltd. 相似文献
85.
The linear stability analysis of the natural convection in a rectangular tilted infinite cavity filled with a Boussinesq fluid subject to Coriolis force is presented. The bottom and top surfaces have fixed temperatures. Both unstable and stable thermal conditions are studied (heated from below and heated from above respectively). The rotation axis passes through the center and it is orthogonal to the hot and cold surfaces. The stability equations were solved using the Tau–Chebyshev spectral method. The critical Rayleigh number and critical wave number were obtained for several rotation rates and different orientation of convective oblique rolls in a range of inclination of the cavity from 0 to 120 degrees. The stability analysis show that rotation rate affects the basic velocity profile, onset of convection, wave number and critical orientation of convective rolls. 相似文献
86.
An experimental study of natural convection in a parallelepipedal enclosure induced by a single vertical wall is described. The upper half of this wall was warm and the lower half cold. The other enclosure walls were insulated. The temperature and flow measurements were performed in the high Rayleigh number regime (1010<Ra<5×1010) by using water as the working fluid. The Rayleigh number was based on the enclosure height and the temperature difference between the warm and the cold part of the driving wall. The flow field featured two flat cells, one filled with warm fluid along the top horizontal wall, and the other filled with cold fluid along the bottom horizontal wall. Each of these cells was surrounded by an additional cell as tall as half the enclosure height. The above flow structure prohibited extensive thermal contact between warm and cold fluid, thus limiting the role of convection on the heat transfer process in the cavity. The findings of this study differ significantly from the findings of previous studies based on the ‘classical’ enclosure model possessing two isothermal vertical walls, the one warm and the other cold, and support the view that the use of ‘more realistic‘ temperature boundary conditions in enclosure natural convection needs careful examination. 相似文献
87.
88.
Until now, an unconditional nonlinear energy stability analysis for thermal convection according to Navier-Stokes theory had not been developed for the case in which the viscosity depends on the temperature in a quadratic manner such that the viscosity has a maximum. We analyse here a model of non-Newtonian fluid behaviour that allows us to develop an unconditional analysis directly when the quadratic viscosity relation is allowed. By unconditional, we mean that the nonlinear stability so obtained holds for arbitrarily large perturbations of the initial data. The nonlinear stability boundaries derived herein are sharp when compared with the linear instability thresholds.Received: 9 April 2003, Accepted: 28 April 2003, Published online: 12 December 2003PACS:
03.50.De, 04.20.-q, 42.65.-kCorrespondence to B. Straughan 相似文献
89.
Based on a modified-Darcy–Brinkman–Maxwell model, stability analysis of a horizontal layer of Maxwell fluid in a porous medium heated from below is performed. By solving the eigenvalue problems, the critical Rayleigh number, wave number and frequency for overstability are determined. It is found that the critical Rayleigh number for overstability decreases as the relaxation time increases and the elasticity of a Maxwell fluid has a destabilizing effect on the fluid layer in porous media. On the other hand, the critical Rayleigh number for overstability increases by increasing the porous parameter which acts to stabilize the system. In limiting cases, some previous results for viscoelastic fluids in nonporous media are recovered from our results. 相似文献
90.
Dingfang Li Xiaofeng Wang & Hui Feng 《advances in applied mathematics and mechanics.》2013,5(1):55-77
A fully higher-order compact (HOC) finite difference scheme on the
9-point two-dimensional (2D) stencil is formulated for solving the
steady-state laminar mixed convection flow in a lid-driven inclined
square enclosure filled with water-$Al_2O_3$ nanofluid. Two
cases are considered depending on the direction of temperature
gradient imposed (Case I, top and bottom; Case II, left and right).
The developed equations are given in terms of the stream
function-vorticity formulation and are non-dimensionalized and then
solved numerically by a fourth-order accurate compact finite
difference method. Unlike other compact solution procedure in
literature for this physical configuration, the present method is
fully compact and fully higher-order accurate. The fluid flow, heat
transfer and heat transport characteristics were illustrated by
streamlines, isotherms and averaged Nusselt number. Comparisons with
previously published work are performed and found to be in excellent
agreement. A parametric study is conducted and a set of graphical
results is presented and discussed to elucidate that significant
heat transfer enhancement can be obtained due to the presence of
nanoparticles and that this is accentuated by inclination of the
enclosure at moderate and large Richardson numbers. 相似文献