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1.
D. B. Ingham 《Acta Mechanica》1982,42(1-2):111-122
Summary In this paper it is shown, using a numerical technique, that axially-symmetric solutions of the boundary layer equations which describe the rotating flow near the equator of a rotating sphere are not unique. In certain regimes it is found that at least three possible solutions are possible. When the sphere and fluid rotate with almost the same angular velocity it is shown that the approach to solid body rotation is a non linear process.With 5 Figures  相似文献   

2.
The axisymmetric flow due to a uniform stream at infinity past a slowly rotating sphere in a viscous incompressible rotating fluid is studied and the results are presented mostly in the form of graphs of the streamlines. A region of reversed flow and vortex formation is found to occur near the front or rear stagnation points under certain conditions depending upon the speed of the uniform stream at infinity, the radius of the sphere and the angular velocity of the sphere. The fluid may rotate in the same or opposite directions.  相似文献   

3.
The structure of rimming flow in a horizontal rotating cylinder subjected to vibration is experimentally investigated. Under vibration liquid performs oscillations. In the resonant domain oscillations have a form of progressive two-dimensional azimuth wave which generates averaged flow in the direction of its propagation. It is found that the plane motion is unstable to the spatially periodic vortical flow appearance. The transition to the vortical flow is determined by the oscillatory liquid flow instability in viscous Stokes layer near cylindrical wall. The threshold of 2D flow instability and the structure of overcritical flows in a wide range of dimensionless parameters are investigated.  相似文献   

4.
An exact solution of the unsteady Navier-Stokes equations is obtained for the flow due to non-coaxial rotations of a porous disk, executing non-torsional oscillations in its own plane, and a fluid at infinity. It is shown that the infinite number of solutions existing for a flow confined between two disks reduce to a single unique solution in the case of a single disk. The adjustment of the unsteady flow near the rotating disk to the flow at infinity rotating about a different axis is explained.  相似文献   

5.
Results are given of a theoretical and experimental study of a convective mass exchange in the regime of limiting diffusion current toward the polar surface of a rotating sphere, for a creeping and boundary-layer type of flow near the surface.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 3, pp. 448–456, September, 1982.  相似文献   

6.
Peristaltic pumping by an infinite train of sinusoidal waves in the walls of a two-dimensional tube is investigated theoretically when the inertial and streamline-curvature effects are moderate but not negligible as it is the case for roller pumps and the gastrointestinal tract. It is found that the pumping performance increases with increasing wall curvature and is decreased by inertial effects except at high squeeze. As in the inertia-free, infinite wavelength case there is a backwards flow (reflux) near the moving walls which is enhanced by both the inertial and curvature effects. Under certain conditions, there are boluses of fluid moving at the wave speed as if they were trapped by the wave. The range of this trapping is decreased by inertial effects and increased by curvature effects.  相似文献   

7.
A Monte Carlo simulation is used to make a detailed analysis of the nonequilibrium zone formed near the surface of a condensing sphere. Significant directional anisotropy of the temperature was observed. It was established that the nonequilibrium near an absolutely black sphere is responsible for the difference between the calculated values of the specific mass flow in comparison with the published data obtained assuming little difference between the vapor state at infinity and temperature saturation conditions at the surface of the sphere. Pis’ma Zh. Tekh. Fiz. 25, 43–48 (January 26, 1999)  相似文献   

8.
It is pointed out that in a reaction-diffusion system near a chiral symmetry-breaking instability, a weak drift term in the diffusion law can induce a systematic selection between macroscopic three-dimensional patterns of opposite chirality. When the cause of the drift term is an external field, the orientation of the field with respect to the system determines the final chiral choice. The possible appearance of a drift term in the diffusion law, arising from the intrinsic asymmetry of the underlying material is also considered. In a one-dimensional system with periodic boundary conditions it is shown that the drift term may account for systematic selection between waves rotating in opposite directions  相似文献   

9.
The centrifugal instability of power law fluid flow when the fluid fills the gap between two rotating concentric cylinders of infinite length is addressed. The instability of the circular Couette flow is determined via linear stability analysis. In the narrow gap case, the critical Taylor number is determined analytically, while in the general gap case, a finite-difference numerical method is employed. The results are shown to be in agreement with existing theoretical and experimental findings. The super-critical flow is investigated by means of a weakly non-linear analysis method. The Taylor-vortex flow (the secondary stable flow) is obtained. The instability of this flow is determined as we present the critical Taylor number when the Taylor vortices begin to exhibit a waviness in the azimuth  相似文献   

10.
The development of instability in a flow generated in a cylindrical cavity with a rotating endwall has been studied. Both possible scenarios of the development of instability, according to which the amplitude of velocity pulsation grows or decays with increasing swirl of the flow, have been observed for the first time. It is established that these processes depend on the appearance of secondary perturbations and on their relative frequency.  相似文献   

11.
In this article, we have investigated the onset of instability in the flow of the micropolar fluid between two rotating concentric cylinders and the flow in a curved channel, under small gap approximation. The solution of the eigenvalue problems, governing the onset of instability, are obtained by using the Shooting Method. It is seen that the flows are stable when the micropolar elements are present in the fluid.  相似文献   

12.
In this study, a direct numerical simulation of the fluid flow and heat transfer characteristics of separation and reattachment flow at a backward-facing step is presented. A computer program of FORTRAN code is used to solve the governing equations according to finite volume method. The effects of the Reynolds number and expansion ratio on the fluid flow and heat transfer characteristics are investigated. The size of the primary recirculation zone increases with the reduction of expansion ratio and the fluctuation of isotherms increased with the increase of Reynolds number. The periodic characteristics and the dissimilarity between Nu and Cf appear in the transitional flow regime. The rotating fluids in the reattachment region increase the flow instability and the interchange of the hot and cold fluids increases heat transfer instability. The combined effects of flow instability and heat transfer instability play an important role in the formation of the dissimilarity between Nu and Cf.  相似文献   

13.
Summary The boundary-layer growth near the equator of an impulsively rotated sphere is considered numerically and analytically. The numerical work is highly suggestive of the presence of a singularity at a finite time at which two of the velocity components and the swirl displacement thickness become infinite. Details of an analytic investigation are presented which is consistent with the gross features of the numerical results. Brief consideration is also given to the flow near the equators of impulsively rotated spheroids and it is shown that the relevant boundary-layer equations for this class of bodies can be written in the same form as those for the sphere.  相似文献   

14.
An analysis about the effects of various metamaterial coatings and background media upon the gain characteristics of a slotted sphere is presented using numerical simulations. It is found that the gain characteristics of a coated slotted sphere can be controlled by varying the electromagnetic parameters of coatings and background media. It is studied that the thickness of different coating layers has a significant effect upon the gain in the forward direction. It is further investigated that a double negative metamaterial coating can be used to greatly enhance the forward direction gain for certain values of the permittivity and the permeability. It is also shown that single near zero and double near zero background media enhance the forward direction gain of a dielectric-coated slotted sphere and reduce the gains for angles closer to polar directions as compared to the free space background.  相似文献   

15.
Summary A numerical study of laminar plane Couette flow subjected to a steady spanwise rotation is conducted. The full nonlinear Navier-Stokes equations in a steadily rotating framework are solved by a finite difference method for a long, large-aspect-ratio rectangular channel where the outer wall moves at a constant velocity. In this manner, nonlinear and wall end effects which are present in any real laboratory Couette flow experiment are taken into account. The computations demonstrate the existence of a roll instability, at intermediate rotation rates, when the Reynolds number exceeds a critical value of 42. The associated secondary flow in the form of longitudinal rolls is shown to have a severe distortional effect on the primary axial velocity in the interior of the channel which is not linear like its counterpart in an inertial framework. Comparisons are made with previously conducted linear stability analyses as well as with other analogous numerical and experimental studies.With 15 Figures  相似文献   

16.
We study the laminar boundary-layer flow over a general spheroid rotating in otherwise still fluid. In particular, we distinguish between prolate and oblate spheroids and use an appropriate spheroidal coordinate system in each case. An eccentricity parameter e is used to distinguish particular bodies within the oblate or prolate families and the laminar-flow equations are established for each family with e as a parameter. In each case, setting e = 0 reduces the equations to those already established in the literature for the rotating sphere. We begin by solving the laminar-flow equations at each latitude using a series-solution approximation. A comparison is then made to solutions obtained from an accurate numerical method. The two solutions are found to agree well for a large range of latitudes and eccentricities, and at these locations the series solution is to be preferred due to its simplicity and ease of computation. A discussion of the resulting flows is given with particular emphasis on the implications for their hydrodynamic stability. Their stability characteristics are expected to be very similar to those over the rotating sphere as already studied in the literature.  相似文献   

17.
Abstract

In this paper the turbulent flow generated in a cylindrical container by a low-frequency rotating magnetic field is considered. The rotational part of the electromagnetic body force is steady and axisymmetric, driving an azimuthal swirl flow. It is shown that curvature effects are negligible near the wall of the containing vessel and consequently the velocity profile in that region has the standard logarithmic form. Extrapolating this profile to the core allows an estimate of the core angular velocity to be made. This estimate is consistent with published experimental data and with the results of a more complex two-parameter closure model.

MST/207  相似文献   

18.
The stability of a family of boundary-layer flows, which includes the von Kármán, B?dewadt and Ekman flows for a rotating incompressible fluid between a rotating disc and a stationary lid, is investigated. Numerical computations with the use of a spectral method are carried out to analyse absolute and convective instability. It is shown that the stability of the system is enhanced with a decrease in distance between the disc and the lid.  相似文献   

19.
For the first time, we have calculated the attraction force, frictional torque, and heating rate that are caused by fluctuation-electromagnetic interaction of a small spherical particle uniformly rotating at a constant angular velocity near a heated surface. Closed analytical formulas are obtained for these quantities. It is shown that the stopping time of a particle rotating in the near field of the surface is much less than the stopping time under rotation in vacuum space.  相似文献   

20.
Itiro Tani 《Sadhana》1981,4(2):219-238
A review is made in this paper of the three-dimensional nature of instability leading to transition in a two-dimensional flow on a flat plate (Blasius boundary layer) or between parallel plates (plane Poiseuille flow), with additional reference to the flow on a concave wall. Instability and transition in a three-dimensional boundary layer are then reviewed, with particular attention to the flow due to a rotating disk and the flow perturbed by a three-dimensional roughness element on a flat plate. The growth of a turbulent spot is discussed as a phenomenon exhibiting a similar feature of instability. Only the flow of an incompressible fluid is considered.  相似文献   

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