共查询到20条相似文献,搜索用时 15 毫秒
1.
Dielectric-liquid flows in narrow channels with walls composed of different dielectrics are investigated experimentally. It is revealed that at a certain flow velocity, as a result of electrization, on the interface between the dielectrics the liquid begins to glow. The glow is discrete in the form of frequent pulses and is accompanied by electromagnetic noise on the radio-frequency range. It is shown that with decrease in the channel thickness the glow appears at smaller flow velocities. The glow is accompanied by heating of the liquid in the wall region to temperatures that may reach several tens of degrees. The electrization potential reaches more than 100 kV. The mechanisms of electrization and liquid glow are discussed. 相似文献
2.
We study the stability of the flow which forms in a plane channel with influx of an incompressible viscous fluid through its porous parallel walls. Under certain assumptions the study of the stability reduces to the solution of modified Orr-Sommerfeld equation accounting for the transverse component of the main-flow velocity. As a result of numerical integration of this equation we find the dependence of the local critical Reynolds number on the blowing Reynolds number R0, which may be defined by two factors: the variation of the longitudinal velocity profile with R0 and the presence of the transverse velocity component. A qualitative comparison is made of the computational results with experimental data on transition from laminar to turbulent flow regimes in channels with porous walls, which confirms that it is necessary to take into account the effect of the transverse component of the main-flow velocity on the main-flow stability in the problem in question.Flows in channels with porous walls are of interest for hydrodynamic stability theory in view of the fact that they can be described by the exact solutions of the Navier-Stokes equations by analogy with the known Poiseuille and Couette flows. However, in contrast with the latter, the flows in channels with porous walls (studies in [1], for example) will be nonparallel.The theory of hydrodynamic stability of parallel flows has frequently been applied to nonparallel flows (in the boundary layer, for example). In so doing the nonparallel nature of the flow has been taken into account only by varying the longitudinal velocity component profiles. A study was made in [2, 3] of the effect of the transverse component of the main flow on its stability. In the case of the boundary layer in a compressible gas, a considerable influence of the transverse velocity component on the critical Reynolds number was found in [2] and confirmed experimentally. A strong influence of the transverse velocity component on the instability region was also found in [3] in a study of the flow stability in a boundary layer with suction for an incompressible fluid. 相似文献
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In the flow of a suspension in a channel with porous walls, when the size of particles of a suspended phase is much less than the width of the channel but greatly exceeds the size of the pores (in particular, in the flow of blood in the plasma separator used in an artificial kidney system [1, 2]), phenomena are observed which apparently cannot be satisfactorily explained by means of the well-known solutions of problems on the motion of a Newtonian fluid [3]. For example, the flow rate of the liquid phase of the suspension through the walls depends on the velocity of the main flow and does not depend on the pressure drop on the wall at fairly high values of it [1, 2]. The present study gives below the formulation and an approximate solution, which explains this effect, of the problem of an incompressible two-phase suspension in a long slit with porous walls which are impermeable in relation to the suspended phase and through which the liquid phase is pumped. Certain effects are taken into account which are caused by the high volume concentration of the suspended phase.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 37–43, November–December, 1987. 相似文献
5.
O. V. Ilyin 《Fluid Dynamics》1994,29(4):458-464
A general solution is obtained for the boundary value problem of designing a thin airfoil in a channel with permeable walls
from the given pressure distribution. A suitable choice of permeability coefficients makes it possible to construct a thin
airfoil in a channel with impermeable walls, in a jet, etc. The effect of the wall permeability on the shape of the airfoil
is studied.
Cheboksary. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 28–34, July–August,
1994. 相似文献
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Kiran Bhaganagar Vejapong Juttijudata 《Theoretical and Computational Fluid Dynamics》2012,26(6):583-589
This brief communication quantifies the time-events that contribute to the dynamics of wall-bounded flows with rough walls. Lumley’s Proper Orthogonal Decomposition (POD) methodology has been used to extract the energetic modes of the flow. We have used the concept of entropy, a representation of lack of organization in the flow, to represent the extent of spread of turbulent kinetic energy to higher modes. The rough-wall dynamics is dominated by fast activity (short time period) propagating modes and slow activity (long time period) roll modes. A single dominant timescale has been captured for all the propagating modes in flows over smooth walls; multiple dominant timescales representing various vortex shedding events are captured for rough walls. Variable-interval time averaging technique has been used to obtain the bursting frequency. The bursting frequency of rough-wall turbulence is higher compared to smooth-wall turbulence, suggesting that roughness enhances turbulence production activity. Another insightful observation for rough walls revealed by our study is that the vortex shedding frequency of roughness elements is much higher compared to the bursting frequency of rough-wall turbulence. POD provides a straightforward method to extract the natural frequency of shed vortices due to roughness, an important dynamical activity in rough-wall turbulent boundary layers. 相似文献
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Sokrates Tsangaris Christos Nikas Grigorios TsangarisPanagiotis Neofytou 《ournal of non Newtonian Fluid Mechanics》2007
In the present paper the flow of a Bingham fluid between two parallel porous walls is studied. One of the walls moves with constant velocity parallel to the other, which is fixed, while a longitudinal pressure gradient exists, as well as a transverse flow field due the porosity of the walls. An exact analytical solution is given for the u-velocity field, which has four different forms depending on the values of the three dimensionless parameters, which are the Bingham, Couette and Reynolds numbers. 相似文献
10.
Analytic expressions for the complex flow potential are obtained in the linear formulation in the neighborhood of a plate at a small angle of incidence and near porous channel walls. The general solution includes the limiting cases of a plate in a channel with impermeable walls and in a jet. Numerical results concerning the effect of porosity on the flow geometry in the neighborhood of the plate and the channel walls are presented. The disturbed-flow velocity distributions along the channel walls and the flow rate of the fluid sinking at infinity are obtained.Cheboksary. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 13–19, July–August, 1995. 相似文献
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K.K. Mondal 《International Journal of Non》2005,40(1):69-81
The paper presents the longitudinal dispersion of passive tracer molecules released in an incompressible viscous fluid flowing through a channel with reactive walls under the action of a periodic pressure gradient. A finite-difference implicit scheme is adopted to solve the unsteady advection-diffusion equation based on the Aris-Barton method of moments for all time period. Here it is shown how the spreading of tracers is influenced by the shear flow, lateral diffusion about its mean position due to the action of absorption at both the walls. The analysis has been performed for three different cases: steady, periodic and the combined effect of steady and periodic currents, separately. The results show that for all cases the dispersion coefficient asymptotically reaches a stationary state after a certain critical time and it achieves a stationary state at earlier instant of time, when absorption at the walls increases. The axial distributions of mean concentration are determined from the first four central moments by using Hermite polynomial representation for all three different flow velocities. 相似文献
13.
Arbitrary three-dimensional perturbations are considered. It is established that as the compliance of the walls increases, oblique waves become the most dangerous, which essentially differentiates the system in question from Poiseuille flow in a rigid channel. The flow stability is analyzed over a broad interval of values of the elasticity parameter overlapping the values for real materials.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 67–72, May–June, 1988. 相似文献
14.
An experimental study was made of the hydrodynamics of a film of liquid flowing over the external surface of a cylindrical channel, in the range of film-flow Reynolds numbers R = / = 120–7200 ( is the mass irrigation density; is the dynamic viscosity) at different distances from the inlet (x = 1–19 m).Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 128–135, January–February, 1973. 相似文献
15.
Summary The steady laminar flow of a viscous incompressible fluid through a two-dimensional channel, having fluid sucked or injected with different velocities through its uniformly porous parallel walls is considered. A solution for small suction Reynolds number has been given by the authors in a previous paper. The purpose of this paper is to present a solution valid for large Reynolds numbers for the cases of (i) suction at both walls, and (ii) suction at one wall and injection at the other. A technique of matching outer and inner expansions is used to obtain an asymptotic solution for both of these cases. Further a perturbation solution for the case of suction at one wall and injection at the other is obtained by choosing the difference between two wall velocities as the perturbation parameter. Both asymptotic and perturbation solutions are confirmed by exact numerical solutions. As expected, the resulting solutions show the presence of the usual suction boundary layers in both types of flow considered in this paper. 相似文献
16.
Laminar flow in a rotating rectangular channel with suction through one or more of the permeable walls is studied. The conditions
under which a two-dimensional formulation of the flow core calculations is possible are discussed and the corresponding problem
is formulated. Calculation results illustrating the combined effect of suction and rotation about the transverse axis are
presented for a channel with a stopped end.
Leningrad. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 30–34, September–October,
1988. 相似文献
17.
Frdric Grisch Guy-Alexandre Grandin Dominique Messina Brigitte Attal-Trtout 《Comptes Rendus Mecanique》2009,337(6-7):504-516
Detailed experimental investigation of a non-equilibrium nanosecond pulsed discharge in premixed CH4/air mixtures at atmospheric pressure has been carried out. The experiments demonstrated significant reductions in ignition delay and increased lean burn capability relative to conventional spark ignition. Advanced laser diagnostics have been used to identify the physical processes which lead to these improvements. The electron temperature and density properties were measured using laser Thomson scattering (LTS). Temperature measurements were performed using N2 CARS thermometry to quantify the energy transfer in the gas mixture. Effect of the discharge on the local temperature shows the existence of the ignition of the gas mixture for equivalence ratio between 0.7 and 1.3. Fast development of a flame kernel is then observed. The experiment also shows that the flame can be sustained above the discharge due the repetitive ignition of the flame at the plasma repetition rate. Finally, OH and CH PLIF experiments were performed to confirm the large OH and CH streamer-induced production over the discharge volume. To cite this article: F. Grisch et al., C. R. Mecanique 337 (2009). 相似文献
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The mechanism of the overheating instability of magnetohydrodynamic flows is as follows. if the electrical conductivity of the medium depends on the temperature, then a small local increase in temperature may lead, under specific conditions, to an increase in liberation of Joule heat energy, to a further temperature rise, and so to instability.The overheating instability has been studied before (1, 2) for a unifrom unperturbed temperature and without account for the effect of the boundaries of the region. It has been discovered that the growth increment of the disturbances increases as the wavelength increases. However, it is clear that heat conduction through the boundaries of the region occupied by the conducting medium may effect the development of perturbations, primarily of long wavelength perturbations. Below we will examine the simplest problem of the stability of temperature distribution for an electric discharge in a gas between two planes. 相似文献
20.
Detailed quantitative maps of the heat transfer distribution in a square channel with angled rib turbulators are measured by means of infrared (IR) thermography associated with the heated-thin-foil technique. Air flows in the channel where square ribs are mounted on two opposite walls at an angle of either 30° or 45° with respect to the duct axis. Two rib pitches, two different rib arrangements and two heating conditions are investigated. Results are presented in terms of local and averaged Nusselt numbers, which are normalised with the classical Dittus and Boelter correlation, for three different Reynolds numbers. 相似文献