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1.
The effect of unipolar injection of charges on the electroconvective motion of a weakly conducting liquid in a plane-parallel electrode system is investigated. By means of a numerical experiment it is confirmed that the crisis in the stability of a plane layer of weakly conducting liquid with unipolar injection conductivity depends significantly on the electrochemical processes in the electrode layer. A~dependence of the unipolar charge injection on the initial conductivity for a solution of molecular iodine in transformer oil is obtained. 相似文献
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In this work, a series of direct numerical simulations are conducted to study the effect of wall normal spanwise homogeneous wall actuation on a turbulent boundary layer. The moving boundary is represented by a boundary data immersion technique. A parametric study was performed, varying the actuator length, the wall normal actuation amplitude and the actuation frequency. It was found that localized actuation, relying only on wall motion instead of requiring a plenum in the case of synthetic jets, generated a net momentum flux jet affecting the flow not only in the immediate vicinity of the actuator but also for a significant distance downstream. The cases with an actuator velocity of \( u^{+}_{act}=?20.1 \) showed a particularly pronounced effect on the boundary layer and resulted in a recirculation region. 相似文献
3.
The effect of a standing acoustic wave on the development of long-wave convective perturbations in a horizontal layer with thermally insulated boundaries is investigated. The main two-dimensional flow is determined. A nonlinear amplitude equation with spatially-periodic coefficients is derived for investigating the stability of the main flow and secondary convection flows in the neighborhood of the stability threshold. The intensity of the acoustic field is assumed to be low. It is shown that the acoustic action leads to destabilization of the layer. Plane and three-dimensional perturbations are critical at large and small Prandtl numbers, respectively. Nonlinear one-dimensional steady-state solutions of the amplitude equation are obtained and their stability is investigated. 相似文献
4.
We are interested in the large-time behavior of a stationary shock layer in the presence of a boundary effect. It is shown
that the stationary shock propagates away from the boundary with speed inversely proportional to the time . Consequently, the location of the wave front is of order . We show therefore that the zero-viscosity and time-asymptotic limits do not commute. Our analysis involves detailed point-wise
estimates, which allow us to trace the shock.
(Accepted April 16, 1996) 相似文献
5.
IntroductionTheMixinglayeriscommonlyencounteredinvariouschemicalprocesses .Itisthereforesignificanttostudythebehaviorsofcoherentstructuresinamixinglayerinordertopredictandcontroltheevolutionoftheflow ,thenimprovethemixingandchemicalreactionefficiency .S… 相似文献
6.
含ER流体板结构的振动特性研究 总被引:8,自引:0,他引:8
本文制作了含电流变体夹层梁和模拟飞机蒙皮结构的含电流变体加筋层合板,采用响应幅频法,测试了在不同电场强度梁和层合加筋板结构各阶固有频率和振幅的变化;并着重测试了加筋层合板结构在改变板材料、电流变体作用面积等条件时各阶频响特性的变化。实验结果表明,随着电场强度的增加,夹层梁的频响特性有很大变化;而层合板的固有频率变化不大,但振幅却有显著变化,其中铝-层合加筋板的频响幅值的变化率达到50.1%。 相似文献
7.
柔性壁面湍流边界层相干结构控制的实验研究 总被引:3,自引:0,他引:3
本文利用热膜测速技术对刚性壁面和柔性壁面湍流边界层的流向速度分量进行了实验测量,首先研究了柔性壁面对平均速度分布和湍流度分布的影响,结果表明:柔性壁面的边界层速度分布在对数律层向上有所平移,缓冲层加厚,具有一般的壁面减阻特征;而柔性壁的湍流度比刚性壁的湍流度要低,分布也更为平坦。然后综合运用自相关法和条件采样技术研究了湍流近壁区的相干结构,结果表明:刚性壁自相关曲线的第二峰值出现的时间比柔性壁的短,柔性壁的猝发频率比刚性壁的低许多。实验结果表明柔性壁面具有一定的减阻作用。 相似文献
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10.
E. A. Ryabitskii 《Fluid Dynamics》2001,36(3):341-348
Within a linear formulation, the thermocapillary instability of equilibrium of a cylindrical layer of heat-conducting viscous fluid in the presence of a radial temperature gradient is investigated with respect to arbitrary disturbances. It is shown that the Rayleigh instability mechanism results in the appearance of monotonous disturbances of a new type. For steady disturbances, the neutral curve is split into two separate segments, each corresponding to its own type of disturbances. For a deformable free boundary, new oscillating disturbances in the form of surface waves develop. It is found that, in the case of axial symmetry, the behavior of these disturbances completely coincides with the oscillating disturbance behavior in a plane layer. 相似文献
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Transition to turbulence in the boundary layer on a flat plate is investigated numerically for an incompressible fluid flow with a given negative free-stream pressure gradient. The transition is investigated using the three-parameter turbulence model developed by the authors. The calculation results are compared with the available experimental data. 相似文献
13.
Hairpin-like vortical structures that form in the wall region of turbulent channel flow are investigated. The analysis is
performed by following a procedure in which the Navier-Stokes equations are first integrated by means of a computational code
based on a mixed spectral-finite difference technique in the case of the flow in a plane channel. A DNS turbulent-flow database,
representing the turbulent statistically steady state of the velocity field through 10 viscous time units, is computed and
the vortex-detection method of the imaginary part of the complex eigenvalue pair of the velocity-gradient tensor is applied to the velocity field. As a result, hairpin-like vortical structures are educed. Flow visualizations are provided
of the processes of evolution that characterize hairpin vortices in the wall region of turbulent channel flow. The relationship
is investigated between vortex dynamics and 2nd- and 4th- quadrant events, showing that ejections and sweeps play a fundamental
role in the way the morphological evolution of a hairpin vortex develops with time. 相似文献
14.
D. S. Lokhov A. V. Boiko D. S. Sboev 《Journal of Applied Mechanics and Technical Physics》2005,46(4):496-502
This paper reports results of experiments on controlling longitudinal structures in the boundary layer on a at plate. The longitudinal structures were generated by a controlled vortical disturbance of the external flow by means of a distributed susceptibility mechanism. It is shown that riblets reduce the intensity of both stationary and traveling disturbances. The linear and weakly linear stages in the development of disturbances in the boundary layer are the most favorable for the use of riblets.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 4, pp. 47–54, July–August, 2005. 相似文献
15.
The purpose of the present work is to study the various specific time scales of the turbulent separating flow around a square cylinder, in order to determine the Reynolds number effect on the separating shear layer, where occurs a transition to turbulence. Unsteady analysis based on large eddy simulation (LES) at intermediate Reynolds numbers and laser doppler velocimetry (LDV) measurements at high Reynolds numbers are carried out. The Reynolds number, based on the cylinder diameter D and the inflow velocity U o , is ranging from Re?=?50 to Re?=?300,000. A special focus is performed on the coherent structures developing on the sides and in the wake of a square cylinder. For a large Reynolds number range above Re?≈?1,000, both signatures of Von Karman (VK) and Kelvin–Helmholtz (KH) type vortical structures are found on velocity time samples. The combination of their frequency signature is studied based on Fourier and wavelet analysis. In the present study, We observe the occurrence of KH pairings in the separating shear layer on the side of the cylinder, and confirm the intermittency nature of such a shear flow. These issues concerning the structure of the near wake shear layer which were addressed for the round cylinder case in a recent experimental publication (Rajagopalan and Antonia, Exp Fluids 38:393–402, 2005) are of interest in the present flow configuration as well. 相似文献
16.
A. P. Brylyakov G. M. Zharkova B. Yu. Zanin V. N. Kovrizhina D. S. Sboev 《Journal of Applied Mechanics and Technical Physics》2003,44(5):648-653
Results for a turbulized flow past the windward side of a swept wing model are presented. Origination of steady disturbances in the form of streamwise structures is found. The greatest effect on the formation of these disturbances is exerted by the curvature of the external flow streamlines. The secondary flow in the boundary layer leads to an increase in the characteristic scale of disturbances in the transverse direction, as compared to the flow around the model at a zero yaw angle. 相似文献
17.
A. A. Gurchenkov 《Journal of Applied Mechanics and Technical Physics》2001,42(4):603-606
The paper considers the unsteady flow of a viscous incompressible fluid inside an infinitely long slot with uniform injection or suction of the fluid through the porous walls of the slot. The plates with the fluid are rotated rigidly with constant angular velocity. The unsteady flow is induced by nontorsional vibrations of the upper plate. The flowvelocity field and the tangential stress vectors exerted by the fluid on the upper and lower walls of the slot are determined. In this case, one can find an exact solution of the threedimensional nonstationary Navier–Stokes equations. No restrictions are imposed on the motion pattern of the plate. 相似文献
18.
A mathematical model of turbulent transport processes is modified to make allowance for the turbulent energy gradient and the presence of walls. The modification consists in making the variance tensor in the Gaussian probability density distribution for the initial mole velocities anisotropic for nonzero turbulent energy gradient and a ratio of the turbulence scale to the distance from the wall of the order of unity. Formulas for the variance tensor components are derived and the empirical coefficients of these formulas are determined. The expression for the dimensionless turbulent friction stress is compared with experimental data for three boundary-layer-type flows, namely, in the wake of a cylinder, in the boundary layer on a flat plate, and in a channel with parallel walls. 相似文献
19.
N. I. Lobov 《Fluid Dynamics》2005,40(2):179-182
The effect of longitudinal forced fluid motion on the mechanisms of instability of a convection flow developing in a plane vertical layer in the presence of internal heat sources is considered. It is found that forced motion which intensifies the central stream of the convection flow can lead to moderate stabilization of the hydrodynamic and thermal crisis mechanisms. In the presence of counterstream forced motion the flow stability increases sharply.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 14–17.Original Russian Text Copyright © 2005 by Lobov. 相似文献
20.
A. N. Prokunin 《Fluid Dynamics》2003,38(3):443-457
The results of an experimental investigation of spherical particles with different surface roughnesses rolling under their own weight down an inclined pipe wall in a Newtonian fluid at low Reynolds numbers, both with (friction should be taken into account) and without contact with the wall, are presented. It is shown that a fixed particle moves differently in different fluids with similar viscosities and densities. This fact, as well as the possibility of particle motion without contact with the wall, cannot be explained within the framework of the usual hydrodynamic theories. An example is the dependence of the particle motion on the static pressure. 相似文献