On laminar-turbulent transition in nanofluid flows

The paper presents experimental data on the laminar-turbulent transition in the nanofluid flow in the pipe. The transition in the flows of such fluids is shown to have lower Reynolds numbers than in the base fluid. The degree of the flow destabilization increases with an increase in concentration of nanoparticles and a decrease in their size. On the other hand, in the turbulent flow regime, the presence of particles in the flow leads to the suppression of smallscale turbulent fluctuations. The correlation of the measured viscosity coefficient of considered nanofluids is presented.     

Inherent mechanism of breakdown in laminar-turbulent transition of plane channel flows

We will first list some known facts of transition and turbulence, and then analyze results from direct numerical simulations done for the transition of plane channel flows, thus revealing the key mechanism of breakdown. 1 Arguments based on known facts A superficial reason for the fact that the change of mean flow profile plays the key role in transition is that the mean flow profiles for laminar and turbulent flow are drasti- cally different. But this does not provide the inherent mechanism o…     

Hysteresis of laminar-turbulent transition in a pipe with a divergent inlet section

Gas flow behavior near the laminar-turbulent transition condition in a pipe with a divergent inlet section has been studied experimentally. Hysteresis in the laminar-turbulent transition regime is observed. Also, we have observed unstable, regular vacillation of the flow rate when the time-averaged flow is controlled at the laminar-turbulent critical point with stationary background conditions. The text was submitted by the authors in English.     

Method laminar-turbulent transition control of supersonic boundary layer on a swept wing

A passive control method for supersonic boundary-layer transition on a swept wing using longitudinal roughness is proposed. Tests were carried out to examine the effect of distributed roughness on the development of flow peturbations and on the laminar-turbulent transition. The method makes it possible to manipulate the transition in a wide range, bringing it either closer to the leading edge of the wing by 30 % or delaying it by 40%. This work was supported by the Russian Foundation for Basic Research (Grant No. 05-01-00176).     

Numerical simulation of the laminar-turbulent transition in the flow over a backward-facing step

The capabilities of the quasi-gasdynamic equations as applied to the simulation of laminar-turbulent transitions are demonstrated by computing the viscous compressible gas flow in a channel with an abrupt expansion.     

Influence of blunt-cone tip temperature on the laminar-turbulent transition in hypersonic boundary layers

In the present paper, we report on the results of a combined experimetal and numerical study of the laminar-turbulent transition at Mach number 5.95 in the boundary layers of 7-deg cones with a small nose-tip bluntness radius (down to 1.5 mm). The tip temperature of the model was varied in the range from 90 to 440 K. It was confirmed that the small nose-tip bluntness substantially shifts the position of the transition in downstream direction. This effect was also retained in testing the models with local heating/cooling of the cone tip. It is shown that for the experimental conditions implemented in the Transit-M wind tunnel, ITAM SB RAS, the local heating of blunt cone tips exerts almost no influence on the position of the transition. The local cooling of the cone tip with R = 1.5 mm leads to a shift of the transition position in upstream direction.     

Effect of the surface roughness of blunt cone forebody on the position of laminar-turbulent transition

In the present paper, data on the effect of the surface roughness of blunt cone forebody on the position of laminar-turbulent transition are reported. The study was carried out under freestream Mach 5.95. It was found that the roughness position plays a substantial role in the transition process. Critical Reynolds numbers at which the laminar-turbulent transition occurs on the nose-tip of the model were identified. For the first time, hysteresis in transition position was observed.     

Structure of the channel flow behind a surface-mounted rib under conditions of laminar-turbulent transition

The PIV technique was used to measure the instantaneous vector fields of flow velocity and vorticity behind a thin cross-flow rib installed in a channel with laminar, transient, or turbulent flow. The data were treated statistically to determine the fields of mean longitudinal flow velocity and the correlations of pulsating velocity components 〈u′ν′〉 and 〈u′u′〉. Some features of the flow structure developing under conditions of laminar-turbulent transition behind the rib have been revealed.     

Symmetry-based structure entropy of complex networks

Precisely quantifying the heterogeneity or disorder of network systems is important and desired in studies of behaviors and functions of network systems. Although various degree-based entropies have been available to measure the heterogeneity of real networks, heterogeneity implicated in the structures of networks can not be precisely quantified yet. Hence, we propose a new structure entropy based on automorphism partition. Analysis of extreme cases shows that entropy based on automorphism partition can quantify the structural heterogeneity of networks more precisely than degree-based entropies. We also summarized symmetry and heterogeneity statistics of many real networks, finding that real networks are more heterogeneous in the view of automorphism partition than what have been depicted under the measurement of degree-based entropies; and that structural heterogeneity is strongly negatively correlated to symmetry of real networks.     

On the determination of the position of laminar-turbulent transition in boundary layer by optical methods

As a rule, aerodynamic studies at hypersonic flow velocities are carried out in short-duration wind-tunnel facilities. For such facilities, optical diagnostic methods are most preferable. In the present study, we give for the first time a comparison of two methods for determining the end of laminar-turbulent transition: from the distribution of heat fluxes and from schlieren visualization data for the boundary-layer flow. Parametric data on the position of the transition are obtained. These data can be used in the future as reference ones while calibrating semi-empirical calculation models for the transition.     

Fisher information description of the classical-quantal transition

We investigate the classical limit of the dynamics of a semiclassical system that represents the interaction between matter and a given field. The concept of Fisher Information measure (F) on using as a quantifier of the process, we find that it adequately describes the transition, detecting the most salient details of the changeover. Used in conjunction with other possible information quantifiers, such as the Normalized Shannon Entropy (H) and the Statistical Complexity (C) by recourse to appropriate planar representations like the Fisher Entropy (F×H) and Fisher Complexity (F×C) planes, one obtains a better visualization of the transition than that provided by just one quantifier by itself. In the evaluation of these Information Theory quantifiers, we used the Bandt and Pompe methodology for the obtention of the corresponding probability distribution.     

Functional renormalization description of the roughening transition

We reconsider the problem of the static thermal roughening of an elastic manifold at the critical dimension d=2 in a periodic potential, using a perturbative Functional Renormalization Group approach. Our aim is to describe the effective potential seen by the manifold below the roughening temperature on large length scales. We obtain analytically a flow equation for the potential and surface tension of the manifold, valid for low temperatures. On a length scale L, the renormalized potential is made up of a succession of quasi parabolic wells, matching onto one another in a singular region of width for large L. For strong periodic potential, the perturbation theory breaks down, and we argue, based on a variational calculation, that the transition becomes first order. We also obtain numerically the step energy as a function of temperature, and relate our results to the existing experimental data on ⁴He. Finally, we examine the case of a non local elasticity which is realized physically for the contact line. Received 16 April 1999 and Received in final form 11 October 1999     

Fluid dynamical description of the chiral transition

We investigate the dynamics of the chiral transition in an expanding quark-antiquark plasma. The calculations are made within a linear σ-model with explicit quark and antiquark degrees of freedom. We solve numerically the classical equations of motion for chiral fields coupled to the fluid dynamical equations for the plasma. Fast initial growth and strong oscillations of the chiral field and strong amplification of long wavelength modes of the pion field are observed in the course of the chiral transition.     

The mechanism of breakdown in laminar-turbulent transition of a supersonic boundary layer on a flat plate-temporal mode

Recently, more and more attentions have been paid to the transition and turbulence of compressible flows, especially supersonic flows, but progress is very slow. In general, attentions were paid to the evolution of disturbances in laminar flow region, and the mechanism of breakdown process in laminar-turbulent transition remains unclear. The conventional idea of what leads to laminar-turbulent transition is that the transi-tion starts from the amplification of disturbances, and when the distur…     

Effect of unit Reynolds number on the laminar-turbulent transition on a swept wing in supersonic flow

An experimental study of the influence of unit Reynolds number on the position of laminar-turbulent transition in swept-wing boundary layer at supersonic flow velocities was carried out. In the experiments, a swept-wing model with 3-% circular arc airfoil and 45-deg gliding angle of wing edges was used. The position of the transition was iden-tified using a hot-wire anemometer. It was found that at М = 2 and 2.5, an increase in the unit Reynolds number (Re₁) leads to a transition delay. It was shown that an increase in freestream Mach number and in the level of flow pulsations in the wind-tunnel test section leads to a less pronounced influence of Re1 on the transition position. At a high noise level due to the growth of Mach number or due to the introduction of vortical disturbances, no effect due to unit Reyn-olds number on the transition position was observed.     

Hydrodynamical description of a hadron-quark first-order phase transition

Solutions of hydrodynamical equations are presented for the equation of state of the Van der Waals type allowing for a first-order phase transition. As an example we consider the hadron-quark phase transition in heavy-ion collisions. It is shown that fluctuations dissolve and grow as if the fluid is effectively very viscous. In the vicinity of the critical point even in spinodal region seeds are growing slowly due to viscosity, surface tension and critical slowing down. These non-equilibrium effects prevent enhancement of fluctuations in the near-critical region, which in thermodynamical approach is frequently considered as a signal of the critical endpoint in heavy-ion collisions.