Development of a local disturbance in the boundary layer on a curved surface

The process of nonlinear development of a local transverse disturbance on a concave surface is analyzed and the mechanism of formation of the resulting periodic structure is examined. Attention is concentrated on a qualitative analysis of the flow. Equations describing the development of a transverse disturbance in a laminar boundary layer are obtained on the basis of the asymptotic behavior of the Navier-Stokes equations as Re . A solution describing the Taylor vortices formed between two coaxial cylinders when the inner cylinder rotates is obtained. The experimental data on Görtler vortices in boundary layers are analyzed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 23–31, January–February, 1990.     

Regularization modeling for LES of separated boundary layer flow

Regularization models for the turbulent stress tensor are applied to mixing and separated boundary layers. The Leray and the NS-α models in large-eddy simulation (LES) are compared to direct numerical simulation (DNS) and (dynamic) eddy-viscosity models. These regularization models are at least as accurate as the dynamic eddy-viscosity model, and can be derived from an underlying dynamic principle. This allows one to maintain central transport properties of the Navier-Stokes equations in the model and to extend systematically toward complex applications. The NS-α model accurately represents the small-scale variability, albeit at considerable resolution. The Leray model was found to be much more robust, allowing simulations at high Reynolds number. Leray simulations of a separated boundary layer are shown for the first time. The strongly localized transition to turbulence that arises under a blowing and suction region over a flat plate was captured accurately, quite comparable to the dynamic model. In contrast, results obtained with the Smagorinsky model, either with or without Van Driest damping, yield considerable errors, due to its excessive dissipation.     

Effect of local forcing on a turbulent boundary layer

An experimental study is performed to analyze flow structures behind local suction and blowing in a flat-plate turbulent boundary layer. The local forcing is given to the boundary layer flow by means of a sinusoidally oscillating jet issuing from a thin spanwise slot at the wall. The Reynolds number based on the momentum thickness is about Re _θ =1700. The effects of local forcing are scrutinized by altering the forcing frequency (0.011 ≤ f ⁺≤ 0.044). The forcing amplitude is fixed at A ₀=0.4. It is found that a small local forcing reduces the skin friction and the skin friction reduction increases with the forcing frequency. A phase-averaging technique is employed to capture the large-scale vortex evolution. An organized spanwise vortical structure is generated by the local forcing. The cross-sectional area of vortex and the time fraction of vortex are examined by changing the forcing frequency. An investigation of the random fluctuation components reveals that turbulent energy is concentrated near the center of vortical structures. Received: 17 March 2000/Accepted: 3 April 2001     

Design of a wing airfoil in a flow with a separated turbulent boundary layer

The problem of designing the contour of an airfoil in a viscous (incompressible and compressible) flow with a separated turbulent boundary layer from a pressure distribution given on the separationless part of the contour is solved using the boundary layer theory together with the separated flow model proposed in [1]. Numerical calculations are carried out to demonstrate the possibilities of the method.Kazan'. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.3, pp. 83–91, May–June, 1994.     

Effect of periodic action on boundary layer stability

The effect of a wave traveling over the surface and suction-blowing in the form of a traveling wave on boundary layer stability and laminarturbulent transition is investigated. The perturbation parameters are assumed not to be related to the parameters of the Tollmien-Schlichting wave. The parameters corresponding to an increase in the critical Reynolds number by a factor of 2–2.5 are determined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 109–115, May–June, 1988.The author is grateful to V. A. Kuparev for supplying the program for calculating the stability of the boundary layer.     

Research on the flow stability in a cylindrical particle two-phase boundary layer

IntroductionThecylindricalparticletwo_phaseflowsareofparticularinterestintheprocessingofcompositematerials ,textileindustry ,papermaking ,chemicalengineering ,foodprocessing[1].Thecylindricalparticlesinaflowcanmakethereinforcementofmaterials,thechangeofphysicalpropertyformaterialsandthereductionofdrag .Arranaga[2 ]reportedthatdragreductioneffectsareupto 60 %inpipeflowsbyaddingcylindricalparticlestoflow .Thecylindricalparticleshavealsoeffectsonthemechanismsofflowstability .Theeffectofcylindric…     

Effect of the disturbance frequency and the boundary layer thickness on heat transfer in a flow over a cubic cavity

The results of the numerical modeling of heat transfer in flows over cubic cavities are presented. The effect of different parameters of the incident laminar flow, such as the disturbance frequency, the boundary layer thickness, and the main flow velocity, on the flow stability is investigated. It is shown that the integral heat flux considerably depends on the disturbance frequencies in the oncoming flow, the frequencies leading to heat transfer intensification being determined by the stability of the mixing layer between the cavity and the main flow. The calculated integral heat-transfer parameters are compared with experimental data. The calculated Reynolds-number dependence of the Nusselt number is found to be in good agreement with experiment.     

Effect of a steady periodic velocity inhomogeneity on boundary layer stability

Direct numerical simulation is used to investigate laminar-turbulent transition in a boundary layer with a span-periodic inhomogeneity of the velocity profile which is created artificially. It is shown that the presence of the inhomogeneity leads to a slowing down of the growth of unstable perturbations and a delaying of the laminar-turbulent transition.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 45–52, July–August, 1995.     

Disturbed boundary layer flow with local time-dependent surface heating

Local flows in a laminar boundary layer flowing over surface heating elements are investigated. Mathematical models of disturbed flows are constructed on the basis of an asymptotic analysis and the similarity parameters are determined. The time-dependent local heating regimes ensuring control of separation and flow stability in the boundary layer are studied. The results of a numerical and analytic analysis are obtained.     

Effect of spanwise-varying local forcing on turbulent separated flow over a backward-facing step

An experimental study was made of turbulent separated flows over a backward-facing step. A local forcing was given to the separated flow by means of a sinusoidally oscillating jet issuing from a thin slit near the separation line. To produce a spanwise-varying local forcing at the separation edge, a banded thin tape covered the slit. Effects of the spanwise-varying local forcings on the separated flow were scrutinized by altering the spatially banded blocking width (w) and the open slit distance (g). An optimal value of w/g was sought, which led to the minimum reattachment length (x _R ). The effect of spanwise-varying local forcing on x _R was found to be slight compared to the case of two-dimensional forcing (w=0). The experiment was made at Re _H =33000 and A ₀=0.018 by changing the forcing frequency (0?St _H ?1.0).     

Effect of system rotating on turbulent boundary layer flow

This paper experimentally investigated the effect of rotating on the turbulent boundary layer flow using hot-wire. The experiments were completed in a rotating rig with a vertical axis and four measured positions along the streamwise direction in channel, which focuses on the flow flied in the rotating channel. The rotating effects on velocity profile, wall shear stress and semi-logarithmic mean velocity profile are discussed in this paper. The results indicated that: due to the Coriolis force induced by rotating, the phenomenon of velocity deficit happens near the leading side. The velocity deficit near the leading side, do not increase monotonically with the increase of Ro. The trend of the velocity deficit near the leading side is also affected by the normal component of pressure gradient, which is another important force in the cross-section of the rotating channel. The wall shear stress near the trailing side is larger than that on the leading side, and the semi-logarithmic mean velocity profile is also different under rotating effects. The phenomenon reveals that the effect of rotation penetrates into the logarithm region, and the flow near the leading side tends to turn into laminar under the effect of rotation. The rotation correction of logarithmic law is performed in current work, which can be used in the wall function of CFD to increase the simulating accuracy at rotating conditions.     

The influence of the periodic disturbance on the local heat transfer in separated and reattached flow

A numerical study based on the large eddy simulation methodology was made of heat transfer in locally disturbed turbulent separated and reattached flow over a backward facing step. The local disturbance was given to the flow by a sinusoidally blowing/suction of the fluid into a separated shear layer. The Reynolds number was fixed at 33,000 and Richardson number at 0.5. The disturbance frequency was varied in the range 0 ≤ St ≤ 2, where St is the Strouhal number of disturbance. The obtained results revealed the existence of an optimum perturbation frequency value, St = 0.25, in terms of the reduced reattachment length. At this frequency the heat transfer is significantly enhanced in the recirculation zone. The influence of the frequency and the amplitude of disturbance, in the maximum heat transfer positions and the maximum local Nusselt number, is analysed.     

Open and closed-loop experiments to identify the separated flow dynamics of a thick turbulent boundary layer

Open and closed-loop flow control experiments were performed on the transient attachment and separation mechanisms of a thick turbulent boundary layer (TBL). Without actuation, the TBL is subjected to an adverse pressure gradient and separates downstream of a sharp variation in the wall geometry. Departing from a given geometry and steady operations of vortex generator actuators, the control objective was to attach the flow in the separated region with a minimum of injected fluid using adaptation of the closed-loop control. The large scale of the facility (i.e., δ = 20 cm upstream of separation) induces large time scales and large Reynolds numbers of the flow to be controlled. It is found to consequently induce large time scales of the separation/attachment mechanisms, making the dynamic closed-loop implementation easier. Open-loop tests were first performed to extract the adequate input/output variables for closed-loop implementations. The chosen input variable was the Duty Cycle, DC, which enables sending of a control action at least 10 times faster than the time scales of the attachment/separation process. The chosen output variable was the voltage signal from a hot-film probe located on the flap which characterizes the degree of separation. In open loop, both the large scale (i.e., large time scales) of the present facility (Carlier and Stanislas in J Fluid Mech 535(36):143–188, 2005) and the well-defined excitation (Braud and Dyment in Phys Fluids 24:047102, 2012) help to extract the different time scales involved and to identify the whole system (actuators, baseline flow and sensor). Three Reynolds numbers based on the momentum thickness of the boundary layer near the actuators and upstream of separation were investigated (Re _θ  = 7,500, 10,500 and 12,600) through variation of the free-stream velocity (U _∞ = 5, 8, 10 m/s). These three systems were found to behave like first-order linear systems, with coefficients that need to be adapted depending on the Reynolds number. From Re _θ  = 7,500 to Re _θ  = 12, 600, the time scale and static gain of the linear system needed to be almost doubled. A simple controller (Proportional-Integral) was implemented in closed-loop configuration, improving the reactivity of the system. Robustness was tested by varying the free-stream velocity. Closed-loop control based on a fixed reference was unsuccessful as it failed to account for the effect of the Reynolds number. This was successfully overcome by tracking a given state of the flow using a simple P controller to adapt the reference according to variations of Re. The P controller, acting on the DC variable, compensates the corresponding variations of VR (ratio between the free-stream and the jet exit velocity).     

Numerical simulation of stabilization of the boundary layer on a surface with a porous coating in a supersonic separated flow

Stability of a supersonic (M _∞ = 5.373) boundary layer with local separation in a compression corner with a passive porous coating partly absorbing flow perturbations is considered by solving two-dimensional Navier-Stokes equations numerically. The second mode of disturbances of a supersonic boundary layer is demonstrated to be the most important one behind the boundary-layer reattachment point. The possibility of effective stabilization of these disturbances behind the reattachment point with the use of porous coatings is confirmed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 39–47, March–April, 2007.     

Effect of local heat supply to a turbulent boundary layer on the friction

The results of calculating a supersonic turbulent boundary layer on a flat plate in the presence of thermal energy supply to the boundary layer are presented. Two methods of energy supply are considered: heating a local interval of the surface, which is otherwise thermally insulated and using a local volume heat source. It is shown that for the same amount of heat supplied to the gas volume heating leads, under certain conditions, to greater friction reduction than the surface heating. Localization of the energy supply zone leads to the intensification of the viscous drag reduction effect and to a greater decrease in the local friction coefficient, which extends a considerable distance downstream. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 48–56, January–February, 1997. The work was carried out with financial support from the Russian Foundation for Fundamental Research (project No. 93-013-17600).     

Stability of a compressible boundary layer relative to a localized disturbance

The problem of stability of an incompressible boundary layer relative to a localized disturbance is considered in a linear approximation. It is shown that the stability analysis reduces to the study of a discrete spectrum of eigenvalues of the corresponding boundary value problem. By means of numerical integration, analysis of the character of the emerging instability is carried out for an unstable mode for the Mach number M = 4.5.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, pp. 107–114, May–June, 1973.The author is grateful to V. V. Struminskii for his interest in this work; he is grateful to L. B. Aizin for useful discussion of the subjects broached, and to A. A. Maslov for the great help in carrying out the numerical calculations.     

Effect of sound on boundary layer stability at high Reynolds numbers

Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 178–180, January–February, 1991.     

Effect of electrohydrodynamic interaction on the stability of a flat plate laminar boundary layer

The stability of a unipolarly charged electrohydrodynamic boundary layer on a flat dielectric plate along which an electric current flows between electrodes located on the plate is investigated within the framework of the linear theory. The solution of the steady-state problem is obtained on the basis of methods developed earlier for conditions typical of aerodynamical experiments and various electric currents and electrode voltages. The effect of the interaction between perturbations of the electric and hydrodynamic flow parameters on the flow stability is estimated within the framework of the locally homogeneous approximation. This effect turns out to be insignificant under the conditions considered. It is shown that steady-state electrohydrodynamic action on the main flow makes it possible to obtain “accelerating” velocity profiles with increased absolute values of the second derivative in the transverse direction. This ensures a significant increase in the critical Reynolds numbers of loss of stability and a narrowing of the growing perturbation wavenumber range.