Publications
60 results found
RUBAN AI, TURKYILMAZ I, 2000, On laminar separation at a corner point in transonic flow, Journal of Fluid Mechanics, Vol: 423, Pages: 345-380, ISSN: 0022-1120
<jats:p>The separation of the laminar boundary layer from a convex corner on a rigid body contour in transonic flow is studied based on the asymptotic analysis of the Navier–Stokes equations at large values of the Reynolds number. It is shown that the flow in a small vicinity of the separation point is governed, as usual, by strong interaction between the boundary layer and the inviscid part of the flow. Outside the interaction region the Kármán–Guderley equation describing transonic inviscid flow admits a self-similar solution with the pressure on the body surface being proportional to the cubic root of the distance from the separation point. Analysis of the boundary layer driven by this pressure shows that as the interaction region is approached the boundary layer splits into two parts: the near-wall viscous sublayer and the main body of the boundary layer where the flow is locally inviscid. It is interesting that contrary to what happens in subsonic and supersonic flows, the displacement effect of the boundary layer is primarily due to the inviscid part. The contribution of the viscous sublayer proves to be negligible to the leading order. Consequently, the flow in the interaction region is governed by the <jats:italic>inviscid</jats:italic>–<jats:italic>inviscid interaction</jats:italic>. To describe this flow one needs to solve the Kármán–Guderley equation for the potential flow region outside the boundary layer; the solution in the main part of the boundary layer was found in an analytical form, thanks to which the interaction between the boundary layer and external flow can be expressed via the corresponding boundary condition for the Kármán–Guderley equation. Formulation of the interaction problem involves one similarity parameter which in essence is the Kármán–Guderley parameter suitably modified for the flow at hand. The solution of the
Buldakov EV, Chernyshenko SI, Ruban AI, 2000, On the uniqueness of steady flow past a rotating cylinder with suction, Journal of Fluid Mechanics, Vol: 411, Pages: 213-232, ISSN: 0022-1120
Türkyılmazoglu M, Gajjar JSB, Ruban AI, 1999, The Absolute Instability of Thin Wakes in an Incompressible/Compressible Fluid, Theoretical and Computational Fluid Dynamics, Vol: 13, Pages: 91-114, ISSN: 0935-4964
VV Sychev, AI Ruban, VicVSychev, et al., 1998, Asymptotic Theory of Separated Flows, Publisher: Cambridge University Press
Tsao J-C, Rothmayer AP, Ruban AI, 1997, Stability of air flow past thin liquid films on airfoils, Computers & Fluids, Vol: 26, Pages: 427-452, ISSN: 0045-7930
He J, Kazakia JY, Ruban AI, et al., 1996, A model for adiabatic supersonic turbulent boundary layers, Theoretical and Computational Fluid Dynamics, Vol: 8, Pages: 349-364, ISSN: 0935-4964
Cassel KW, Ruban AI, Walker JDA, 1996, The influence of wall cooling on hypersonic boundary-layer separation and stability, Journal of Fluid Mechanics, Vol: 321, Pages: 189-216, ISSN: 0022-1120
<jats:p>The effect of wall cooling on hypersonic boundary-layer separation near a compression ramp is considered. Two cases are identified corresponding to the value of the average Mach number <jats:inline-formula id="frm1">$\overline{M}$</jats:inline-formula> across the upstream boundary layer approaching the compression ramp. The flow is referred to as supercritical for <jats:inline-formula id="frm2">$\overline > 1$</jats:inline-formula> and subcritical for <jats:inline-formula id="frm3">$\overline{M} < 1$</jats:inline-formula>. The interaction is described by triple-deck theory, and numerical results are given for both cases for various ramp angles and levels of wall cooling. The effect of wall cooling on the absolute instability described recently by Cassel, Ruban & Walker (1995) for an uncooled wall is of particular interest; a stabilizing effect is observed for supercritical boundary layers, but a strong destabilizing influence occurs in the subcritical case. Wall cooling also influences the location and size of the separated region. For supercritical flow, progressive wall cooling reduces the size of the recirculating-flow region, the separation point moves downstream, and upstream influence is diminished. In contrast for the subcritical case downstream influence is reduced with increased cooling. In either situation, a sufficient level of wall cooling eliminates separation altogether for the ramp angles considered. The present numerical results closely confirm the strong wall cooling theory of Kerimbekov, Ruban & Walker (1994).</jats:p>
Duck PW, Ruban AI, Zhikharev CN, 1996, The generation of Tollmien-Schlichting waves by free-stream turbulence, Journal of Fluid Mechanics, Vol: 312, Pages: 341-371, ISSN: 0022-1120
<jats:p>The phenomenon of Tollmien-Schlichting wave generation in a boundary layer by free-stream turbulence is analysed theoretically by means of asymptotic solution of the Navier-Stokes equations at large Reynolds numbers (<jats:italic>Re</jats:italic> → ∞). For simplicity the basic flow is taken to be the Blasius boundary layer over a flat plate. Free-stream turbulence is taken to be uniform and thus may be represented by a superposition of vorticity waves. Interaction of these waves with the flat plate is investigated first. It is shown that apart from the conventional viscous boundary layer of thickness <jats:italic>O</jats:italic>(<jats:italic>Re</jats:italic><jats:sup>−1/2</jats:sup>), a ‘vorticity deformation layer’ of thickness <jats:italic>O</jats:italic>(<jats:italic>Re</jats:italic><jats:sup>−1/4</jats:sup>) forms along the flat-plate surface. Equations to describe the vorticity deformation process are derived, based on multiscale asymptotic techniques, and solved numerically. As a result it is shown that a strong singularity (in the form of a shock-like distribution in the wall vorticity) forms in the flow at some distance downstream of the leading edge, on the surface of the flat plate. This is likely to provoke abrupt transition in the boundary layer. With decreasing amplitude of free-stream turbulence perturbations, the singular point moves far away from the leading edge of the flat plate, and any roughness on the surface may cause Tollmien-Schlichting wave generation in the boundary layer. The theory describing the generation process is constructed on the basis of the ‘triple-deck’ concept of the boundary-layer interaction with the external inviscid flow. As a result, an explicit formula for the amplitude of Tollmien-Schlichting waves is obtained.</jats:p>
Cassel KW, Ruban AI, Walker JDA, 1995, An instability in supersonic boundary-layer flow over a compression ramp, Journal of Fluid Mechanics, Vol: 300, Pages: 265-285, ISSN: 0022-1120
<jats:p>Separation of a supersonic boundary layer (or equivalently a hypersonic boundary layer in a region of weak global interaction) near a compression ramp is considered for moderate wall temperatures. For small ramp angles, the flow in the vicinity of the ramp is described by the classical supersonic triple-deck structure governing a local viscous-inviscid interaction. The boundary layer is known to exhibit recirculating flow near the corner once the ramp angle exceeds a certain critical value. Here it is shown that above a second and larger critical ramp angle, the boundary-layer flow develops an instability. The instability appears to be associated with the occurrence of inflection points in the streamwise velocity profiles within the recirculation region and develops as a wave packet which remains stationary near the corner and grows in amplitude with time.</jats:p>
Kerimbekov RM, Ruban AI, Walker JDA, 1994, Hypersonic boundary-layer separation on a cold wall, Journal of Fluid Mechanics, Vol: 274, Pages: 163-195, ISSN: 0022-1120
<jats:p>An asymptotic theory of laminar hypersonic boundary-layer separation for large Reynolds number is described for situations when the surface temperature is small compared with the stagnation temperature of the inviscid external gas flow. The interactive boundary-layer structure near separation is described by well-known tripledeck concepts but, in contrast to the usual situation, the displacement thickness associated with the viscous sublayer is too small to influence the external pressure distribution (to leading order) for sufficiently small wall temperature. The present interaction takes place between the main part of the boundary layer and the external flow and may be described as inviscid–inviscid. The flow in the viscous sublayer is governed by the classical boundary-layer equations and the solution develops a singularity at the separation point. A main objective of this study is to show how the singularity may be removed in different circumstances.</jats:p>
Ruban A, 1994, Numerical methods in the theory of boundary-layer interaction with inviscid flow, TsAGI Journal
Ruban AI, 1990, Propagation of wave packets in the boundary layer on a curved surface, Fluid Dynamics, Vol: 25, Pages: 213-221, ISSN: 0015-4628
Rozhko SB, Ruban AI, Timoshin SN, 1988, Interaction of a three-dimensional boundary layer with an extensive obstacle, Fluid Dynamics, Vol: 23, Pages: 30-37, ISSN: 0015-4628
KRAVTSOVA MA, RUBAN AI, 1988, DETACHMENT OF A SUPERSONIC BOUNDARY-LAYER IN FRONT OF THE BOTTOM EDGE OF A CONTOUR OF A BODY, USSR COMPUTATIONAL MATHEMATICS AND MATHEMATICAL PHYSICS, Vol: 28, Pages: 177-184, ISSN: 0041-5553
Rozhko SB, Ruban AI, 1987, Longitudinal-transverse interaction in a three-dimensional boundary layer, Fluid Dynamics, Vol: 22, Pages: 362-371, ISSN: 0015-4628
Ruban AI, Timoshin SN, 1986, Propagation of perturbations in the boundary layer on the walls of a flat channel, Fluid Dynamics, Vol: 21, Pages: 230-235, ISSN: 0015-4628
Kravtsova M, Ruban A, 1985, Nonstationary boundary layer on a rotationally vibrating cylinder in transverse flow, Uch. Zap. TsAGI
Ruban AI, 1985, On the generation of Tollmien-Schlichting waves by sound, Fluid Dynamics, Vol: 19, Pages: 709-717, ISSN: 0015-4628
Ruban A, 1984, On Tollmien-Schlichting Wave Generation by Sound, Laminar-Turbulent Transition
Ruban AI, 1984, Nonlinear equation for amplitude of Tollmien-Schlichting waves in a boundary layer, Fluid Dynamics, Vol: 18, Pages: 882-889, ISSN: 0015-4628
Ruban AI, 1982, Stability of preseparation boundary layer on the leading edge of a thin airfoil, Fluid Dynamics, Vol: 17, Pages: 860-867, ISSN: 0015-4628
Ruban AI, 1982, Asymptotic theory of short separation regions on the leading edge of a slender airfoil, Fluid Dynamics, Vol: 17, Pages: 33-41, ISSN: 0015-4628
Ruban AI, 1982, Singular solution of boundary layer equations which can be extended continuously through the point of zero surface friction, Fluid Dynamics, Vol: 16, Pages: 835-843, ISSN: 0015-4628
Ruban AI, 1981, Asymptotic theory of flow attachment for a viscous incompressible fluid, Fluid Dynamics, Vol: 15, Pages: 844-851, ISSN: 0015-4628
Ruban AI, 1978, Numerical solution of the local asymptotic problem of the unsteady separation of a laminar boundary layer in a supersonic flow, USSR Computational Mathematics and Mathematical Physics, Vol: 18, Pages: 175-187, ISSN: 0041-5553
Ruban A, 1976, On the asymptotic theory of flow near the trailing edge of a thin aerofoil, Uch. Zap. TsAGI
Ruban A, 1976, Numerical method for solving the free-interaction problem, Uch. Zap. TsAGI
Ruban A, 1975, On the theory of laminar flow separation from a corner point on a solid surface, Uch. Zap. TsAGI
Ruban A, 1973, Laminar separation from a corner point of a rigid body contour, Uch. Zap. TsAGI
Ruban A, Sychev VV, 1973, Hypersonic viscous gas flow over small aspect ratio wing, Uch. Zap. TsAGI
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