Alexander Fedorov

• Doctor of Philosophy
• Professor (Associate) at Moscow Institute of Physics and Technology

Within the frameworks of the amplitude method and the linear stability theory, a statistical model of the initial stage of laminar–turbulent transition caused by atmospheric particulates (aerosols) penetrating into the boundary layer is developed. The model accounts for the process of boundary layer receptivity to particulates, asymptotic behaviour...

Under the low-noise Mach 3 flight conditions for a supersonic passenger aircraft having unswept wings with a thin parabolic airfoil, laminar-turbulent transition is due to amplification of the first mode. Stability of a local self-similar boundary layer over such a wing is investigated both using the eN\documentclass[12pt]{minimal} \usepackage{amsm...

In the paper (Theoret Comput Fluid Dyn 36:705–722, 2022), we analyzed acoustic receptivity of the boundary layer on a flat plate in Mach 6 flow at various angles of attack (AoA). It was shown that slow and fast acoustic waves passing through: a bow shock at AoA=-5∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{a...

Theoretical assessments of the crossflow (CF) stabilization due to flow slip produced by small grooves on a swept supersonic wing are performed using the linear theory for inviscid flow, the local similar approximation of the boundary layer flow, the slip boundary conditions on the grooved surface and the linear stability theory. The eN\documentcla...

Direct numerical simulation and theoretical analysis of acoustic receptivity are performed for the boundary layer on a flat plate in Mach 6 flow at various angles of attack (AoA). Slow or fast acoustic wave passes through: a bow shock at AoA =-5∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackag...

Theoretical analysis of attachment-line instabilities is performed for supersonic swept flows using the compressible Hiemenz approximation for the mean flow and the successive approximation procedures for disturbances. The theoretical model captures the dominant attachment-line modes in wide ranges of the sweep Mach number ${M_e}$ and the wall temp...

Mack (1977) criticized methods referring to a single frequency perturbation for correlation of transition prediction because the external disturbance source (like free stream turbulence) should have a broadband spectrum. Delta-correlated perturbations are characterized by the mean square of physical amplitude, which is expressed as a double integra...

Numerical and theoretical stability studies are conducted for a supersonic M = 2.0 flow over a flat plate with a spanwise strip of distributed suction. Propagation of artificially excited 3D wave trains relevant to the first-mode instability are considered. Direct numerical simulations (DNS) as well as assessments based on the linear stability theo...

Atmospherical particles can be the main reason for boundary layer instability, leading to a laminar-turbulent transition on aerodynamically smooth bodies. On the height of about 20-30 km, the concentration of submicron particles is relatively high. Such particles are able to hit leading edges of an aircraft, exciting wave packets of first and/or se...

The presence of the point of maximum amplification on the upswept parabolic wing at Mach 3 has been verified by using direct numerical simulation. Previously, this point was detected using linear stability analysis. The general pattern in the development of instabilities in the boundary layer is confirmed. The maximum amplitude of disturbances in t...

Experiments show that a sudden expansion of supersonic flow may strongly stabilize or even relaminarize the boundary layer. Only few theoretical studies addressed this effect considering evolution of small disturbances in cases of Mach number less than 4, where the first mode is most unstable. This paper addresses stability of a hypersonic (Mach 6)...

Mack (1977) criticized methods referring to a single frequency perturbation for correlation of transition prediction because the external disturbance source (like free stream turbulence) should have a broad band spectrum. Delta-correlated perturbations are characterized by the mean square of physical amplitude, which is expressed as a double integr...

Mack (1977) criticized methods referring to a single frequency perturbation for correlation of transition prediction because the external disturbance source (like free stream turbulence) should have a broad band spectrum. Delta-correlated perturbations are characterized by the mean square of physical amplitude, which is expressed as a double integr...

Prerecorded talk at DFD 2020 virtual meeting

Aerodynamic parameters and stability of a near-wall flow over wavy plates of varying shapes in the free stream of Mach = 6 are investigated by means of numerical simulations. The wavy wall produces a stabilizing effect on a high-speed boundary layer by reducing second-mode instability amplitudes that may eventually delay the laminar-turbulent trans...

The wall normal gas injection effect on the heat transfer and the boundary-layer stability is investigated for the high-speed flow over hemispherical model of space vehicle. The heat flux distributions on the body surface are obtained using numerical solutions of the Navier-Stokes equations for laminar axisymmetric flow. The boundary layer stabilit...

Atmospheric particulates may be a major source of boundary-layer instabilities leading to laminar–turbulent transition on aerodynamically smooth bodies flying at supersonic speeds. Particulates penetrating into the boundary-layer flow can excite wavepackets of the first- and/or second-mode instability. The packets grow downstream, reach the thresho...

The effect of a Mach wave (N wave) on laminar-turbulent transition induced by the first instability mode (Tollmien–Schlichting wave) in the flat-plate boundary layer is investigated on the basis of the numerical solution of Navier–Stokes equations at the freestream Mach number of 2.5. In accordance with the experiment, the N wave is generated by a...

The generation of a turbulent spot by an unstable wave packet propagating in a Mach-6 flat-plate boundary layer is considered. The asymptotic shape of the wave packet is obtained in the far field from the excitation point using linear stability theory. Unsteady boundary conditions are formulated for direct numerical simulation. They allow for excit...

A method for direct numerical simulation of three-dimensional unsteady disturbances leading to a laminar–turbulent transition at hypersonic flow speeds is proposed. The simulation relies on solving the full three-dimensional unsteady Navier–Stokes equations. The computational technique is intended for multiprocessor supercomputers and is based on a...

Receptivity of high-speed boundary layers in calorically perfect gas is considered within the framework of fluctuating hydrodynamics introduced by Landau and Lifshitz (“Hydrodynamic Fluctuations,” Soviet Physics, JETP, Vol. 5, No. 3, 1957, pp. 512–513) for a one-component fluid. It is assumed that kinetic fluctuations manifest themselves in the gov...

The linear stability analysis predicts that the Mack second mode propagating in the boundary layer on a sufficiently cold plate can radiate acoustic waves into the outer inviscid flow. This effect, which is called as a spontaneous radiation (or emission) of sound, is associated with synchronization of the second mode with slow acoustic waves of the...

Direct numerical simulations of a three-dimensional wave packet propagating over a 5.5 deg compression corner at the freestream Mach number 5.373 are carried out. The Navier-Stokes equations are integrated using an implicit finite volume shock-capturing method with the second-order approximation in space and time. After computing the laminar flowfi...

Direct numerical simulations of three-dimensional wave trains propagating over a 5.5 degree compression corner at the freestream Mach number 5.373 are carried out. The undisturbed boundary layer separates upstream of the corner and forms a shallow separation bubble. To generate wave trains unsteady disturbances are imposed onto the basic flow using...

Issues related to prediction of laminar-turbulent transition on hypersonic configurations in high-altitude flight are discussed. The laminar flow control strategy and appropriate laminarization methods for high-speed vehicles are reviewed. The paper is aimed to motivate the transition study groups to integrate their knowledge and tools in the ratio...

A localized heating or cooling effect on stability of the boundary-layer flow on a sharp cone at zero angle of attack and freestream Mach number 6 is analyzed. Experiments were carried out in the Transit-M wind tunnel of the Institute of Theoretical and Applied Mechanics (Novosibirsk, Russia) for different heating/cooling intensities and freestream...

Direct numerical simulations of a three-dimensional wave packet propagating over a 5.5 degree compression corner at the freestream Mach number 5.373 are carried out. The Navier–Stokes equations are integrated using an implicit finite-volume shock-capturing method with the second-order approximation in space and time. After computing the laminar flo...

An error in the complex representation of the porous-coating model used in the study by Fedorov et al . ( J. Fluid Mech. , vol. 479, 2003, pp. 99–124), investigating the stabilization effect of ultrasonically absorptive coatings on hypersonic boundary layers, is pointed out and corrected. This error has been acknowledged by Fedorov et al . ( J. Flu...

Two-dimensional direct numerical simulations and the linear stability analysis are performed for a flat-plate boundary layer in the Mach 6 free stream with the presence of local volume energy supply. It is expected that this technique can be used for the laminar flow control at high speeds where the second mode waves dominate. It is shown that the...

Stability analyses of high-speed boundary-layer flow past a 5° half angle sharp cone with the wall-normal injection of air through a porous strip are performed using Navier-Stokes solutions for the mean flow and linear stability theory. The configuration and free-stream parameters are chosen to be similar to the experiments, which were carried out...

Results of an experimental study of the laminar-turbulent transition in a hypersonic flow around cones with different bluntness radii at a zero angle of attack, free-stream Mach number M∞ = 6, and unit Reynolds number in the interval Re∞,1 = 5.79 · 106–5.66 · 107 m−1 are presented. Flow regimes in which a reverse of the laminar-turbulent transition...

A localized heating or cooling effect on stability and transition of the boundary layer flow on a sharp cone at zero angle of attack and free-stream Mach number 6 is analyzed. Experiments were carried out in the Transit-M wind tunnel of Institute of Theoretical and Applied Mechanics (Novosibirsk, Russia) for different heating/cooling intensities an...

A localized heating or cooling effect on stability and transition of the boundary layer flow on a sharp cone at zero angle of attack and free-stream Mach number 6 is analyzed. Experiments were carried out in the Transit-M wind tunnel of Institute of Theoretical and Applied Mechanics (Novosibirsk, Russia) for different heating/cooling intensities an...

Laminar-turbulent transition in the boundary layer at supersonic speeds can be initiated by small solid particles present in the free stream. Particulates interacting with the boundary-layer flow generate unstable wavepackets related to Tollmien-Schlichting (TS) waves. The latter grow downstream and ultimately break down to turbulent spots. This sc...

Numerical simulations of the linear and nonlinear two-dimensional Navier–Stokes equations, and linear stability theory are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings. The porous coatings consist of a uniform array of rectangular pores (slots) with a range of porosities and pore aspect ratios. F...

Stability of a supersonic near-wall flow over a shallow grooved plate in the freestream of Mach 6 is investigated by means of numerical simulations and wind-tunnel experiments. Numerical solutions of two-dimensional Navier–Stokes equations are used to model propagation of artificial disturbances of several fixed frequencies generated by an actuator...

Two-dimensional direct numerical simulation (DNS) of the receptivity of a flat-plate boundary layer to temperature spottiness in the Mach 6 free stream is carried out. The influence of spottiness parameters on the receptivity process is studied. It is shown that the temperature spots propagating near the upper boundary-layer edge generate mode F in...

A localized heating or cooling effect on stability and transition of the boundary layer flow on a sharp cone at zero angle of attack at the free-stream Mach number 6 is analyzed using the linear stability theory. Three different locations of the heating/cooling strip are considered. The steady-state laminar flow solution is calculated using the axi...

Laminar-turbulent transition in the boundary-layer flow at supersonic speeds can be initiated by small solid particles present in the free stream. Particulates interacting with the boundary layer generate unstable wave-packets related to Tollmien-Schlichting (TS) waves. These wave-packets grow downstream and ultimately break down to turbulent spots...

Ultrasonically absorptive coatings can suppress the second-mode instability in a hypersonic boundary layer, and thereby delay laminar-turbulent transition. Theory and numerical simulations indicate that this stabilization effect essentially depends on the ultrasonically absorptive coating thickness. It is expected that optimal coatings may be sever...

The amplitude method is used for predictions of the roughness-induced transition on a parabolic arc-shaped swept wing in Mach=3.5 free stream. As contrasted to the eN method, the amplitude method incorporates the excitation of stationary CF-vortices by local and/or distributed roughness, downstream amplification of these vortices and the amplitude...

Direct numerical simulation (DNS) of receptivity of a boundary layer over flat plate is carried out. The free stream Mach number is equal to 6. The following two-dimensional disturbances are introduced into the free-stream flow: fast and slow acoustic waves, temperature spottiness. A theoretical model describing the excitation of unstable waves in...

The discrete spectrum of disturbances in high-speed boundary layers is discussed with emphasis on singularities caused by synchronization of the normal modes. Numerical examples illustrate different spectral structures and jumps from one structure to another with small variations of basic flow parameters. It is shown that this singular behavior is...

In this work, two-dimensional direct numerical simulation (DNS) of receptivity and stability of a high- speed boundary layer is carried out. There are three types of free-stream small disturbances: fast and slow acoustic waves, temperature spottiness and vorticity fluctuations. Receptivity to all of these small disturbances is considered in our com...

Laminar-turbulent transition in a high-speed boundary layer can be initiated by small solid particles present in atmosphere. Particulates interacting with the boundary-layer flow can generate unstable wave-packets which ultimately break down to turbulent spots. A theoretical model describing this receptivity mechanism is developed and incorporated...

A two-dimensional direct numerical simulation (DNS) of receptivity of a flat-plate boundary layer to temperature spottiness in Mach 6 free stream is carried out. The influence of spottiness parameters to the receptivity process is studied. It is shown that the temperature spots propagating near the upper boundary-layer edge generate mode F. Further...

This article reviews stability and laminar-turbulent transition in high-speed boundary-layer flows, emphasizing qualitative features of the disturbance spectrum leading to new mechanisms of receptivity and instability. It is shown that the extension of subsonic and low-supersonic stability concepts and transition prediction methods to hypersonic sp...

Ultrasonically absorptive coatings (UAC) can stabilize the Mack second mode and thereby increase the laminar run on configurations where laminar-turbulent transition is second-mode dominated. Theory indicates that the stabilization effect can be essentially enhanced by increasing the UAC porosity. However, direct numerical simulations (DNS) showed...

This report summarizes modeling of surface dielectric barrier discharge (SDBD) and flow control. A physics-based phenomenological model was used for analytical approximations of SDBD-induced body force and heat source, which were incorporated into a Navier-Stokes solver for CFD studies. Results show that a SDBD actuator can strongly affect laminar...

Two-dimensional direct numerical simulation (DNS) of receptivity to acoustic disturbances radiating onto a flat plate with a sharp leading edge in the Mach 6 free stream is carried out. Different angles of incidence of fast and slow acoustic waves are considered. DNS results are compared with theoretical modeling of leading-edge receptivity and dow...

We present the results of linear and nonlinear simulations of hypersonic boundary layers over ultrasonic absorptive coatings consisting of uniform arrays of rectangular pores. Through direct numerical simulation of the two-dimensional Navier-Stokes equations, we explore the effects of coatings of various porosities and pore aspect ratios on the gro...

This paper addresses the fundamental issue: What is the upper limit of transition Reynolds number relevant to "absolutely quiet" free stream, in which the only source of unsteady disturbances is unavoidable thermal noise? To simulate thermal sources generating unstable boundary-layer modes, Langevin terms are included into the stress tensor and the...

Discrete spectrum of disturbances in high-speed boundary layers is discussed with emphasis on singularities caused by synchronization of the normal modes. Numerical examples illustrate different spectrum structures and jumps from one structure to another with small variations of basic-flow parameters. It is shown that this singular behavior is due...

Atmospheric and space launch stage separation depends on the aerodynamic interference between separating bodies. Quick means of estimating and controlling repulsion or attraction lift associated with this interaction are an important enabling technology to achieve the best compromise between launch separation rocket motor weight and safe staging. A...

Numerical simulations are performed to investigate the interaction of acoustic waves with an array of equally spaced two-dimensional microcavities on an otherwise flat plate without external boundary-layer flow. This acoustic scattering problem is important in the design of ultrasonic absorptive coatings for hypersonic laminar flow control. The ref...

Two-dimensional direct numerical simulation (DNS) of stabilization of supersonic boundary layers over a shallow grooved wavy plate at Mach=5.9 is carried out. Numerical experiments are conducted for propagation of disturbances generated by a suction-blowing actuator placed on the wall. Numerical data obtained for a flat plate are consistent with th...

The theoretically predicted second-mode instability is compared with the DNS data of Sandham and Ludeke for the non-gradient high-speed boundary layer flow on a thermally insulated wall covered by an ultrasonically absorptive coating (UAC). It is shown that for the coatings comprising equally spaced spanwise grooves and pores of rectangular crossse...

L. Mack (1969) carried out the inviscid stability analysis of high-speed boundary layers, and he found that in addition to the unstable mode having a viscous nature, there are other unstable discrete modes associated with acoustic perturbations ``trapped'' inside the boundary layer. In contemporary stability analysis of high-speed boundary layers a...

Numerical simulations of the linear and nonlinear two-dimensional Navier-Stokes equa-tions are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings consisting of a uniform array of rectangular pores (slots) with a range of porosities and pore aspect ratios. Based on our previous work, we employ a tempo-r...

Numerical simulations of the linear and nonlinear two-dimensional Navier-Stokes equations are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings consisting of a uniform array of rectangular pores (slots) with a range of porosities and pore aspect ratios. Based on our previous work, we employ a temporal...

†‡ Numerical modeling of vortex flow over a delta wing with sharp leading edges of 60 ο sweep angle has been performed at free-stream Mach number 1.5 and angles of attack from 0 ο to 30 ο . The flow field contains two strong vortices generated by the rollup of the shear layer emanating from the wing leading edges. Large radial and axial velocities...

Two-dimensional direct numerical simulation of stability of a near-wall laminar flow over a shallow wavy surface is carried out for the freestream Mach = 6. Numerical experiments are conducted for propagation of disturbances generated by a suction-blowing actuator placed on the wall. It is shown that high-frequency forcing excites unstable disturba...

Prediction of laminar-turbulent transition is important for aerothermal design and drag calculations of high- speed vehicles. In this work, two-dimensional direct numerical simulation (DNS) of receptivity to external acoustic disturbances radiating onto a flat plate with a sharp leading edge in the Mach 6 free stream is carried out. The surface tem...

A study was conducted to determine the felt-metal coating effect on disturbances in transitional and turbulent boundary layer on a sharp cone at zero angel in the Mach-6 impulse wind tunnel. The study used atomic-layer thermopile gauges (ALTP) for measurements of heat-flux disturbances on the solid and porous surfaces in a wide frequency band. The...

Numerical simulations are performed to investigate the interaction of acoustic waves with an array of equally-spaced two-dimensional micro-cavities on an otherwise flat plate without external boundary-layer flow. This acoustic scattering problem is important in the design of ultrasonic absorptive coatings (UAC) for hypersonic laminar flow control....

Ultrasonic absorptive coatings, consisting of regularly-spaced arrays of micro-cavities, have previously been shown to effectively damp second-mode instability for the purpose of delaying transition in hypersonic boundary lay-ers. However, previous simulations and stability analysis have used approx-imate porous-wall boundary conditions. Here we in...

Laminar flow control (LFC) technologies reduce heat-transfer rates as well as the weight and complexity of thermal protection systems (TPS). Previous theoretical and experimental hypersonic wind tunnel studies showed that the laminar run could be substantially increased using an ultrasonically absorptive coating (UAC) that suppresses the second mod...

Numerical simulations are performed to investigate the interaction of acoustic waves with an array of equally-spaced two-dimensional micro-cavities on an otherwise flat plate without external boundary-layer flow. This acoustic scattering problem is important in the design of ultrasonic absorptive coatings (UAC) for hypersonic laminar flow control....

Ultrasonic absorptive coatings, consisting of regularly-spaced arrays of micro-cavities, have previously been shown to effectively damp second-mode instability for the purpose of delaying transition in hypersonic boundary layers. However, previous simulations and stability analysis have used approximate porous-wall boundary conditions. Here we inve...

Two-dimensional direct numerical simulation (DNS) of receptivity to acoustic disturbances radiating onto a flat plate with a sharp leading edge in the Mach 6 free stream is carried out. Numerical data obtained for fast and slow acoustic waves of zero angle of incidence are consistent with the asymptotic theory. Numerical experiments with acoustic w...

To aid in the design of an ultrasonically absorptive coating (UAC) to be tested on a 7degree half-angle sharp cone in the CUBRC LENS I shock tunnel, parametric studies of the coating laminar-flow-control performance are conducted for Mach=7 and Mach=10 freestream conditions. The second-mode amplification factors, N, are calculated using the reduced...

The lift force acting on a slender body of revolution that separates from a thin wing in supersonic flow is analysed using Prandtl–Glauert linearized theory, scattering theory and asymptotic methods. It is shown that this lift is associated with multi-scattering of the wing-induced shock wave by the body surface. The local and global lift coefficie...

This report summarizes theoretical and CFD studies related to surface discharge to quench stall-slip departure due to asymmetric vortex shedding on aircraft nose tips, augment directional control/authority agility, and develop tailless capability. This approach offers adaptability in rapidly changing flight and mission conditions, constructional si...

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 o...