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 receptivity instability. It is shown that extension subsonic low-supersonic concepts prediction methods hypersonic speeds not straightforward. The discussion focuses on theoretical models providing insights into physics instability helping make proper decisions control strategies.

A second-mode stability analysis has been performed for a hypersonic boundary layer on wall covered by porous coating with equally spaced cylindrical blind microholes. Massive reduction of the second mode amplification is found to be due disturbance energy absorption layer. This stabilization effect was demonstrated experiments recently conducted sharp cone in T-5 high-enthalpy wind tunnel Graduate Aeronautical Laboratories California Institute Technology. Their experimental confirmation...

Experimental and theoretical studies of the effect an ultrasonically absorptive coating (UAC) on hypersonic boundary-layer stability are described. A thin fibrous absorbent material (felt metal) was selected as a prototype practical UAC. Experiments were performed in Mach 6 wind tunnel half-angle sharp cone whose longitudinal half-surface solid other covered by porous coating. Hot-wire measurements 'natural' disturbances artificially excited wave packets conducted both surfaces. Stability...

The discrete spectrum of disturbances in high-speed boundary layers is discussed with emphasis on singularities caused by synchronization the normal modes. Numerical examples illustrate different spectral structures and jumps from one structure to another small variations basic flow parameters. It shown that this singular behavior due branching dispersion curves region. Depending locations branch points, contains an unstable mode or two. In connection this, terminology used for instability...

Recently performed linear stability analyses suggested that transition could be delayed in hypersonic boundary layers by using an ultrasonically absorptive surface to damp the second mode (Mack mode). Boundary-layer experiments were on a sharp 5.06-deg half-angle round cone at zero angle of attack T5 Hypervelocity Shock Tunnel test this concept. The was constructed with smooth around half circumference (to serve as control) and acoustically porous other half. Test gases investigated included...

Two-dimensional direct numerical simulation (DNS) of receptivity to acoustic disturbances radiating onto a flat plate with sharp leading edge in the Mach 6 free stream is carried out. Numerical data obtained for fast and slow waves zero angle incidence are consistent asymptotic theory. experiments non-zero angles reveal new features disturbance field near edge. The shock wave, which formed owing viscous–inviscid interaction, produces profound effect on excitation boundary-layer modes. DNS...

Abstract Numerical simulations of the linear and nonlinear two-dimensional Navier–Stokes equations, stability theory are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings. The porous coatings consist a uniform array rectangular pores (slots) with range porosities pore aspect ratios. For numerical simulations, temporally (rather than spatially) evolving considered we provide evidence that this approximation is appropriate for slowly growing...

The linear stability analysis predicts that the Mack second mode propagating in boundary layer on a sufficiently cold plate can radiate acoustic waves into outer inviscid flow. This effect, which is called as spontaneous radiation (or emission) of sound, associated with synchronization slow continuous spectrum. theoretical predictions are confirmed by direct numerical simulations wave trains and packets flat at free-stream Mach number 6 wall-to-edge temperature ratio $T_{w}/T_{e}=0.5$ . A...

Theoretical and experimental studies of hypersonic boundary-layer stabilization using a passive porous coating regular microstructure are discussed. Propagation disturbances inside pores is simulated with linear acoustic theory including the gas rarefaction effect. This model provides boundary conditions for stability analysis on wall. Experiments were conducted in Mach 6 wind tunnel 7-deg half-angle sharp cone whose longitudinal half-surface solid other covered by perforated sheet...

Abstract Laminar–turbulent transition in the boundary layer at supersonic speeds can be initiated by small solid particles present free stream. Particulates interacting with boundary-layer flow generate unstable wavepackets related to Tollmien–Schlichting (TS) waves. The latter grow downstream and ultimately break down turbulent spots. This scenario of TS-dominated is modelled using Mack amplitude method. A theoretical model describing receptivity mechanism developed predict initial spectrum...

A localized heating or cooling effect on stability of the boundary-layer flow a sharp cone at zero angle attack and freestream Mach number 6 is analyzed. Experiments were carried out in Transit-M wind tunnel Institute Theoretical Applied Mechanics (Novosibirsk, Russia) for different heating/cooling intensities Reynolds numbers. The mean flows with are calculated using axisymmetric Navier–Stokes equations. These solutions used spatial linear analysis to estimate transition onset points...

A simple extension of the classic Görtler–Hämmerlin (1955) (GH) model, essential for three-dimensional linear instability analysis, is presented. The extended model classifies all disturbances in this flow by means symmetric and antisymmetric polynomials chordwise coordinate. It results one-dimensional eigenvalue problems, a temporal or spatial solution which, presented herein, demonstrated to recover otherwise only accessible partial-derivative problem (the former also solved here) direct...

Numerical simulations are performed to investigate the interaction of acoustic waves with an array equally spaced two-dimensional microcavities on otherwise flat plate without external boundary-layer flow.This scattering problem is important in design ultrasonic absorptive coatings for hypersonic laminar flow control.The reflection coefficient, characterizing ratio reflected wave amplitude incident amplitude, computed as a function frequency and angle incidence, different porosities, at...

Direct numerical simulations of a three-dimensional wave packet propagating over 5.5 deg compression corner at the freestream Mach number 5.373 are carried out. The Navier–Stokes equations integrated using an implicit finite volume shock-capturing method with second-order approximation in space and time. After computing laminar flowfield, unsteady disturbances imposed onto steady solution via local suction blowing on wall surface. undisturbed boundary layer separates upstream reattaches...

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 flow can excite wavepackets first- and/or second-mode instability. The packets grow downstream, reach threshold amplitude and ultimately break down turbulent spots. A numerical model is developed simulate excitation unstable by spherical solid particulates. As an example,...

Analytical solutions describing propagation of monochromatic acoustic waves inside long pores simple geometries and narrow flat slits are obtained with accounting for gas rarefaction effects. It is assumed that molecular nature important in Knudsen layers near solid boundaries. Outside the layers, continuum approach used. This model allows extension analysis to regions low pressures microscopic cross-sectional sizes channels. The problem solved using linearized Navier-Stokes equations...

An initial-value problem is analyzed for a two-dimensional wave packet induced by local disturbance in hypersonic boundary layer. The solved using Fourier transform with respect to the streamwisecoordinateandLaplacetransform respectto time. temporal continuous spectrum isrevisited, and uncertainty associated overlapping of continuous-spectrum branches resolved. It shown that thediscretespectrum’ s dispersion relationship isnonanalyticbecause thesynchronization thee rst mode vorticity/entropy...

Ultrasonically absorptive coatings (UAC) can suppress the second-mode instability in hypersonic boundary layer and thereby delay laminar-turbulent transition. Theory numerical simulations indicate that this stabilization effect essentially depends on UAC thickness. It is expected optimal may be several times thinner than it was assumed before. To validate these findings, thickness investigated a sharp cone Mach=6 wind tunnel. The comprise layers of stainless still wire mesh. Their...

Abstract Two-dimensional direct numerical simulation (DNS) of the receptivity a flat-plate boundary layer to temperature spottiness in Mach 6 free stream is carried out. The influence parameters on process studied. It shown that spots propagating near upper boundary-layer edge generate mode F inside layer. Further downstream synchronized with unstable S (Mack second mode) and excites latter via inter-modal exchange mechanism. Theoretical assessments amplitude are made using biorthogonal...