Ivan V. Egorov

Receptivity of a hypersonic boundary layer over a flat plate with a porous coating

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 waves of non-zero angles of incidence reveal new features of the disturbance field near the plate leading edge. The shock wave, which is formed near the leading edge owing to viscous-inviscid interaction, produces a profound effect on the acoustic near field and excitation of boundary-layer modes. DNS of the porous coating effect on stability and receptivity of the hypersonic boundary layer is carried out. A porous coating of regular porosity (equally spaced cylindrical blind micro-holes) effectively diminishes the second-mode growth rate in accordance with the predictions of linear stability theory, while weakly affecting acoustic waves. The coating end effects, associated with junctures between solid and porous surfaces, are investigated.

Stabilization of a Hypersonic Boundary Layer Using a Wavy Surface

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 placed on the wall. It is shown that the high-frequency forcing excites unstable waves in the flat-plate boundary layer. These waves are relevant to the second-mode instability. The wavy wall damps the disturbances in a high-frequency band while it enhances them at lower frequencies. Stability experiments are conducted in the Institute of Theoretical and Applied Mechanics Tranzit-M shock tunnel under natural freestream conditions. The measured disturbance spectra are similar to those predicted numerically. They contain a peak associated with the second-mode instability. This peak is damped by the wavy wall, while a marginal increase of the disturbance amplitude...

Direct numerical simulation of supersonic boundary-layer stabilization by porous coatings

Two-dimensional direct numerical simulation (DNS) of the porous coating stabilization effect is carried out for near-wall flows over a flat plate, sharp cone and compression corner at freestream Mach numbers 5-6. Numerical data obtained for disturbances propagating in the boundary layer on a flat plate agree satisfactory with the linear stability theory (LST). The coating end effects, which are associated with discontinuity of boundary conditions at the juncture between solid and porous walls, are considered. It is found that the end effects are localized over 2-3 disturbance wavelength and can be neglected in calculations of the integral performance of porous coatings. Receptivity of supersonic boundary layer to fast and slow acoustic waves is modeled. It is shown that the porous coating weakly affects acoustic disturbances and initial amplitudes of the boundary-layer modes, while it strongly suppresses the second-mode amplification. For the compression corner flow, DNS shows that the porous coating weakly affects high-frequency disturbances in the separation region and strongly stabilizes them in the reattached boundary layer downstream from the separation bubble. These numerical studies confirm robustness of the porous coating stabilization concept.

Direct Numerical Simulations of Supersonic Boundary Layer Receptivity to Acoustic Disturbances

Two-dimensional direct numerical simulation of receptivity to acoustic disturbances radiating a flat plate in 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 conducted for acoustic waves of the angles of incidence ± reveal new features of the disturbance field in the leading-edge vicinity, which may play important role in the receptivity process. It is shown that the shock wave, which is formed near the plate leading edge due to viscous-inviscid interaction, produces a profound effect on acoustic near field and receptivity. 45°

Two-Dimensional Shock-Wave/Boundary-Layer Interaction in the Presence of Entropy Layer

Results of experimental and numerical study of gas flow and heat transfer in the region of interference of the impinging oblique shock wave with the near-wall flow on sharp and blunt plates are presented. The study is performed for the freestream Mach numbers from 5 to 10 and Reynolds numbers from 0.3×106 to 27×106 corresponding to the laminar and turbulent undisturbed boundary layers. The plate bluntness, location of the impinging shock, and the shock strength are varied. It is shown that the plate bluntness significantly reduces the heat transfer in the interference region due to the increase of separation-zone size and the reduction of gas density in the high-entropy layer. As the plate bluntness increases the heat transfer decays to a certain threshold value of the bluntness radius. The bluntness effect on the heat transfer increases and the bluntness threshold value decreases with the freestream Mach number.

Self-Noise of the MET Angular Motion Seismic Sensors

Interest to angular motion seismic sensors is generated by an expectation that direct measurement of the rotations, associated with seismic signals, would allow obtaining more detailed and accurate information from them. Due to the seismic signals low intensity a self-noise of the sensors is one of the most crucial parameters, characterizing their performance. In seismic applications the molecular-electronic transfer (MET) technology is considered as one of the most promising technologies for the rotations measurements. In this research we have developed a noise model for the MET angular sensors. The experimental part of the research which fully agrees with theoretical data includes the instrument self-noise measurement in quite locations. Based on the modelling we have revealed the directions of further research to improve the MET angular sensors performance.

High-Speed Boundary-Layer Stability on a Cone with Localized Wall Heating or Cooling

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 Reynolds numbers. The mean flows with localized heating/cooling are calculated using axisymmetric Navier–Stokes equations. These solutions are used for the spatial linear stability analysis to estimate the transition onset points using the eN method. Direct numerical simulations of two-dimensional disturbances propagating in the boundary layer through the cooled/heated region are performed. The experiment and computations showed similar qualitative trends. The localized cooling decreases the second-mode amplitude and delays transition. The heating produced an opposite effect, which is less pronounced.

Direct numerical simulation of supersonic boundary layer stabilization using grooved wavy surface

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 the linear stability theory (LST) and stability experiments in the “Transit-M” wind tunnel of the Institute of Theoretical and Applied Mechanics. It is shown that high-frequency forcing excites unstable disturbances in the flat-plate boundary layer relevant to the second-mode instability. The wavy wall leads to damping of these disturbances in a wide frequency band of the forcing.

RECEPTIVITY OF SUPERSONIC BOUNDARY LAYER ON A BLUNT PLATE TO ACOUSTIC DISTURBANCES

Receptivity of supersonic boundary layer to acoustic disturbances interacting with a blunt leading edge of a flat plate is studied using a combined asymptotic and numerical approach. A relationship between the receptivity coefficients for sharp and blunt leading edges is established using the concept of effective length. For the case of receptivity to fast acoustic waves at free-stream Mach number 6, it is shown that even small bluntness leads to significant decreasing of the receptivity level. Nomenclature C = coupling coefficient E = receptivity coefficient F = frequency parameter L = streamwise length scale ef l = effective length b l = wavelength coefficient M = freestream Mach number p = pressure disturbance r = nose radius ** Re /

Investigations of laminar-turbulent transition on a sharp cone with localized heating or cooling in high-spee d flow

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 locati ons of the heating/cooling strip are considered. The steady-state laminar flow solution is calculated using the axisymmetric Navier-Stokes equations to provide the mean flow fi eld. The spatial stability analysis is performed for two-dimensional disturbances associated with the Mack first and second modes. The transition onset points are estimated us ing the e N method. In this framework, the heating/cooling effect on the transition onset is i nconclusive. The heater (or cooler) may cause earlier or later transition depending on the choice of critical N-factor. Direct numerical simulations and experiments are needed to clarify this situation.