Influence of streamwise slots with the orientation angle φ = 0 and various depths h (corresponding Reynolds number Reh = 0–2000) on the stability of the supersonic (M = 2) flat-plate boundary layer with relation to natural disturbances of the first (vorticity) instability mode driving laminar-turbulent transition was investigated experimentally. Experiments shown that such kind of disturbances can be stabilized by small-depth streamwise slots, wherein the maximum stabilization occurs at the Reynolds number (based on the slot depth) of about Reh ≈ 1000.

The paper discusses experimental results on the wave train development in a longitudinal trace in the flat plate boundary layer at Mach 2.5. An analysis of the spatiotemporal distributions and frequency-wave spectra of pulsations, as well as their wave characteristics in the linear and weakly nonlinear phase of the wave train development in a homogeneous and inhomogeneous boundary layer at a fixed power of the controlled disturbances source has been carried out. During the analysis of the results, no subharmonic resonance was observed. Expansion into the wave spectrum of a stationary in- homogeneity and experimental data on wave characteristics and disturbance spectra made it possible to propose options for wave interaction for oblique breakdown.

The results of experimental measurements are presented to assess the correlation characteristics of disturbances in the boundary layer of a flat plate with a sharp leading edge and pulsations of the incoming flow in cases of natural pulsations and influence of an N-wave for Mach 2 on the leading edge. The parameters of the cross-correlation of signals from two constant-temperature anemometry (CTA) are obtained digitally. The frequency ranges with apparent correlation between the mass flow rate pulsations measured by the probes are determined.

A passive control method for supersonic boundary-layer transition on a swept wing using longitudinal roughness is proposed. Tests were carried out to examine the effect of distributed roughness on the development of flow peturbations and on the laminar-turbulent transition. The method makes it possible to manipulate the transition in a wide range, bringing it either closer to the leading edge of the wing by 30 % or delaying it by 40%.

The action of a pair of weak shock waves on a supersonic boundary layer on a swept flat plate with a bluntness radius of the leading edge equal to 2.5 mm at the Mach number 2 is experimentally studied. Transverse hot-wire measurements are performed in the boundary layer with a fixed distance of the probe from the model surface. It is found that a change in the sweep angle of the leading edge from 35 to 45 degrees reduces the intensity of the action of the weak shock waves on the boundary layer flow. As the sweep angle of the leading edge increases to 50°, the weak shock waves no longer affect the flow in the supersonic boundary layer on the swept plate.

A pioneering experimental study of the influence of distributed suction of a supersonic boundary layer on a flat plate on its stability to controlled (artificial) disturbances at the freestream Mach number M∞ = 2 is performed. Experimental results are compared to numerical predictions, and good quantitative agreement is observed. The conclusions of the linear stability theory that suction of the type considered in the study stabilizes the flow in a supersonic boundary layer are experimentally validated; moreover, the stabilizing effect of suction is more pronounced than the destabilizing effect of surface porosity.

The present study is aimed at searching for mechanisms of wave interaction in a supersonic boundary layer on a flat plate with the flow being distorted by a streamwise disturbance generated on a sharp leading edge by a pair of weak shock waves. The space and time distributions and the frequency-wave spectra of oscillations and their wave characteristics in the linear and weakly nonlinear phases of wave train development in a nonhomogeneous boundary layer under conditions of a fixed power of the local source of controlled disturbances are analyzed. Based on experimental results, possible variants of wave interaction in a supersonic boundary layer on a flat plate in the region of the longitudinal wake generated by an N-wave are proposed.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Boris V. Smorodsky, Sergey A. Gaponov, Vladimir I. Lysenko, Alexander D. Kosinov, Michael I. Yaroslavtsev; Influence of surface sublimation on supersonic flat plate boundary layer stability. AIP Conference Proceedings 16 February 2023; 2504 (1): 030058. https://doi.org/10.1063/5.0132285 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

This work is devoted to the study of the influence of the small angles of attack and external disturbances on the position of the laminar-turbulent transition in the supersonic boundary layer on swept wings. The experiments were carried out in a low-noise supersonic wind tunnel T-325 of the ITAM SB RAS at Mach numbers M = 2 and M = 2.5 on two wing models with leading edge swept angles χ = 45˚ and χ = 72˚. The measurements were carried out by the hot-wire probe or Pitot tube. External disturbances were generated by a wire placed ahead of the nozzles in the subsonic part of the flow. It was shown that external disturbances and small angles of attack strongly affect the position of the laminar-turbulent transition. The laminar-turbulent transition on a wing model with a subsonic leading edge occurs earlier than on a wing model with a supersonic leading edge at low noise conditions. The influence of leading edge swept angle χ on transition Reynolds number was not observed at noisy conditions.

We present the new (for Mach numbers М = 3 and 3.5) and generalizing (for Mach numbers from 2 to 4) results of experimental investigations on the effect of small angles of attack on laminar-turbulent transition in the supersonic boundary layer on a swept wing with the leading-edge slip angle of 72°. The angle-of-attack variation has a strong effect on the transition Reynolds number. The transition Reynolds number decreases with increase in the Mach number. The measurements were carried out by means of a constant-temperature hot-wire anemometer using the proven procedure of determining the transition location. The eN method is used for the first time for numerically estimating the transition Reynolds numbers in the supersonic boundary layer on a swept wing with the leading-edge slip angle of 72°. The growth of the amplitudes of the steady and unsteady modes of the boundary layer crossflow are calculated in accordance with the linear stability theory, within the framework of the Lees–Lin system of equations. The numerical results indicate that, in accordance with the experimental results, laminar-turbulent transition in the boundary layer on the model swept wing is governed by the growth of stationary modes of the crossflow instability.

Stationary disturbances in a free supersonic flow caused by two-dimensional roughness in a turbulent boundary layer on a wall were investigated using numerical simulation in the FlowVision software package. Calculations were performed for cases where the roughness heights were significantly smaller than the thickness of the boundary layer. In order to reduce the numerical oscillations, the computational grid has been adapted to the perturbation fronts by means. It was found that a disturbance in the form of a small amplitude N-wave is formed in the flow above the boundary layer. The effect of roughness height on disturbances formed in a free flow was studied. It was found that as the roughness height increases, there is an observed increase in the amplitude and spatial scale of the disturbance. It was also found that the gradient of the flow parameters between the disturbance fronts remains practically unchanged for all roughness heights considered. The numerical results were verified with experimental data. A strong agreement was achieved between the simulation and experimental result.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation A. A. Yatskikh, A. D. Kosinov, N. V. Semionov, Yu. G. Ermolaev, L. V. Afanasev, V. L. Kocharin, A. V. Shmakova; Experimental studies of pulsations of the boundary layer of swept wings with periodic roughness at M = 4. AIP Conference Proceedings 16 February 2023; 2504 (1): 030068. https://doi.org/10.1063/5.0132320 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

The paper describes a digital signal processing technique for determining the relationship between disturbances in a supersonic flow and pulsations of the boundary layer of a flat plate model. Estimates of the error of the proposed data processing method are given, the results of an experiment conducted to demonstrate the method on real data are presented.

Results of experimental studies are applied to compare the spatiotemporal amplitude distributions of controlled fluctuations in a linear and a weakly nonlinear phase of the development of a wave train in a homogeneous and an inhomogeneous boundary layer on a flat plate at a Mach number M = 2. (The flow is inhomogeneous due to a longitudinal steady perturbation generated by a pair of weak shock waves. Controlled perturbations are generated locally from the surface at a fixed power of a high-frequency glow discharge inside the model.) It is revealed that the inhomogeneity of the flow changes the mechanism of interaction of subharmonic perturbations. It is shown that the spatial synchronism of fluctuations of subharmonic frequency is violated in the center of the wave train.