T. V. Poplavskaya

Engineering modeling of the laminar–turbulent transition: Achievements and problems (Review)

Currently available methods of computing the laminar–turbulent transition (LTT), including methods used in gas-dynamic software packages, are analyzed from the viewpoint of LTT simulation accuracy.

Influence of vibrational relaxation on perturbations in a shock layer on a plate

The influence of excitation of molecular vibrational degrees of freedom on the mean flow and perturbation development in a hypersonic (M = 6–14) viscous shock layer is studied. The layer originates on a plate placed in a flow of air, carbon dioxide, or their mixture at high stagnation temperatures (2000–3000 K). The mean flow and pressure pulsation on the surface of the plate are measured in an IT-302M pulsed wind tunnel (Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences). Numerical simulation is carried out in terms of a model of a thermally perfect gas using the ANSYS Fluent program package based on solving nonstationary two-dimensional Navier-Stokes equations. External flow perturbations are introduced into the computational domain in the form of plane monochromatic acoustic waves using UDF modules built in the computational code. It is shown that the excitation of vibrational degrees of freedom in carbon dioxide molecules considerably influences the position of the head wave and intensifies perturbations in contrast to air in which the fraction of vibrationally excited molecules is low at the same parameters of the oncoming low. The influence of the excitation of vibrational degrees of freedom is studied both for equilibrium gas and for a vibrationally nonequilibrium gas. Nonequilibrium vibrational degrees of freedom are simulated using a two-temperature model of relaxation flows in which the time variation of the vibrational energy is described by the Landau-Teller equation with regard to a finite time of energy exchange between vibrational and translational-rotational degrees of freedom of molecules. It is found that the vibrational nonequilibrium has a damping effect on perturbations.

Modeling of a supersonic flow around a cylinder with a gas-permeable porous insert

Results of an experimental and numerical study of a supersonic (M∞ = 4.85) flow around a streamwise-aligned cylinder with a gas-permeable porous insert on the frontal face in the range of Reynolds numbers ReD = (0.1–2.0) · 105 are presented. The numerical study is performed by using the Ansys Fluent software system and a porous medium model based on a quadratic law of filtration. The parameters of the quadratic dependence are calculated on the basis of experimental data for an air flow in a porous material. Flow fields are obtained, and the wave drag of the model is calculated as a function of the porous insert length and the Reynolds number. Results of numerical simulations are compared with wind tunnel measurements.

The efficiency of the method of sound-absorbing coatings in vibrationally excited hypersonic flow

We have studied the effect of a porous sound-absorbing insert on the intensity of pressure pulsations in the high-temperature hypersonic flow of carbon dioxide past the surface of a plate oriented at a 10.2° angle of attack. The mode composition of disturbances in the flow core of a pulsed wind tunnel has been experimentally determined, which is dominated by acoustic disturbances of a fast mode. It is established that, under the action of acoustic disturbances of the fast mode on the shock layer, the sound-absorbing insert reduces the intensity of pressure pulsations on the plate surface as compared to a continuous surface. The experimental data are compared to the results of numerical simulations.

Effect of sound-absorbing materials on intensity of disturbances in the shock layer on a flat plate aligned at an angle of attack

Results of a numerical and experimental study of characteristics of disturbances in a hypersonic shock layer on a flat plate covered by a sound-absorbing coating and aligned at an angle of attack are presented. Experiments and computations are performed for the free-stream Mach number M∞ = 21 and Reynolds number ReL = 6 · 104. A possibility of suppressing pressure fluctuations in the shock layer at frequencies of 20–40 kHz with the use of tubular and porous materials incorporated into the plate surface is demonstrated. Results of numerical simulations are found to be in good agreement with experimental data.

A numerical study of non-equilibrium flows with different vibrational relaxation models

Comparative analysis of a widely used Landau–Teller formula for small deviations from thermal equilibrium and its generalized form, derived from the kinetic theory of gaseous, for an arbitrary deviation from the thermal equilibrium is performed by numerical simulation. Thermally non-equilibrium flows of carbon dioxide near a sharp-edged plate, pure nitrogen flows between two symmetrically located wedges, and the N2/N mixture flow with vibrational relaxation and dissociation over a cone have been considered. A comparison has been performed with the available experimental data.

Nonlinear wave processes in a hypersonic shock layer

Nonlinear disturbance development in a hypersonic flat-plate shock layer (M∞ = 21, ReL = 1.44×105) exposed to external-flow slow-mode acoustic perturbations at one or several frequencies is studied on the basis of the numerical solution of the Navier-Stokes equations. The mean flow distortion by disturbances and the nonlinear self-interaction between spectral modes is investigated by varying the initial amplitudes of the acoustic waves introduced. The appearance of combination frequencies, both summarized and subtracted, and their interaction with each other is shown to exist.

Stability of the Hypersonic Shock Layer on a Flat Plate

The stability of hypersonic viscous gas flow in a shock layer in the neighborhood of a flat plate is considered. The stability of the velocity, temperature, density, and pressure profiles calculated on the basis of the complete viscous shock layer equations is investigated within the framework of the linear stability theory with allowance for the shock wave relations. The calculated perturbation growth rates and phase velocities are compared with the experimental data obtained by means of electron-beam fluorescence.

Bispectral analysis of numerical simulations of wave processes in hypersonic shock layers

Results of numerical simulations of the evolution of disturbances in a hypersonic shock layer on a flat plate at high Mach numbers (M∞ = 21) and moderate Reynolds numbers (ReL = 1.44 · 105) are analyzed by an adapted method of bispectral analysis. All basic types of nonlinear interactions are obtained. The calculated results are compared with experimental data.

A Similarity Criterion for Supersonic Flow Past a Cylinder with a Frontal High-Porosity Cellular Insert

We have experimentally and numerically studied the influence of the ratio of the diameter of a cylinder with a frontal gas-permeable porous insert made of nickel sponge to the average pore diameter in the insert on the aerodynamic drag of this model body in supersonic airflow (M∞ = 4.85, 7, and 21). The analytical dependence of the normalized drag coefficient on a parameter involving the Mach number and the ratio of cylinder radius to average pore radius in the insert is obtained. It is suggested to use this parameter as a similarity criterion in the problem of supersonic airflow past a cylinder with a frontal high-porosity cellular insert.