The complex flow of a supersonic jet (Mach number 2.4-2.5) around the blunt aerodynamic body (consisting of a cylinder with a diameter of 16 mm and a truncated cone) was studied using the high-speed shadowgraph technique and computer vision-based visual data processing. The problem considered is directly related to the rocket and space systems stages safe separation problem in a sufficiently dense atmosphere. For systems with a sequential arrangement of stages, their separation often occurs under the rocket engine jet action. The occurrence of lateral forces in violation of axial symmetry can lead to overturning of the discarded stage and undesirable interaction with the outgoing stage. The goals of the paper were to study the pulsation characteristics of the incoming supersonic jet streamlining the body, as well as the pulsations of the bow shock wave in both axisymmetric and asymmetric flows. The recording frame rate in the experiments was up to 775 000 fps. Computer vision and various machine learning approaches were used to process a large number of shadowgraph images. Canny edge detection and Hough transform, as well as a convolutional neural network (CNN) based on YOLOv2 architecture, were used to automatically track the position of the bow shock relative to the body. Jet sound generation was studied - the amplitude dependence on the distance from the nozzle and the evolution in time. The position of the bow shock relative to the streamlined body and flow pulsations over time were analyzed. Bow shock pulsation spectra at zero angle of attack were compared to those at a small angle of attack (alpha = 2.5 degrees -3 degrees). The power spectral density was also estimated. The slope of the spectra for the zero angle of attack case was found to be horizontal and the spectra for the small angle of attack case had a slope close to -5/3. The strongest of the measured bow shock frequencies were found to be close to those of the jet mixing layer pulsations. The hardware signal spectrum was also measured and this signal can be considered as noise. The described approach makes it possible to obtain the physical characteristics of the flow at any point of interest. It was also shown that the automation of flow visualization experiments using computer vision techniques allows to increase the speed of data processing and obtaining new physical information, which may be important for engineers developing aircraft and spacecraft technologies.

The effect of a porous wingtip on tip vortex formation and properties in a supersonic flow is studied. It is established that a porous wingtip has a considerable effect on the vortex structure and parameters reducing its intensity.

New compact hyperbolic quasi-gas-dynamic system of equations (CHQGD) is derived from kinetic models for the one-particle distribution function. The system differs from the Navier–Stokes equations by a second-order value in the Knudsen number. The presence of second time derivatives makes the CHQGD system hyperbolic, in contrast to the Navier–Stokes equations. The system of CHQGD equations allows one to construct efficient – including parallel – computational algorithms for modeling viscous flows.

We consider a compact version (the CQGD system) of the quasi-gasdynamic system. All algorithms that have been used to approximate the spatial derivatives in the Navier–Stokes equations can also be applied to the CQGD system. At the same time, the use of the CQGD system permits significantly improving the stability of explicit schemes, which is important for ensuring high-performance parallel computations. As examples of the use of algorithms based on the CQGD system, we present the results of computations of a laminar boundary layer on a plate and of a hypersonic laminar separated flow in a compression angle.

In this paper numerical calculations of a wingtip vortex for various wing angles of attack are presented, and the resulting flow modes are compared with each other and with the experimental data. Numerical computations were performed at the Keldysh Institute of Applied Mathematics, making use of the Spalart-Allmaras turbulence model. Experiments were carried out at the Institute of Theoretical and Applied Mechanics, Siberian Branch (SB), Russian Academy of Sciences (RAS), Khristianovich, Russia.

The features identified by the wavelet algorithm based on Euler and Reynolds model calculations with the k-ɛ model of turbulence and the use of methods of through count are analyzed. The studies have shown that in a viscid fluid, the structures corresponding to shock waves in an ideal fluid are clearly manifested, and on them the Hugoniot conditions are fulfilled to a high accuracy. Besides, the additional structures corresponding to vortices, as well as boundary and mixing layers, are localized in the viscid fluid.

Results of experimental studies and numerical calculations of aerodynamic characteristics of a supersonic flow around a body of revolution with a gas-permeable porous nose cone and an internal duct are presented. At a flow velocity corresponding to the Mach number M = 3, the body considered is found to have a lower drag coefficient ( approximately by 9%) than a similar body impermeable for the gas and a lower streamwise static stability .

An algorithm that can detect and classify singularities of gas-dynamic fields obtained by numerical simulation is constructed. The algorithm employs wavelet expansion of the original fields followed by analyzing the obtained coefficients. The ideas of this approach were originally proposed in [1–3]. The algorithm that can detect and classify discontinuities and is linear in terms of computational complexity is proposed and tested. It expands the gas-dynamic components with respect to the basis of complexvalued symmetric orthogonal wavelets and uses classical real-valued Daubechies wavelets to postprocess them. The algorithm was applied to analyze two-dimensional gas flow structure when the flow is controlled by local heat release.

Methods of interpreting data on the effect of the solvent on the spectral characteristics of molecules are critically compared. It is shown that the effect of field-induced intermolecular interaction in solutions on molecular spectra can be calculated in terms of the London–Debye–Keesom pair potential. 145 references.