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Interaction of a shock wave with the boundary layer on a half-airfoil model is studied. The experiments are performed in a wind tunnel with the free-stream Mach number M ≈ 0.75 and stagnation pressure P₀ = 10⁵ Pa. The half-airfoil model is mounted on the wall of the test section of the wind tunnel. Pressure distributions over the model surface are obtained by a method with luminescent pressure transducers and by a method with pressure taps. The limiting streamlines on the model are visualized, and thermographic visualization is also performed. For experimental parameters, numerical simulations are performed with an approach based on using the Reynolds-averaged Navier--Stokes equations. The three-dimensional structure of the flow is analyzed, and significant differences in the measured and simulated results for the flow in corner separation regions are revealed.

Direct numerical simulations of propagation of disturbances generated by a heat source in a supersonic boundary layer interacting with an oblique shock wave are performed by the HyCFS-R hybrid code. The processes of excitation and evolution of unstable disturbances in the boundary layer, the influence of the incident shock wave on evolution of disturbances, and also the effect of disturbances on boundary layer separation and flow development in the separation region and in the laminar-turbulent transition region are studied. The influence of the duration of the thermal pulse on excitation and development of unstable waves in the boundary layer and interaction region is investigated. A case of disturbance generation by a pair of sources located at a certain distance from each other is considered. It is shown that reduction of the heat pulse duration leads to enhancement of the amplitudes of the first and second harmonics of the main unstable mode. For this reason, the disturbance spectrum in the interaction region changes, and flow turbulization is accelerated, which leads to reduction of the separation region size.

A two-dimensional problem of stationary nonlinear waves on the surface of a layer of finite-thickness ideal fluid is considered. The solution to the problem using the proposed technique includes the following steps. Firstly, the stream function trace is used to change the kinematic condition on the free surface. Secondly, the Bernoulli---Cauchy integral is applied to present the dynamic condition in a new form. Thirdly, an integral operator of the convolution type is introduced, which allows one to simplify the nonlinear boundary value problem of determining four functions of one variable, the main ones of which are a wave profile shape and a stream function trace at the zero horizon. This technique allows reducing the two-dimensional problem to a one-dimensional one. Two forms of the nonlinear dispersion relation are obtained: the dependence of the wave velocity on the amplitude of the fundamental harmonic of the wave and the dependence of the wave velocity on the wave amplitude. The cases of short and long waves are considered

In this paper, we have approximated the solutions of the Cahn-Hilliard equation (CH) with the logarithmic potential function which arises in the modeling of phase separation of binary alloys. The CH equation is a high-order nonlinear equation,consequently, utilizing a common difference scheme on the CH equation causes long stencil schemes. To resolve the faults of long stencil schemes, we split the CH equation to a second-order system under the Neumann boundary condition and we applied a second-order scheme based on the 2D Crank-Nicolson method to discrete it. The uniqueness and error estimation of the approximated solution is proved. Also, preserving the conservation of mass and decreasing the total energy are investigated. Finally, to confirm the theoretical results, three examples with various initial conditions are presented.

Perturbation propagation in a supersonic boundary layer on a straight parabolic wing is numerically simulated. Near the leading edge, a mass flow rate perturbation is introduced into the boundary layer, resulting in the formation of a first-mode wave packet, and the amplitude of the first mode increases downstream. It is shown that, upon reaching a critical amplitude, the perturbation begins developing nonlinearly and longitudinal structures appear. The nonlinear interaction of the boundary layer modes leads to the formation of a turbulent spot. The characteristics of the resulting spot with known data for gradient-free flows are compared

The properties of honey are studied experimentally.It is shown that the viscosity of honey decreases with an increase in its moisture content or temperature. Close results are obtained when measuring the surface tension coefficient of white honey using several methods: the drop weight method, the capillary ascent, and the detachment by an air bubble in a liquid. A formula is derivedthat allows one to estimate the dynamic viscosity of the liquid usingthe known surface tension coefficient and the known rate of recovery of an air bubble shape in a liquid after the bubble was stretched twice its size at the same measurement temperature

The paper describes an experimental study of the process in which a cluster of monodisperse droplets of isoparaffin oil ascends to the surface in distilled water in a range of Reynolds numbers Re = 200÷800. It is shown that the initial volume concentration of droplets in the cluster is one of the main parameters determining its dynamics. The study also touches upon the motion of two types of clusters, characterized by the presence or absence of collisions of the droplets contained in it. Experimental dependences of the rate of ascent of the droplet cluster on the Reynolds number are obtained for different values of the initial volume concentration of droplets. The limiting value of the initial volume concentration of droplets is determined, corresponding to the onset of cluster motion with a velocity exceeding the velocity of a single droplet

This paper touches upon the formation of thermomagnetic convection in a stratified magnetic colloid filling a Hele---Shaw cell placed in an external nonuniform magnetic field and heated from the side of a narrow edge in such a way that the constant field strength gradient is co-directed with the temperature gradient. The Galerkin method is applied to obtain critical magnetic Rayleigh numbers for the cases of monotonic convection and oscillatory convection arising due to the nonuniformity of the concentration of magnetic nanoparticles caused by thermal diffusion and magnetophoresis. In the case of oscillatory instability, the dependence of the neutral oscillation frequency on the mixture separation parameter and the concentration Rayleigh number is determined. For supercritical monotonic and oscillatory convection conditions, the current function, temperature, and concentration distributions are presented, and the behavior of the amplitudes of various spatial harmonics is investigated

The main goal of the present study is to investigate the mechanism of forced turbulization of the laminar boundary layer on a swept wing with domination of crossflow instability by means of using spanwise-periodic cylindrical trip devices. The experiments are performed with hot-wire anemometry in a low-turbulence wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk) at low subsonic free-stream velocities; a 25-degree swept wing is chosen as a model. Results of detailed precision measurements of the mean and fluctuating structure of the flow are obtained in a broad space range in 12 different regimes of measurements for five types of trip devices (and also without them) for two flow velocities. The range of the Reynolds numbers based on the trip height is from 565 and 3613. The present paper describes the first part of the study, i.e., the main scenarios of the transition to turbulence induced by trip devices. They are demonstrated to be highly effective. Subsequent studies will be described in Part 2 of the paper.

An incompressible gas flow past a two-dimensional backward-facing step on the flat plate surface is experimentally studied under the conditions of a controlled low-frequency action on the separated flow. It is found that flow oscillations whose frequency is smaller by an order of magnitude than the frequency typical for convective instability of the separated boundary layer induce significant changes of the time-averaged and fluctuating characteristics of the flow in the separation region.