Fluid Dynamics最新文献

A series of experiments are conducted with the use of a shock tube at the Institute of Mechanics, Moscow State University to determine radiation absorption spectra in shock-heated oxygen in the wavelength range of 213–260 nm at a gas pressure of 1 Torr and shock wave velocities ranging from 3.4 to 4.5 km/s. Based on a comparison of the experimental data with the results of calculations using a spectral-kinetic model, the effect of bound–bound and bound–unbound transitions in the Schumann–Runge system on the absorption properties of oxygen is analyzed.

Rarefied gas flows through a planar periodic system of rectangular channels (membrane) are analyzed in a wide range of Knudsen numbers. The problem is studied based on the numerical solution of the kinetic equation with the Shakhov S-model collision integral and the Navier–Stokes equations of the compressible medium. The main attention is paid to the calculation of the mass flow rate as a function of the permeability, the relative channel length, and the rarefaction parameter.

The vortex systems formed behind a delta wing in supersonic flow are considered. The dependence of these structures on the attack angle and the incoming flow Mach number is studied, together with their effect on the aerodynamic properties of a downstream straight wing. The regimes with M = 2 and 3 and α = 10°, 14°, and 20° are considered. The numerical data are obtained using the hybrid multiprocessor supercomputer system K-60 in the Common Use Center of the Keldysh Institute of Applied Mathematics of the Russian Academy of Sciences.

The effect of body truncation with the formation of a leading face or an edge on the aerodynamic drag is investigated. In the former case the cross-sectional shape of the body (circular, elliptic, or diamond) does not change, while the area is determined by the power-law dependence on the longitudinal coordinate. In the latter case, the cross-sectional shape changes from a rectilinear segment in the initial section to a circle in the end section. The bodies thus constructed have the same length and the base area. The body drag is calculated using the Newton formula for the pressure coefficient.

Supersonic viscous gas flow past the upper surface of a blunt finite-length plate is considered in the interaction regime. The temperature factor effect on the pressure disturbances initiated by mounting a wedge at the plate end, the aerothermodynamic flow characteristics, and the disturbance propagation upstream are investigated. Numerical calculations are carried out within the framework of the solution of the stationary two-dimensional Navier–Stokes equations.

An important component of space flight safety is the effectiveness of thermal protection of the surface of reusable spacecraft, which is ensured by the use of modern materials with the lowest catalytic activity when interacting with the atmospheric gas mixture. Based on a stage-by-stage heterogeneous kinetics of the interaction between a dissociated gas mixture and the surface of β-cristobalite, a numerical simulation of the supersonic multicomponent nonequilibrium-dissociated air flowing around a cylindrical model is performed in the framework of Navier–Stokes equations taking into account the chemical reactions in the flow under the conditions of heat exchange experiments on with the use of a VGU-4 induction RF plasmatron (developed at the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPMech RAS)). A comparative analysis of the calculations of the flow in the plasmatron with and without taking into account nitrogen oxide formation on the streamlined surface has been performed to show that it is required for taking into account the heterogeneous recombination of nitrogen oxide in boundary conditions. The dependence of flow characteristics on the density of adsorption sites is established over a broad range, representing regimes from non-catalytic to full catalytic behavior. The contribution made by diffusion and thermal conductivity processes to the heat flux towards the surface is demonstrated for different modes of gas interaction with the surface material.

The motion and ablation of a meteoroid breaking up into a large number of fragments are considered. At the first stage, the fragments move with a common shock wave, before dispersing to a distance sufficient for independent motion. We consider models of cloud of fragments that simulate the meteoroid disruption at this stage: the two-parameter model, which takes into account changes in the cloud shape and density, and simple models used in the literature that do not take these effects into account. The models differ in the equations for the lateral expansion rate of the cloud. The unrealistically strong increase in the midsection radius, which is given by simple models, is usually limited in the literature to a certain specified value. The effect of this midsection radius cutoff in different fragment cloud models on the results of modeling the energy deposition of the Chelyabinsk superbolide is studied. For this purpose, the equations of the physical theory of meteors are solved numerically using the same ablation model developed by the authors for different fragmentation models. The influence of the heat transfer coefficient on the energy deposition of the bolide obtained using different fragment cloud models and the applicability of these models are studied.

The paper explores potential surface gravity waves in an ideal fluid described by Lambert W-functions. The shape of the undisturbed free surface is examined, depending on the magnitude of the wave. The characteristics of the deformed surface are derived. The influence of the wave amplitude on the dispersion characteristics, as well as on the group and phase velocities, is studied.

The short residence time of the fuel mixture in the operating chamber of the propulsion system at supersonic flow speeds significantly complicates its ignition. One of the promising areas associated with ensuring stable ignition of fuel mixtures in a wide range of speeds is the use of nonequilibrium plasma produced, for example, by a microwave discharge. Practical implementation of this direction requires a detailed analysis of plasma–chemical reactions occurring in the fuel mixture and finding the coefficients of the corresponding reactions. To find the coefficients of chemical reactions in a mixture of propane and air, the solution of the kinetic equation for the electron energy distribution function at a specified amplitude and frequency of the external electric field has been considered. Electrons are heated by a uniform electric field, collide with the components of the mixture, and perform elastic and inelastic collisions, which are taken into account as the dependence of the reaction cross section on the kinetic energy of the electrons. The obtained results processed as dependences of chemical reaction coefficients on the parameters of the external electric field are of interest for modeling the microwave discharge plasma used to ignite the fuel mixture.

It has previously been shown that the generalized Godunov–Kolgan scheme, unlike the Kolgan scheme, is able to exclude physically meaningless solutions in the numerical integration of the Euler equations for an inviscid gas and is easily adapted for calculation of single-component viscous gas flows. This paper proposes a modification to the generalized scheme for modeling viscous multicomponent gas flows based on the Navier–Stokes equations. To test the scheme, the problem of gas diffusion on a flat contact discontinuity is solved. We demonstrate the possibility of calculating diffusion flows and gas composition based on average, rather than minimum, concentration gradients within the computational cell. The proposed approach is more universal, easy to implement, and most importantly, it preserves the monotonicity of the solution and provides the second order of approximation in space on smooth solutions for all gas parameters, including component composition. A calculation with a frozen component composition within the calculation cell yields a first-order solution for the gas composition; however, for this problem its results are almost indistinguishable in terms of concentrations and similar for other gas parameters.