Fluid Dynamics最新文献

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.

Ground vehicle studies usually aim to reduce fuel consumption by applying special airflow control methods or modifications. The main aim of this project is to improve airflow around, especially the rear region of the body, and apply optimization to drag reduction. This work is relatively unique since the vortex generator (VG) is used as a passive control device by mounting on the slant surface of the body and the rear underbody diffuser is applied with rounded rear edges of the body and optimization is applied by using the genetic algorithm (GA) for all parameters of control devices. The aero-acoustic analysis is also performed using broadband noise source model and acoustic improvement is indicated by comparing baseline and optimized bodies. Few studies investigate all these analyses together in the literature. In this study, an analysis is performed using Computational Fluid Dynamics (CFD) simulation in the Fluent software, and validation is achieved by comparing experimental data reported in the literature. After mounting VGs and making modifications, the CFD solution is repeated using the k–k_L–ω transition turbulence model at 1.39 × 10⁶ and 2.78 × 10⁶ Reynolds numbers. The optimization process is carried out using nine design parameters of the vortex generator and the diffuser. The Central Composite Design (CCD) is used and 147 design points are obtained for the Design of Experiment (DoE). The genetic algorithm is then applied to find optimum design variables for minimizing the drag under specified constraints and airflow conditions. Finally, the results of the investigation of the modified and optimized body revealed that a significant reduction in the drag is achieved at about 13.28 and 19.16% for 1.39 × 10⁶ and 2.78 × 10⁶ Reynolds numbers, respectively, when compared with the baseline body. The results show that the size of the vortex is reduced and its formation on the slant surface is eliminated. In addition, it can be stated that aerodynamic noise is significantly reduced when observing the acoustic power level contours for baseline and optimized bodies.

In this paper, a theoretical study of kinetic processes occurring in argon–helium plasma of a pulsed discharge is presented. A model of argon–helium plasma is developed and key mechanisms of the formation and loss of plasma particles are studied. A general scheme of kinetic processes occurring in plasma of inert gases of a pulsed discharge is formed.

This paper provides a brief overview and clarification of the main results obtained over the past ten years at the P-2000 facility. The current data on the development of electric discharge stands of this installation are provided. The possibilities of using these stands for various applications are considered.

In this paper, the results, mainly experimental, on the energy separation in single-phase gas flows are reviewed. Special attention is paid to the field of scientific research of the authors: the effect of energy separation in the compressible gas boundary layer and the development of the methods and devices for machine-free temperature separation of a gas flow. The experimental data obtained by the author’s group are described in detail. Among the methods of energy separation, the Leontiev tube and exploring ways to increase its efficiency, energy separation in a channel with porous permeable walls, and the Eckert–Weise effect (aerodynamic cooling) in the transverse flow of a compressible gas stream around a single and pair of side by side cylinders are considered.

Capillary, gravity, and capillary-gravity surface periodic flows in different fluid models are investigated analytically using the theory of singular perturbations. Models of viscous and ideal, homogeneous, or uniformly stratified fluids are considered. The periodic surface flow in the viscous fluid model contains ligaments that are thin trickles, in addition to the wave component. Approximate expressions of the dispersion relations for all flow components in the models under consideration are presented. The studied components observed experimentally at all stages of the evolution of the drop impact flow.

The peculiarities of solving evaporation problems are analyzed. Different methods of setting boundary conditions for continuum mechanics equations are studied. This paper presents results of applying continuum mechanics equations together with the kinetic Boltzmann equation, as well as using molecular dynamic simulation, to find the velocity distribution function of molecules near the interface. The distribution function of molecules moving away from the interface is determined. It is shown that the evaporation and condensation coefficients in the considered problems are close to unity.

Using the method of high-speed video recording of the merging (coalescence) process of compound drops into deep water, the distribution patterns of the drop’s material over the target fluid’s deformed surface in the splash formation mode are traced during the recording of the fine structure evolution of the flow at the initial stage of the coalescence of compound drops. In the experiments, the droplets’ fall height, droplets’ diameter, and the compound ink-oil drop’s core position relative to its geometric center are varied. Fine structures are observed at all flow stages, starting from the contact of the droplet’s oil shell with the target fluid’s surface, followed by cavity formation, core spreading, and splash formation. Using direct measurements and spectral analysis, the characteristic dimensions of fine flows and structures are estimated.

The results of numerical study of the flow in a channel with an annular radial jet injected along the Coanda surface are given. To describe the flow of the gas medium, the two-dimensional axisymmetric Reynolds-averaged Navier-Stokes (RANS) equations are used in combination with equations of the semi-empirical k–ω SST turbulence model. The effect of the total pressure and the width of radial jet on the velocity and static pressure distributions is studied and changes in the local structure developed at the sub- and supercritical pressure in the jet are described.

To mitigate the adverse effects of aerodynamic heating on hypersonic vehicles, a tangential supersonic cooling film is typically used. This study investigates the impacts of the cooling film’s Mach number (Mj) on the flow field structure. Two supersonic cooling film configurations, with the Mach numbers of 2.0 and 2.3, were designed and tested in a supersonic wind tunnel at the freestream Mach number M = 3.8. The flow field structure was obtained using nanotracer-based planar laser scattering (NPLS), and the wall pressure were derived using an experimentally validated numerical simulation method. The results demonstrate that in the mixing layer at Mj = 2.0 instability between the freestream and the supersonic cooling film develops earlier than that at Mj = 2.3, occurring under an identical ratio of the static pressure (RSP) conditions. On convex surfaces, as the radius of curvature decreases, the influence of the cooling film’s M on ΔP/P_in diminishes; conversely, on concave surfaces, as the radius of curvature decreases, the influence of the cooling film’s M on ΔP/P_in increases. Beyond x = 240 mm, the development over curved surfaces becomes pronounced, and the static pressure of the supersonic cooling film has minimum impact on the wall pressure. Variation in the wall pressure is affected by both the coverage length and the curvature of the supersonic cooling film, and for the cooling film the higher Mj achieves a longer coverage length.