Fluid Dynamics最新文献

The main results of investigations carried out at the Institute of Mechanics of the Moscow State University over the past 10 years in the field of studying supersonic flow past annular cavities on conically pointed cylindrical bodies, including at angles of attack, are reviewed. The possibilities of some active and passive methods for controlling the regimes of flow past the cavity are also presented.

In the current study, we examine the linear instability in Poiseuille flow of an incompressible viscous fluid confined between two parallel inclined planes. We study the impact of the temperature gradient and the superimposed Couette flow on the onset of shear instability in Poiseuille flow in the form of Tollmien–Schlichting (TS) waves. The role of the inclination of the fluid layer and the Prandtl number of the fluid on the onset of TS instability is observed to be significant in the presence of the temperature gradient, indicating the complex interplay between the thermal effects, the fluid properties, and the geometric factors.

The plane problem of the motion of a wave front over the surface of an ideal incompressible fluid of finite depth at a constant velocity is considered. The initial solution in the form of a smooth bore tends to a steady-state flow. A time-dependent solution in the form of a second-order nonlinear equation is obtained. The stationary form of the equation is compared with well-known results by Lavrent’ev and Korteweg-de Vries (KdV). The linearization agrees with the Airy theory with high accuracy. The accuracy of the solution is estimated numerically. The result, in the form of a nonstationary wave bore, agrees with observations.

A brief review of studies devoted to the destruction of phenolic materials is carried out. Several kinetic models of phenol decomposition are considered. Calculations of phenol decomposition according to the front model are performed for a number of initial data.

The behavior of chlorobenzene and aniline droplets as they fall into water is investigated combining experimental observations with numerical simulations. In the experimental stage, key parameters such as the time-dependent velocity u(t), the terminal velocity U_T, and the equivalent diameter d_eq of each droplet were accurately measured. For the numerical approach, computational fluid dynamics (CFD) methods were applied, employing the finite volume technique to solve the Navier–Stokes equations, along with the volume of fluid (VOF) model to capture the liquid–liquid interface. The experimental velocity–time data served as a basis for validating the simulations through curve fitting and regression analysis, revealing a strong correlation between the experimental and numerical outcomes. Additionally, the study explored the coalescence dynamics of two identical droplets positioned side by side in water. Results showed that a smaller initial distance between the droplets notably hastens the coalescence process, especially during direct, head on collisions.

Flow of a rarefied gas mixture (neon-argon) in a cylindrical channel under the action of a pressure gradient and in the presence of wall rotation in the direction opposite to the gas flow is investigated. The problem is studied numerically using the direct simulation Monte Carlo (DSMC), method. It is shown that the combination of the pressure gradient and wall rotation leads to the effect of separation of the gas mixture during flow in the rarefied regime. The dependence of the separation effect on the wall rotation speed, the degree of rarefaction of the gas, and the channel length is studied.

The dynamics of a nonequilibrium acoustically active gas are considered. In such a gas, sound waves become unstable due to relaxation processes, and, at the nonlinear stage of evolution, form a quasi-stationary system of shock-wave pulses propagating at a supersonic velocity from the disturbance source. Based on the numerical gas-dynamic simulation methods, it is shown that the dynamics and structure of these shock-wave pulses depend on the model of the vibrational relaxation time. If this relaxation time decreases with increase in the temperature more rapidly than a certain critical value, then conditions for the development of local thermal instability between the shock wave fronts can arise. In the domains with a high degree of nonequilibrium of the medium, the instability leads to a thermal explosion and the formation of strong shock waves with a small density jump. These shock waves do not have the property of evolutionarity, and therefore, they relax with time to a stable state corresponding to the structure of shock-wave pulses. A detailed analysis of the numerical simulation results shows that the intensity and the structure of shock-wave pulses are independent of initial disturbances, but determined only by the initial parameters of the nonequilibrium medium. Consequently, the system of shock-wave pulses is a nonlinear autowave structure. The convergence of the numerical solutions to the exact solution is investigated when the flow structure of nonequilibrium vibrationally excited gas is described in the neighborhood of the shock wave front. It is shown that there is a good agreement between the structure of shock waves obtained in the numerical models and the nonequilibrium shock adiabatic curve written in the Rankine–Hugoniot form with an additional term that takes into account the vibrational-translational energy exchange in the shocked gas over the width of the numerical front.

The drop impact, a fundamental topic in fluid mechanics, plays a pivotal role in diverse engineering applications such as atomization, evaporation, spray coating, and surface cooling. This study systematically examines the key factors governing droplet impact phenomena, employing dimensionless analysis to establish universal scaling relationships for characterizing the process. Classical theoretical frameworks are reviewed to outline the governing mechanisms of post-impact behaviors, including spreading, splashing, and receding, while highlighting their distinct morphological evolution under varying conditions. Furthermore, recent experimental advancements are critically evaluated to address emerging challenges, such as the influence of surface topography, fluid rheology, and environmental parameters on impact outcomes. By integrating foundational theories with contemporary research, this review provides a structured synthesis of the field, aiming to bridge theoretical insights with practical engineering needs. The work serves as a reference guide to foster innovation in applications reliant on precise control of droplet-surface interactions.

The impact of a star-shaped ring tab on the dispersion and mixing characteristics of a subsonic jet is studied. The unique tab geometry, with multiple apex edges, generates counter-rotating vortices of varying scales that interact with the shear layer. Experiments were performed at the nozzle jet exit Mach numbers of 0.4, 0.6, and 0.8, and the outcomes were compared with those of an uncontrolled free jet. The introduction of the star ring tab results in a notable reduction in the potential core length, approximately 30, 50, and 87.5% at the Mach numbers of 0.4, 0.6, and 0.8, respectively, accompanied by enhanced jet decay rates relative to the baseline configuration. The radial Mach number profiles and the contour plots highlight the increased jet spread and deflection from the geometric centerline. Thrust vectoring was achieved with deflection angles of 1.4° at the Mach number 0.4, and 2.9° at the Mach number 0.8. The findings demonstrate the potential of star ring tabs to improve the mixing efficiency, support the thrust vectoring, and contribute to noise reduction in subsonic jet applications.