Fluid Dynamics最新文献

The design and analysis of a scramjet inlet and isolator system for hypersonic flight are presented. Both theoretical methods and computational fluid dynamics simulations are employed to study oblique shock compression, pressure recovery and variations in the temperature at the Mach numbers 6–10 for altitudes of 0–20 km. A grid independence study is performed using the standard k–ω turbulence model for ensuring the solution accuracy. The results show significant pressure rise and Mach number reduction at the isolator exit, with the total pressure recovery reaching up to 82% at the Mach number equal to 10 for the ground conditions. The static temperature levels at the isolator exit ranges from 1210 K (20 km, the Mach number 6) to 2740 K (sea level, the Mach number 10), posing material challenges for inlet design. The findings validate the feasibility of the proposed inlet geometry and provide critical insights into thermal management and structural design of hypersonic scramjet systems.

The design, development, and validation of a physiological pulsatile cardiovascular flow simulator to analyse the hemodynamic behaviour in stenosed blood vessels is studied. The simulator consists of an innovative arrangement of peristaltic pumps to reproduce realistic arterial pulse waveforms, incorporating the higher harmonic components of physiological flow. Experimental investigations were performed using a laser Doppler velocimetry (LDV) system to evaluate the axial velocity, the wall shear stress (WSS), the turbulence intensity, and related flow parameters in vessels with varying stenosis severities (12.5, 25, and 50%). The observed results indicated that stenosis severity critically influences the flow structure, with higher blockages inducing significant velocity skewness, increased oscillatory WSS, and sustained post-stenotic disturbances. Flow reversal, vortex formation, and prolonged laminar recovery were observed downstream of severe stenoses. Comparative analyses with theoretical models validated the experimental accuracy, particularly in central and mid-radial zones. The study also introduced a method for determining the oscillatory shear index (OSI) and the relative residence time (RRT), identifying regions susceptible to atherogenesis. The simulator provides a reliable platform for replicating in vivo-like flow patterns in vitro, providing the valuable insights into the disease progression mechanisms and enabling future development of diagnostic and interventional strategies in cardiovascular medicine.

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.