Fluid Dynamics最新文献

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.

The effect of varying disk diameters on drag reduction and the flow field for a hemispherical blunt body equipped with a hemispherical disk spike and moving at a hypersonic velocity is investigated. Axisymmetric simulations are performed to evaluate the effects of various disk diameters on the characteristics of flow around the body. The results indicate that increase in the disk diameter up to an optimal diameter of 18 mm leads to a reduction in both the drag force and the heat load. For the greater disk diameters, the drag force increases instead of decrease, demonstrating that the larger disk diameters become ineffective in further improving the aerodynamic performance. A density contour analysis reveals that, as the disk diameter increases, the strength of the reattachment shock weakens; however, beyond a certain threshold, the shock strength increases, correlating with the rise in drag. These findings suggest that there exists an optimal disk diameter for minimizing the drag and the heat load, while the larger diameters lead to negative aerodynamic effects.

To achieve rapid calculation of the aerodynamic forces of multi-wing butterfly-inspired ornithopters during flight, a quasi-steady aerodynamic force calculation method driven by multiple parameters and based on the blade element theory (BET) is proposed. This quasi-steady method can describe the flapping motion, the wing shape and the deformation rules of each wing, whether observed or expected, and calculate the instantaneous aerodynamic forces of the ornithopter according to the incoming flow conditions. The motion phase differences of each wing in the multi-wing ornithopter are also taken into account. Compared with the aerodynamic force measurement experiment of a 200-mm wingspan butterfly-inspired ornithopter, and considering the influence of the wing moment of inertia on the experimental measurement, the results show that the instantaneous values of the lift and thrust forces are consistent, and the maximum normalized peak error of the instantaneous lift force is 7.2%, and that of the instantaneous thrust force is 5.7%. This method can effectively describe changes in the aerodynamic force during the flight of butterfly-inspired ornithopters and provide guidance in the preliminary design stage.