Fluid Dynamics最新文献

The problem of modeling the entry of a meteoroid into the atmosphere and its interaction with it is considered. The motion, ablation, and energy deposition of a meteoroid or its fragments moving as a single body are modeled within the framework of meteor physics equations. The main parameter of these equations is the ablation parameter, equal to the ratio of the heat transfer coefficient to the effective heat of mass loss. Due to the lack of data from theoretical and experimental studies on the determination of the effective heat of ablation at high meteor velocities, its constant value is usually used in the literature. In this paper, it is proposed to use the effective heat of ablation variable along the trajectory, interpolating its value between the heat of evaporation and the heat of melting (or spallation), depending on the flight velocity. By numerically solving the meteor physics equations, we study the influence of the way of setting the effective heat of ablation and its uncertainty on the simulated characteristics: the meteoroid velocity, as well as the change in its mass and energy deposition along the trajectory and on the trajectory itself; and the inaccuracy in determining these characteristics is evaluated.

The results of the numerical solution of the Boltzmann kinetic equation for intense evaporation from the interfacial surface are used to calculate the kinetics of the bulk condensation process near the evaporation surface. It is shown that during the period of existence of the supersaturated state, predicted based on the solution without taking condensation into account, the condensation aerosol has time to form. When analyzing evaporation from the interfacial surface, it is necessary to take into account the presence of formed droplets in the vapor phase and the thermal effect of condensation on vapor parameters.

The results of calculations of detonation flows in various gaseous mixtures containing H₂, O₂ are presented. A comparison with published theoretical and experimental results is carried out.

In this paper, the issues of the structural-parametric identification of kinetic models intended for the mathematical modeling of physical and chemical processes in gas dynamics are discussed. Two methods to estimate the temperature dependence of the rate constants of gas-phase chemical reactions are analyzed: the standard model based on the well-known Arrhenius formula and a new one proposed relatively recently. The focus of the article is on the basic parameter of the temperature dependence of the rate constants, i.e., the activation energy. The values of activation energy for combustion reactions of a mixture of hydrogen and oxygen that are obtained by approximation of the experimental data based on the Arrhenius formula, calculations based on the theory of the transition state, and values of activation energy obtained using a new model are compared. According to this model, the activation energy for exothermic reactions is always zero, while the activation energy for endothermic reactions is determined by the difference between the potential energies of the final and initial states in the given reaction and is numerically equal to its absolute value. The application of this method for estimating the activation energy is shown to produce results that are in good agreement with the empirical data.

In the paper, we present the results of an experimental study of a hydrophobic liquid flow between non-concentric cylinders. In the region of flow expansion, gas cavitation of the dissolved gas can be observed depending on the gap size between the cylinders. If the liquid contains water, steam cavitation of the impurity can be also observed. Steam cavitation of water occurs when the surfaces of the cylinders with a small gap slide between each other. Water vapor condenses into microdroplets when the flow stops. Three-phase gas bubbles with water microdroplets are formed at the gas-liquid interface. This gas bubble design is shown to have its own electric field. When a bubble rises, its water microdroplet moves along the gas-liquid interface and occupies a minimal distance from the surface of the neighboring bubble. In the case of several three-phase bubbles located nearby, the water microdroplets in them split, indicating the direction of the neighboring electric field sources. A patent for a method of registering sources of quasi-static electric fields was obtained based on the performed research.

This article presents the results of the heat flux measurement on a flat channel plate and a cylinder within a gas stream. The developed calorimetric sensors are used simultaneously with the coaxial thermocouple. The resulting measurement of heat flux show that calorimetric sensors can be used in test modes.

The process of volume annihilation of particles and antiparticles in the gravitational self-field is considered. The problem of homogeneous compression of such a system is solved both within the framework of the general relativity theory and in Newtonian mechanics. Two models of collapsing matter are considered, namely, hot and cold dust filled with radiation. The radiation pressure gradient is taken into account.

To address the scientific inquiry regarding the dynamic mechanism of deformation of droplets on the jet surface, this study establishes a stochastic differential equation describing deformation of a droplet on a uniform jet surface, considering the affine deformation of a semi-ellipsoidal droplet driven by the pulsation velocity of the jet. The results indicate that the equilibrium point set of the model conforms to an inverse proportional function concerning the major and minor axes of the droplet. Additionally, the assumption of the physical model is satisfied only when the droplet position parameter (theta in left( {left. {frac{{{pi }}}{2},{{pi }}} right]} right.). The solution process, initialized with the equilibrium point set, tends to reach the state of mean square instability within a very short duration. For dimensionless initial semi-minor axes of the droplet below 0.1 and within the constraint of the equilibrium point set, the probability of the droplet being in a stretched state during the later stages of deformation ranges between 60 and 65%. In this model, during the late stage of droplet deformation, the dimensionless semi-minor axis of the droplet approaches zero. Thus, when the droplet is in the stretched state, it is close to breaking. During retraction, the length of semi-major axis of the droplet fluctuates and gradually decreases. However, in the stretched state, the length of semi-major axis of the droplet increases rapidly, with its growth rate accelerating with time.

The impact of molten aluminum droplets on a solid surface at a temperature of 1173 K is numerically simulated using the volume of fluid model. The spreading patterns of droplets with various initial velocities and diameters on surfaces with various wettability are investigated, and the velocity distribution, the spreading factor, the height factor, the spreading time, and other parameters of the molten droplets in the impact process are analyzed. The simulation results show that the larger the contact angle, the smaller the wetting radius; the smaller the static contact angle, the smaller the surface and the stronger the droplet adhesion. As the initial velocity of droplet increases, the maximum spreading factor also increases and a jet is generated at the center of droplet. However, change in the initial velocity has a negligible effect on reaching the maximum spreading state. The amplitude and frequency of droplet oscillations increase significantly with the droplet diameter, the smaller droplets deforming faster and stabilizing more easily. Moreover, α is the revised factor in Pasandideh–Fard model based on the energy conservation law. This study aims to provide a theoretical basis for the wetting and spreading adhesion of aluminum liquids in production of electrolytic aluminum.

In experiments on a dual-mode scramjet combustor utilizing kerosene fuel, closed-loop control tests are conducted using the resistance-heated pure air supersonic combustion test equipment with the wall pressure or the pressure ratio as controlled parameters. The results revealed faster response to changes in the kerosene flow rate when controlling the wall pressure downstream of the injection point as compared to the near injection point. The closed-loop control scheme achieved objectives with the error smaller than 2% for various parameters, demonstrating the repeatability and the broad applicability. During the hydrogen-single combustion phase, the combustor operated in the supersonic combustion mode, while during the mixed combustion phase of hydrogen and kerosene, the combustor operated in the subsonic combustion mode. The backpressure caused by combustion affects the isolator inlet, and during the kerosene-single combustion phase, the combustor operates in the subsonic combustion mode.