Shockwave processes in a shock tube equipped with a high-speed low-inertia electromagnetic pneumatic valve are experimentally investigated. Graphs of the pressure sensor signals in the shock tube channel are given. The dependence of the valve opening time on the pressure in the high and low gas density chambers is shown. A physical simulation of the valve operation at the initial moments of its opening with the formation of a shock wave is carried out.
Experiments on heat transfer in supersonic underexpanded jets of high-enthalpy nitrogen with ceramic samples based on HfB2–SiC are carried out at the induction RF plasmatron VGU-4 (Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences) at a pressure in the pressure chamber of 8.5 hPa, a gas flow rate through the discharge channel of 3.6 g/s, and an RF power of the plasma torch generator for anode supply of 64 kW. Three heat transfer modes are implemented using water-cooled conical nozzles with outlet diameters of 30, 40, and 50 mm. For the experimental conditions in supersonic modes, using a numerical method within the framework of the Navier–Stokes equations and simplified Maxwell equations, we simulate nitrogen plasma flows in a plasmatron discharge channel and the flow of dissociated nitrogen underexpanded jets around a cylindrical holder with a ceramic sample. From a comparison of the experimental and calculated data on heat fluxes to the surface of three samples, the effective coefficient of heterogeneous recombination of nitrogen atoms on the surface of ultra-high-temperature ceramics (UHTCs) at temperatures of 2273–2843 K is determined.
This paper presents the results of the numerical simulation of the initial stage of a pulsed inhomogeneous flow of a gas-dispersed mixture as a prototype of the jet powder technology of fire extinguishing or pollution neutralization. New physical effects of a pulsed inhomogeneous jet are revealed: the simultaneous existence of anomalous subsonic and supersonic shock-wave structures, as well as a resonant increase in the mass flow rate of the mixture compared to a homogeneous flow.
To investigate the effect of various notch damages at the blade tip of a pressurized rotor blade on the aerodynamic performance, the repair margin of blade tip notch damage and obtaining its spacing in the wing polish in size is explored. Based on the Rotor 37, a model of a blade with a notch depth between 0–0.3 mm and 0.3–5 mm is obtained, and the calculation model of the single-pass aerodynamic performance before and after the damage is constructed. Numerical simulations of the full 3D viscous flow field are carried out for the design and near-surge conditions, and the data are compared and analysed. The following results are obtained: the mass flow rate increases with the notch depth; the pressure boosting capacity slightly increases and then significantly decreases when the notch depth exceeds 1 mm; the stability margin is lower than 15% after the tip notch damage exceeds 0.23 mm and decreases with the notch depth; and the tip notch does not significantly affect the aerodynamic performance of the intact blade section at the height under the notch. When the notch depth exceeds 0.23 mm, the blade starts to show a near-stall trend, and when the notch depth approaches 5 mm, it demonstrates the near-stall operating condition.
Based on realistic traffic conditions, the macroscopic traffic flow model that considers the driver’s anticipation and traffic jerk effect is improved, and the bifurcation theory is used to describe and predict nonlinear traffic phenomena on the road from the perspective of global stability. Firstly, the linear stability conditions and the Korteweg–de Vries–Burgers equation are derived using linear and nonlinear methods to characterize the evolution of traffic flow. The type and stability of the equilibrium solution are discussed using the bifurcation analysis method, and the conditions of existence of the Hopf bifurcation and saddle-node bifurcation are proved. Numerical simulations show that the model can describe the complex nonlinear dynamic phenomena observed on the road. The bifurcation analysis will be helpful for improving our understanding of stop-and-go and sudden changes in stability in real traffic flow.
The study considers a two-dimensional flow of a viscous perfect gas around thermally insulated bodies. Using a composite Bézier curve to describe various body shapes and leveraging a reinforcement learning algorithm, we identify optimal shapes that minimise two distinct objective functions reflecting local or global surface temperature. We show that even at the Reynolds number ({text{Re}} = 200), Mach number M = 0.4, and Prandtl number ({text{Pr}} = 0.72), one can observe surface temperatures dropping below the free-stream value—a phenomenon known as aerodynamic cooling or the Eckert–Weise effect. The lowest local temperatures are attained at the rear of slender cross-flow plates, exhibiting a time-averaged recovery factor of –0.26, contrasting with 0.31 observed in the canonical flow around a circular cylinder. However, such shapes are not optimal in terms of the surface-averaged temperature of the body—boomerang-like shapes yield the lowest overall temperatures, with a global recovery factor of 0.34, in contrast to 0.63 for the circular cylinder. By independently varying the frontal and rear parts of the body, we propose a rationale behind these optimal shapes.
The phenomena of droplet impact on the heated liquid surface are difficult to unify due to complexity of the interaction, but this process has significance for the study such as direct fuel injection in internal-combustion engines or pool fire suppression. A series of experiments on a water droplet impacting on the heated glycerol surface are carried under various surface temperatures (111.4°C ≤ Tgly ≤ 270.6°C) and impact Weber number (50.5 ≤ We ≤ 297.9). Four regimes, including penetration, crater–jet, vapor explosion and crater–jet–vapor explosion, are discussed in detail. With increase in the Tgly and We, the phenomena transform easier from penetration to crater–jet. The jet formation is affected by the interaction of vapor explosion (Tgly ≥ 222.3°C) and this process is mainly caused by two factors: the vapor explosion appears at the liquid-liquid interface and the vapor explosion time is equal to 4.8–15.8 ms. Increase in Tgly and We prolongs the crater evolution process and leads to growth of the maximum dimensionless crater depth (hmax). The contribution index shows that hmax is significantly increased by the vapor explosion and continued to increase for the higher We. Furthermore, the secondary breakup of droplets is observed at Tgly ≥ 222.3°C and this phenomenon mainly includes the processes of puffing, sputtering, vaporization and deformation.
The paper numerically simulates the propagation of a shock wave through a gas suspension. The carrier medium is described as a viscous, compressible, heat-conducting gas. The mathematical model implements a continuum method for the dynamics of multiphase media, taking into account the interaction of the carrier medium and the dispersed phase. The mass transfer of disperse inclusions suspended in the gas, caused by the interaction of the shock wave with monodisperse gas suspensions and with gas suspensions having a multifractional composition, is modeled. Differences in the mass transfer of particles depending on the particle size are revealed. It is also found that the process of mass transfer of dispersed inclusions in a monodisperse gas suspension differs from a similar process for a fraction of a polydisperse gas suspension having the same particle size and the same volumetric content.
A model of a two-phase flow of compressible immiscible fluids is presented. Its derivation is based on the use of the theory of symmetric hyperbolic thermodynamically compatible systems. The model is an extension of the previously proposed thermodynamically compatible model of compressible two-phase flows due to the inclusion of new state variables of a medium associated with surface-tension forces. The governing equations of the model form a hyperbolic system of differential equations of the first order and satisfy the laws of thermodynamics (energy conservation and entropy increase). The properties of the model equations are studied, and it is shown that the Young–Laplace law of capillary pressure is fulfilled in the asymptotic approximation at the continuum level.
For a power-law elliptical body, the drag force in a high-speed rarefied gas flow is calculated based on several local models. By solving the variational problem, the exponent in the generatrix for a minimum drag body of various aspect ratio is determined depending on the ellipticity coefficient.
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