Fluid Dynamics最新文献

The article presents an overview of the studies carried out in the Institute of Mechanics of Moscow State University in 2021–2024. The results of experimental studies of the application of wave propulsors (WP) of the flapping wing type and direct-flow wave propulsors (DFWP) on a 1700 mm-long model of a small waterline area vessel (SWAV) are presented. The NACA0015 profile is used as a working element of both the flapping and direct-flow WPs. In the case of the direct-flow WP the profile is rigidly fixed against the hull with the wing chord inclination of 30°. The efficiency of using the WPs of the underwater sail type is also studied. Different WP types are tested on a smaller-scale DFWP model, 840 mm in length. Comprehensive studies of the efficiency of the direct-flow WPs and the underwater sail type WPs are carried out on a small model. An inclined plate is used as a working element of the direct-flow WP. The optimal parameters of the direct-flow WP (length, inclination, plate immersion) are experimentally determined. The effect of the hull immersion depth (draft) and the immersion depth of the underwater sail type WP on the vessel velocity counter waves is studied. The experiments show that the efficiency of flapping wings or underwater sail wave propulsors in the operating range of wave frequencies is slightly higher than that of DFWP. However, in stormy sailing conditions, DFWP has an advantage, since it shows the highest efficiency just in such conditions, while the other options considered are effective in the operating range of wavelengths that depends on the ship length and, generally speaking, does not coincide with the length of storm waves.

The most significant results of numerical study of the processes in heat exchangers with diffuser channels, obtained by the authors between 2020 and 2024, are reviewed. The plate and double-pipe heat exchangers with various gaseous and liquid coolants are considered. The performed studies showed that the amount of heat transferred from the “hot” to “cold” coolant increases as compared to heat exchangers with smooth channels of constant cross-section, due to the enhancement of heat transfer in heat exchangers with diffuser channels. The results obtained can serve as a basis for the development of new advanced heat exchangers.

Numerical simulations of turbulent separated air flow and heat transfer over a thermally insulated plate containing single V-shaped grooves with hemispherical ends and opening angles of 95°, 180°, and 275° on an isothermal rectangular insert were performed by solving the Reynolds-averaged Navier–Stokes and energy equations using multiblock computational techniques. The closure of the momentum equations employed the differential equations of the SST shear stress transport model. The results revealed a fundamental difference in the mechanisms that enhance separated flow and heat transfer in the grooves, associated with the formation of a U-shaped vortex at the bend of the V-groove and two tornado-like vortices at the upstream-facing ends of the Λ-shaped groove. A localized static pressure drop of about 0.3 between the external flow stagnation regions and low-pressure zones accelerated both the recirculating and secondary swirling flows. The total relative heat transfer from the rectangular section bounding the contour of the V-groove increased by nearly 30% compared to a flat plate, whereas for a transverse groove, the corresponding value reached 1.12.

The air-cushion craft that had appear in the thirties of the last century have been thus far among the best two-medium vehicles. However, the caterpillar tracked surface craft developed in recent years (snow mobiles) are in certain cases not inferior to them as concerns their running and operation performance. They are capable to roll over the water surface at a large velocity, their advantages being obvious in the case of motion over dry and shallow water. We note also that that the caterpillar tracks play the role of loth load-bearing surfaces and propulsors, which offers also certain advantages. In this paper, we discuss the hydrodynamic forces acting on caterpillar tracks in the case of the rolling over a free water surface and present certain experimental data.

The results of studies conducted at the EKUD experimental complex of the Institute of Mechanics of Moscow State University over the past ten years are analyzed. They include primarily the radiation characteristics of shock-heated gases measured in a wide range of wavelengths (λ = 115–1100 nm) at shock wave velocities up to 11.4 km/s and the gas pressure in front of the shock wave of 0.25 Torr, as well as the ignition characteristics of combustible mixtures based on hydrogen, propane, and propylene obtained at both low (T ≤ 1000 K) and high (T ≥ 1000 K) temperatures. Electron concentrations in the low-temperature plasma in the vicinity of a strong shock wave were measured.

Topical questions of constructing a model for measuring the rate constants of gas-phase chemical reactions are considered. These questions include aligning the experimental conditions and the initial data for a system of kinetic equations, constructing analytical models of kinetic curves, and estimating the rate constants for the reaction considered and the secondary processes. Using the example of one of the important chemical reactions, OH + O → O₂ + H, which is a part of the mechanism of combustion of a hydrogen-oxygen mixture, the problem of selecting the optimum method for processing the experimental kinetic curves is solved. The optimization criterion is obtaining a more complete volume of information on the rate constants of both primary and secondary processes, as well as the fulfillment of requirements for the convergence of the results of the iterative process for determining the rate constants for different experimental conditions for obtaining the kinetic curves and identical conditions that determine the measured quantity. The principle of “invariance of the measured quantity” is used to estimate the rate constants of secondary processes. This principle states that, under the experiment conditions that the measured quantity is constant, the method for determining the quantity should ensure a minimum range of variation in its values. In constructing the model and its optimization, for four processes in the base set (58 reactions), the changes in the rate constants were recorded at the temperature T = 298 K under the experimental conditions in which molecular hydrogen serves as the source of hydroxyl OH.

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.