Thermophysics and Aeromechanics最新文献

We propose to improve a new experimental methodology of determining the amplitude-frequency characteristics of a system of hot-wire anemometry with the use of a short-pulse laser action on the hot-wire sensor. Mistakes of the previous study are taken into account. The amplitude-frequency characteristics of a constant-temperature anemometer (CTA) with a wire sensor are obtained, and comparisons with the results obtained by a standard method of determining the amplitude-frequency characteristics are performed.

The Direct Simulation Monte Carlo (DSMC) method is widely used to solve problems of rarefied gas dynamics. The choice of the model of particle collisions with each other in implementation of the DSMC algorithm significantly affects the accuracy of simulations and the complexity of computations. One of the most popular particle collision models is the Variable Soft Sphere (VSS) model. In the present study, we simulate a flow arising when a heated wire is placed into a quiescent gas atmosphere (helium or argon). It is shown that the use of the VSS model with parameters based on viscosity and diffusion can lead to errors in estimating the heat flux from the wire to the ambient gas.

This study examines the entropy production occurring within the flow of an incompressible Jeffrey fluid through a sloping channel, incorporating the influences of hall current, Soret parameter, thermal radiation, and angled magnetic field. The derived governing equations are renovated into dimensionless governing equations through the utilization of similarity variables. The technique of spectral quasi-linearization method (SQLM) is applied to ascertain the solution. Graphs are employed to investigate and illustrate the impact of novel thermophysical parameters. With the use of tabular data, variations in skin friction, the Nusselt number, and the Sherwood number are also discussed. The findings indicate that increasing the Soret parameter, inclination angle, hall current, radiation parameter, and Jeffrey fluid parameter increases entropy generation. Conversely, entropy generation decreases with higher values of the inclination angle of the channel.

An impinging jet with passive control of mixing and heat transfer with the use of a grid at the inlet is numerically studied. It is shown that the local Nusselt number at the stagnation point on the heated surface with which the jet is impinged, and the Nusselt number averaged over the area with intense heat transfer, increase with increasing Reynolds number in accordance with a power law corresponding to the empirical approximation. It is found that addition of a grid, especially fractal grid, leads to noticeable enhancement of heat transfer in the central part of the jet. The results of the previous measurements are compared with effects predicted by the present computations, and the prospects of further investigations are determined.

The accurate study of heat transfer between water and steam at high pressures was achieved on a developed and tested model of a mixing unit for heat transfer flows (Direct-Contact Water Heater — DCWH). The test results showed that the water underheating to the saturation temperature at the model outlet is less than 1 and 2°C for two- and single-tray arrangement of the water-separation unit in the model, respectively. The droplet flow model is preferable for thermal calculation of the heating block in the DCWH.

Physics-Informed Neural Networks (PINNs) represent an innovative method for solving a wide range of problems in mathematics, physics, and engineering. PINNs combine the neural networks concepts and physical equations aimed at modeling and analyzing various physical processes. In particular, PINNs can be applied to solve differential equations, including the one-dimensional convection equation. The research shows that the standard implementation of PINNs efficiently solves a one-dimensional convection equation at relatively small convection velocity values, but diverges for higher values of this parameter. This paper provides an overview of existing approaches for solving the one-dimensional convection equation using PINNs and demonstrates improvement for model performance through different methods. The results of comparison indicate the superiority of the approach based on dynamically adjusting collocation points according to the residual at the current training step.

The paper presents the results of a study on the effect of catalytic hydrogen oxidation on heat transfer in an impinging jet under chemical activity on the sample surface. It is shown that with an increase in the percentage of hydrogen in the mixture with air, not only an increase in the heat transfer intensity is observed, but also the reaction zone expansion. Additionally, it is also noted that in the case of a chemically active jet, temperature pulsations (approximately 6 %), associated with the reactions of hydrogen catalytic oxidation, occur on the surface. At that, the form of generalized distribution of the temperature function along the surface radius remains almost the same for all cases involving heterogeneous chemical reactions. The exception is the case with 2 % molar hydrogen content in the jet, if there are regions with heat release from reactions lower than the convective heat transfer at a non-reacting flow.

The thermal diffusivity (a) of solid magnesium–lithium alloys with lithium contents X_Li = 5, 10, 17, 21, and 25 at. % was measured using a laser flash method in the temperature range of 300–680 K. Based on the experimental results, the thermal conductivity (λ) of alloys was calculated and compared with the literature values for λ of other compositions. The estimated uncertainties of the obtained data were 3.0–3.4 % for λ and 2.0–2.4 % for a. It is shown that the addition of lithium to magnesium reduces significantly its thermal conductivity, with a more pronounced decrease in λ observed as the Li concentration approaches X_Li = 32 at. %. Anomalous features in the form of bends in the temperature dependences λ(T) and a(T) were identified for the Mg₉₅Li₅ and Mg₇₅Li₂₅ alloys within the temperature range of 310–330 K, similar to the behavior reported for the Mg₇₀Li₃₀ alloy. Using the calculated data and literature sources, the concentration dependences of thermal conductivity for the Mg–Li system were plotted over the composition range X_Li = 0–32 at. %.

Development of concepts for multi-entry space vehicles put strict requirements for reliability of operating power plants and the flight vehicle as a whole. An important problem is achieving trouble-free performance of vehicle power plant operating under high thermal loads. This type of power plants consumes the hydrocarbon fuel with a high resistance to surface deposition of incomplete oxidation products.

The progress in production technologies for synthetic fuel from bio resource enables accessibility with reduced or zero carbon footprint. Synthetic fuel or its components are different from a hydrocarbon fuel by their composition, as well as by the fuel properties. The use of fuels with synthetic components requires a study on physical-chemical properties and thermophysical characteristics.

This paper presents experimental study on thermal stability, limiting cooling capacity and ignition parameters for a high-density hydrocarbon fuel (HDHF) from new-generation products. It was shown that the HDHF can be used at temperatures up to 300 °C without any deposits of with admissible low levels. Experiments were conducted in a shock tube for the fuel ignition delay in the operating range of pressure 14–16 bar, temperature 1000–1500 K and oxidizer excess ratio 0.5–3.

The paper presents the numerical simulation results for a near-wall film cooling with gas ejection through a nozzle shaped as a cavity with triangular cross section (with a backward facing step). The backward facing step induces the main flow detachment and generates coherent vortex structures with a constant vortex-shedding frequency (in the zone of mixing with the coolant jet). These vortex structures interact with the wall and improve the coolant spreading in the horizontal direction. This also improves the jet flow attachment to the surface at high blowing ratios. The cavity’s triangular shape reduces the generation of streamwise vortices that separate the near-wall flow from the surface. The study was conducted for a wide range of coolant blowing ratios. The wall boundary conditions were adiabatic. We determined the injection parameters range suitable for practical applications of the proposed nozzle design. The proposed flow model has a specific vortex shedding frequency and is sensitive to the external forcing at this frequency. Thus, the model is a prototype of an active control system for film cooling.